Network Working Group M. Nystr÷m
Internet-Draft RSA Security
Expires: August 18, 2005 February 14, 2005
The Protected One-Time Password Protocol (EAP-POTP)
draft-nystrom-eap-potp-00
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document describes a general EAP method suitable for use with
One-Time Password (OTP) tokens, in particular tokens with direct
electronic interfaces to their associated clients. The method can be
used to provide unilateral or mutual authentication, and key
material, in protocols utilizing EAP, such as PPP, IEEE 802.1X and
IKEv2.
Nystr÷m Expires August 18, 2005 [Page 1]
Internet-Draft EAP-POTP February 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Background . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Rationale behind the design . . . . . . . . . . . . . . . 4 2. Conventions used in this document . . . . . . . . . . . . . 6 3. Authentication model . . . . . . . . . . . . . . . . . . . . 7 4. Description of the EAP-POTP method . . . . . . . . . . . . . 8 4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2 Version negotiation . . . . . . . . . . . . . . . . . . . 10 4.3 Session resumption . . . . . . . . . . . . . . . . . . . . 11 4.4 Key derivation . . . . . . . . . . . . . . . . . . . . . . 12 4.5 Error handling . . . . . . . . . . . . . . . . . . . . . . 13 4.6 Slowing down attackers . . . . . . . . . . . . . . . . . . 13 4.7 EAP-POTP packet format . . . . . . . . . . . . . . . . . . 14 4.8 EAP-POTP TLV objects . . . . . . . . . . . . . . . . . . . 17 4.8.1 Version TLV . . . . . . . . . . . . . . . . . . . . . 17 4.8.2 Server-Info TLV . . . . . . . . . . . . . . . . . . . 18 4.8.3 OTP TLV . . . . . . . . . . . . . . . . . . . . . . . 20 4.8.4 NAK TLV . . . . . . . . . . . . . . . . . . . . . . . 28 4.8.5 New PIN TLV . . . . . . . . . . . . . . . . . . . . . 30 4.8.6 Confirm TLV . . . . . . . . . . . . . . . . . . . . . 32 4.8.7 Vendor-Specific TLV . . . . . . . . . . . . . . . . . 35 4.8.8 Resume TLV . . . . . . . . . . . . . . . . . . . . . . 37 4.8.9 User Identifier TLV . . . . . . . . . . . . . . . . . 38 4.8.10 Token Serial Number TLV . . . . . . . . . . . . . . 39 4.8.11 Time Stamp TLV . . . . . . . . . . . . . . . . . . . 40 4.8.12 Counter TLV . . . . . . . . . . . . . . . . . . . . 41 5. Profile of EAP-POTP for RSA SecurID . . . . . . . . . . . . 43 6. Security considerations . . . . . . . . . . . . . . . . . . 44 6.1 Security claims . . . . . . . . . . . . . . . . . . . . . 44 6.2 Passive and active attacks . . . . . . . . . . . . . . . . 44 6.3 Denial of service attacks . . . . . . . . . . . . . . . . 46 6.4 The use of pepper . . . . . . . . . . . . . . . . . . . . 46 6.5 The race attack . . . . . . . . . . . . . . . . . . . . . 46 7. IANA considerations . . . . . . . . . . . . . . . . . . . . 48 8. Intellectual property considerations . . . . . . . . . . . . 49 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 50 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 51 10.1 Normative references . . . . . . . . . . . . . . . . . . 51 10.2 Informative references . . . . . . . . . . . . . . . . . 51 Author's Address . . . . . . . . . . . . . . . . . . . . . . 52 A. Examples of EAP-POTP exchanges . . . . . . . . . . . . . . . 53 A.1 Basic mode, unilateral authentication . . . . . . . . . . 53 A.2 Mutual authentication without session resumption . . . . . 53 A.3 Mutual authentication with transfer of pepper . . . . . . 55 A.4 Failed mutual authentication . . . . . . . . . . . . . . . 56 Nystr÷m Expires August 18, 2005 [Page 2]
Internet-Draft EAP-POTP February 2005 A.5 Session resumption . . . . . . . . . . . . . . . . . . . . 58 A.6 Failed session resumption . . . . . . . . . . . . . . . . 59 A.7 Mutual authentication, and new PIN requested. . . . . . . 61 A.8 Use of next tokencode mode . . . . . . . . . . . . . . . . 63 B. Use of the MPPE-Send/Receive-Key RADIUS attributes . . . . . 65 B.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 65 B.2 MPPE key attribute population . . . . . . . . . . . . . . 65 Intellectual Property and Copyright Statements . . . . . . . 66 Nystr÷m Expires August 18, 2005 [Page 3]
Internet-Draft EAP-POTP February 2005 1. Introduction 1.1 Scope This document describes an EAP method suitable for use with One-Time Password (OTP) tokens, in particular tokens electronically connected to a user's computer, e.g. through a USB interface. The method can be used to provide unilateral or mutual authentication, and key material, in protocols utilizing EAP, such as PPP [9], IEEE 802.1X [10] and IKEv2 [11]. 1.2 Background A One-Time Password (OTP) token may be a handheld hardware device, a hardware device connected to a personal computer through an electronic interface such as USB, or a software module resident on a personal computer, which generates one-time passwords that may be used to authenticate a user towards some service. Increasingly, these tokens work in a connected fashion, enabling programmatic retrieval of their OTP values. This document describes an EAP method intended to meet the needs of organizations wishing to use these connected OTP tokens in an interoperable and programmatic manner to authenticate users over EAP. The method is designed to be independent of particular OTP algorithms. The basic variant of this method provides client authentication only. A more advanced variant provides mutual authentication, integrity protection of the exchange, protection against eavesdroppers, and establishment of authenticated keying material. The advanced variant also allows for fast session resumption. While this document also includes a profile of the general method for the RSA SecurID(R) mechanism, it is described in terms of general constructions. It is therefore intended that the document will serve as a framework for use also by other OTP algorithms. Note 1: The RSA SecurID product is a hardware token card (or software emulation thereof) produced by RSA Security Inc., which is used for end-user authentication. Note 2: The term "OTP" as used herein shall not be confused with the EAP OTP method defined in [1]. 1.3 Rationale behind the design One advantage of defining a new, general, EAP method for OTP token technology is that the protocol syntax becomes well defined. This makes it easier to programmatically use the EAP method in the peer Nystr÷m Expires August 18, 2005 [Page 4]
Internet-Draft EAP-POTP February 2005 and the authenticator. This is unlike, e.g., the Generic Token Card (GTC) method, which uses text strings, intended to be interpreted and acted upon by humans. The advantage of using a GTC profile for a particular OTP technology would be that of reduced deployment costs, assuming that existing EAP clients implement GTC because it is required by the EAP specification. However, investigations (e.g. [12]) have shown that EAP implementations in general do not support GTC. Hence, the costs of introducing a new EAP method for a particular technology and an profile of GTC for that technology are roughly the same. Thus our decision was based on the technical argument that a new general EAP method for OTP token technology makes for a cleaner design and easier implementation. Furthermore, the method presented herein allows for mutual authentication and establishment of keying material, which GTC does not. To retain the generic nature of GTC, the EAP-POTP method has been designed to support a range of specific OTP algorithms, even though this document also provides a profile of EAP-POTP for RSA SecurID tokens. Nystr÷m Expires August 18, 2005 [Page 5]
Internet-Draft EAP-POTP February 2005 2. Conventions used in this document The key words "MUST", "MUST NOT", "SHALL", "SHOULD", "RECOMMENDED", and "MAY", in this document are to be interpreted as described in RFC 2119 [2]. Nystr÷m Expires August 18, 2005 [Page 6]
Internet-Draft EAP-POTP February 2005 3. Authentication model The EAP-POTP method provides two-factor based user authentication as defined below. Additionally, it may provide mutual authentication (authenticating the EAP server to the EAP client) and establish keying material. There are basically three entities in the authentication method described here: o A client, or "peer", using EAP terminology, acting on behalf of a user possessing an OTP token; o A server, or "authenticator", using EAP terminology, to which the user needs to authenticate; and o A backend authentication server, providing an authentication service to the authenticator. Even though the authenticator in practice may function as a client with respect to the backend authentication server, relaying authentication credentials et cetera as needed, both servers are, unless explicitly mentioned, collectively denoted as "the EAP server" here. When no backend authentication server is used, the authenticator will be the EAP server. When the authenticator operates in pass-through mode, the EAP server is located on the backend authentication server. The protocol used between the authenticator and the backend authentication server is outside the scope of this document, although RADIUS [13] is a typical choice. It is assumed that the EAP client and the peer are located on the same host, and hence only the term "peer" is used in the following for these entities. The EAP-POTP method assumes the use of a shared secret key, or "seed", and a personal identification number (PIN), which are known both by the user and the backend authentication server. The secret seed is stored on an OTP token that the user possesses, as well as on the authentication server. The term "two-factor authentication" stems from the fact that a user needs not only physical access to the token but also knowledge about the PIN in order to perform an authentication. In its most basic variant, the EAP-POTP method provides only one service, namely user authentication where the user provides information to the authentication server, so that the server can authenticate the user. A more advanced variant provides mutual authentication, protection against eavesdropping and establishment of authenticated keying material. Nystr÷m Expires August 18, 2005 [Page 7]
Internet-Draft EAP-POTP February 2005 4. Description of the EAP-POTP method 4.1 Overview Note: Since the EAP-POTP method is general in nature, the term "POTP-X" is used below as a placeholder for an EAP method type identifier, identifying the use of a particular OTP algorithm with EAP-POTP. In the case of using RSA SecurID tokens within EAP-POTP, the EAP method SHALL be 32. A typical EAP-POTP authentication is performed as follows (Appendix A provides more detailed examples): a. The optional EAP Identity Request/Response is exchanged, as per RFC 3748 [1]. An identity provided here alleviates the need for a "User Identifier" or a "Token Serial Number" triplet ("TLV") (defined below) later in the exchange. b. The EAP server sends an EAP-Request of type POTP-X with a Version TLV. The Version TLV indicates the highest and lowest version of this protocol supported by the server. The EAP server typically also includes an OTP TLV in the EAP-Request. The OTP TLV instructs the peer to respond with the current OTP (possibly in protected form), and may contain a challenge and some other information, like server policies. The EAP server may also include a Server-Info TLV in the request, if it supports session resumption. The Server-Info TLV identifies the authentication server, contains an identifier for this (new) session, and may be used by the peer to find an already existing session with the EAP server. c. The peer responds with an EAP-Nak message if it does not support a version of this protocol that is also supported by the server, as indicated in the server's Version TLV. If the peer supports a version of this protocol that is also supported by the EAP Server, the peer generates an EAP-Response of type POTP-X as follows: * First, it generates a Version TLV which indicates the peer's highest supported version. This Version TLV will be part of the EAP-Response to the EAP server. * Next, if the peer's highest supported version equals that of the EAP server, and the EAP server sent a Server-Info TLV, the peer checks if it has a saved session with the EAP server. If an existing session with the server is found, and session resumption is possible (the Server-Info TLV may explicitly disallow it) the peer calculates new session keys and responds with a Resume TLV and the Version TLV. * Otherwise, if the peer's highest supported version equals that of the EAP server, and the received EAP-Request message Nystr÷m Expires August 18, 2005 [Page 8]
Internet-Draft EAP-POTP February 2005 contains an OTP TLV, the peer requests (possibly through user interaction) the OTP token to calculate a one-time password based on the information in the received EAP-Request message (which could, for example, carry a challenge), the current token state (e.g. token time), a shared secret (the "seed"), and a user-provided PIN (note that, depending on the OTP token type, some of the information in the EAP-Request may not be used in the OTP calculation). If the received OTP TLV has the P bit set (see below), the peer then combines the token-provided OTP with other information, and provides the combined data to a key derivation function. The key derivation function generates several keys, of which one is used to calculate a MAC on the received message together with some other information. The resulting MAC together with some additional information is then placed in an OTP TLV (with the P bit set) that is sent in a response to the EAP server together with the Version TLV. If the P bit is not set in the received OTP TLV, the peer instead inserts the calculated OTP value directly in an OTP TLV, which then is sent to the EAP server together with the Version TLV. * Finally, if the peer's highest supported version differs from the server's, or if the server did not provide any TLVs besides the Version TLV in its initial request, the peer just sends back the generated Version TLV as an EAP-Response to the EAP server. d. If the EAP server receives an EAP-Nak message the session negotiation failed and the EAP server may try with another EAP method. Otherwise, the EAP server checks the peer's supported version. If the peer did not support the highest version supported by the server, the server will send a new EAP-Request with TLVs adjusted for that version. Otherwise, and assuming the EAP server did send additional TLVs in its initial EAP-Request, the EAP server will attempt to authenticate the peer based on the response provided in c). Depending on the result of this authentication, the EAP server may either * send a new EAP-Request of type POTP-X to the peer indicating that session resumption was not possible, and ask for a new OTP (this would be the case when the peer responded with a Resume TLV and the session indicated in the Resume TLV was not valid), * send a new EAP-Request of type POTP-X to the peer (e.g. to ask for the next OTP), * accept the authentication (and send an EAP-Request message containing a Confirm TLV to the peer if the received response has the P bit set or was a successful attempt at session resumption, or otherwise send an EAP-Success message to the peer), or Nystr÷m Expires August 18, 2005 [Page 9]
Internet-Draft EAP-POTP February 2005 * fail the authentication (and send an EAP-Failure message - possibly preceded by an EAP-Request message of type Notification (2) - to the peer). e. If the peer receives an EAP-Success or an EAP-Failure message the protocol is finished. If the peer receives an EAP-Request of type Notification it responds as specified by RFC 3748 [1]. If the peer receives an EAP-Request of type POTP-X with a Confirm TLV it attempts to authenticate the EAP server using the provided data. If the authentication is successful the peer responds with an EAP-Response of type POTP-X with a Confirm TLV. If it is unsuccessful, the peer responds with an empty EAP-Response of type POTP-X. If the peer receives an EAP-Request of type POTP-X containing some other TLVs it continues as specified in c) above (though no version negotiation will take place in this case) or as described for those TLVs. f. When an EAP server, which has sent an EAP-Request of type POTP-X with a Confirm TLV receives an EAP-Response of type POTP-X with a Confirm TLV present, it can proceed in one of two ways: If it has detected that the user needs to update the OTP PIN, it will send a New PIN TLV at which point the handshake is back at step c) above (save for the version negotiation). Otherwise it will send an EAP-Success method to the peer to indicate successful protocol completion. At this point the parties shall have calculated a master session key as described in Section 4.4. When an EAP server, which has sent an EAP-Request of type POTP-X with a Confirm TLV receives an EAP-Response of type POTP-X which is empty (i.e. does not contain any TLVs), then it shall respond with an EAP-Failure and terminate the handshake. As implied by the description, steps c) and d) may be carried out a number of times before completion of the exchange. One example of this is when the authentication server initially requests an OTP, accepts the response from the peer, peforms an (intermediary) Confirm TLV exchange, requests the peer to select a new PIN, and finally asks the peer to authenticate with an OTP based on the new PIN (which again will be followed with a final Confirm TLV exchange). Note: The RSA SecurID term for the OTP is "PASSCODE" when the OTP includes a user PIN. Without a user PIN, the RSA SecurID term for the OTP is "tokencode". 4.2 Version negotiation The EAP-POTP method provides a version negotiation mechanism that enables implementations to be backward compatible with previous versions of the protocol. This specification documents the EAP-POTP protocol version 0. Version negotiation proceeds as follows: Nystr÷m Expires August 18, 2005 [Page 10]
Internet-Draft EAP-POTP February 2005 a. In the first EAP-Request of type POTP-X, the EAP server MUST send a Version TLV in which it sets the "Highest supported" version field to its highest supported version number, and the "Lowest supported" version field to its lowest supported version number. The EAP server MAY include other TLV triplets as described below and compatible with the "Highest" supported version number to optimize the number of round-trips in the case of a peer supporting the server's "Highest" version number. b. If the peer supports a version of the protocol that falls within the range of versions indicated by the EAP server, it MUST respond with an EAP-Response of type POTP-X, and containing a Version TLV with the "Highest supported" version field set to the highest version supported by the peer. The peer MUST also respond to any TLV triplets included in the EAP-Request, if it supported the "Highest supported" version indicated in the server's Version TLV. c. The EAP peer MUST respond with an EAP-Nak if the EAP peer does not support a version that falls within the range of versions indicated by the EAP server. This will allow the EAP-Server to use another EAP method for peer authentication. d. When the EAP server receives an EAP-Response containing a Version TLV from the peer, but the "Highest supported" version field in the TLV differs from the "Highest supported" version field sent by the EAP server, or when the version is the same as the one originally proposed by the EAP server, but the EAP server did not include any TLV triplets in the initial request, the EAP server sends a new EAP-Request of type POTP-X with the negotiated version and TLV triplets as desired and described herein. The version negotiation procedure guarantees that the EAP peer and server will agree to the highest version supported by both parties. If version negotiation fails, use of EAP-POTP will not be possible, and another mutually acceptable EAP method will need to be negotiated if authentication is to proceed. The EAP-POTP version field may be modified in transit by an attacker. It is therefore important that EAP entities only accept EAP-POTP versions according to an explicit policy. 4.3 Session resumption This method makes use of session identifiers and server identifiers to allow for improved efficiency in the case where a peer repeatedly attempts to authenticate to an EAP server within a short period of time. This capability is particularly useful for support of wireless roaming. In order to help the peer find a session associated with the EAP Nystr÷m Expires August 18, 2005 [Page 11]
Internet-Draft EAP-POTP February 2005 server, the EAP server MAY send a Server-Info TLV containing a server identifier in its initial EAP-Request of type POTP-X. The identifier may then be used by the peer for lookup purposes. It is left to the peer whether to attempt to continue a previous session, thus shortening the negotiation, or not. Typically the peer's decision will be made based on the time elapsed since the previous authentication attempt to that EAP server. If the peer decides to attempt to resume a session with the EAP server, it sends a Resume TLV identifying the chosen session and other contents as described below to the EAP server. Based on the session identifier chosen by the peer, and the time elapsed since the previous authentication, the EAP server will decide whether to allow the session resumption, or whether to choose a new session. If the EAP server is willing to resume a previously established session, it MUST authenticate the peer based on the contents of the Resume TLV, and, if successful, respond only with a request containing a Confirm TLV. If the Confirm TLV authenticates the authentication server then the peer responds with an empty Confirm TLV, to which the EAP server responds with an EAP-Success message. If the Confirm TLV does not authenticate the server, the peer responds with an empty EAP-Response of type POTP-X. If the authentication of the peer fails, the EAP server MAY send another EAP-Request containing an OTP TLV and a Server-Info TLV with the N bit set to indicate that no session resumption is possible. Sessions MUST NOT be maintained longer than the security of the exchange which created the session permits. E.g. if it is estimated that an attacker will be successful in brute-force searching for the OTP in 10 hours, then EAP-POTP session lifetimes must be less than this value. 4.4 Key derivation The EAP-POTP method described herein makes use of a key derivation function denoted "PBKDF2-SHA256". PBKDF2 is described in [3], Section 5.2. For use with this method, the PBKDF2 PRF SHALL be set to HMAC-SHA256, hence the suffix "-SHA256". HMAC is defined in [4] and SHA-256 is defined in [5]. HMAC-SHA256 is the HMAC construct from [4] with SHA-256 as the hash function H. The output from PBKDF2-SHA256 as described here will consist of four keys: Nystr÷m Expires August 18, 2005 [Page 12]
Internet-Draft EAP-POTP February 2005 o K_MAC, a MAC key used for mutual authentication, o K_ENC, an encryption key used to protect certain data during the authentication, o MSK, a Master Session Key as defined in [1], and o EMSK, an Extended Master Session Key, also as defined in [1]. K_MAC and K_ENC SHALL be 16 octets long, and MSK and EMSK SHALL each be 64 octets long, in conformance with [1]. The "dkLen" parameter from Section 5.2 of [3] shall therefore be set to 160 (the combined length of K_MAC, K_ENC, MSK, and EMSK). The MSK may be used as an ISK_i, for some i, as described in Section 2.5 of [14]. It may also be used as an AAA-Key (see [15]) when setting up security associations between peers, or as a starting point for derivation of MPPE [16] keys (see Appendix B). As described in [1], EMSK is reserved for future use. 4.5 Error handling EAP does not allow for the sending of an EAP-Nak message within a method after the initial EAP-Request and EAP-Response pair of that particular method has been exchanged (see [1], Section 2.1). Instead, when a peer cannot continue an EAP-POTP session either due to the server not being able to authenticate itself or due to some other reason (e.g. user aborting after a New PIN request), the peer MAY respond to an outstanding EAP-Request by sending an empty EAP-Response of type POTP-X rather than immediately terminating the conversation. This allows the EAP server to log the cause of the error. To ensure that the EAP Server receives the empty EAP-Response, the peer SHOULD wait for the EAP-Server to reply before terminating the conversation. The EAP Server MUST reply with an EAP-Failure. 4.6 Slowing down attackers Since OTPs may be relatively short, it is important to slow down an attacker sufficiently so that it is economically unattractive to brute-force search for a OTP given an observed EAP-POTP handshake in protected mode. One way to do this is to do a high number of iterated hashes in the PBKDF2 function. Another is for the client to include a value unknown to the attacker in the hash computation. Whereas a traditional "salt" value normally is sent in the clear, this "pepper" value will not be sent in the clear, but may instead be transferred to the EAP server in encrypted form. In practice, the procedure is as follows: Nystr÷m Expires August 18, 2005 [Page 13]
Internet-Draft EAP-POTP February 2005 a. The EAP server indicates in its OTP TLV whether it supports pepper searching. Additionally, it may indicate to the peer that a new pepper shall be chosen. b. If the peer supports the use of pepper, the peer checks whether it already has established a shared pepper with this server: If it does have a pepper stored for this server, and the server did not indicate that a new pepper shall be generated, then it uses the existing pepper value as specified in Section 4.8.3 below to calculate an OTP TLV response. In this case the iteration count shall be kept to a minimum as the security of the scheme is provided through the pepper and efficiency otherwise is lost. If the peer does not have a pepper stored for this server, but the server indicated support for pepper searching, or the server indicated that a new pepper shall be generated, then the peer generates a random and uniformly distributed pepper of sufficient length (the maximum length supported by the server is provided in the server's OTP TLV), and includes the new pepper in the PBKDF2 computation. If the peer does not have a pepper stored for this server, and the server did not indicate support for pepper searching, then a pepper will not be used in the response computation. c. If the peer does not support the use of pepper then a pepper will not be used in the response computation. d. The EAP server may, in its subsequent Confirm TLV, provide a pepper to the peer for later use. In this case, the pepper will be substantially longer than a peer-chosen pepper, and encrypted with a key derived from the PBKDF2 computation. The above procedure allows for pepper updates to be initiated by either side, e.g. based on policy. Since the pepper can be seen as a MAC key, its lifetime should be limited. An EAP server which is not capable of storing pepper values for each user it is authenticating may still support the use of pepper - the cost for this will be the extra computation time to do pepper searches. This cost is still substantially lower than the cost for an attacker, however, since the server already knows the underlying OTP. 4.7 EAP-POTP packet format A summary of the EAP-POTP packet format is shown below. The fields are transmitted from left to right. Nystr÷m Expires August 18, 2005 [Page 14]
Internet-Draft EAP-POTP February 2005 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Reserved | TLV-based EAP-POTP message.. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 1 - Request 2 - Response Identifier The Identifier field is one octet and aids in matching responses with requests. For a more detailed description of this field, and how to use it, see [1]. Length The Length field is two octets and indicates the length of the EAP packet including the Code, Identifier, Length, Type, Version, Flags, and TLV-based EAP-POTP message fields. Type Identifies use of a particular OTP algorithm with EAP-POTP. For RSA SecurID, the type SHALL be 32. Reserved This octet is reserved for future use. It SHALL be set to zero for this version of the protocol. TLV-based EAP-POTP message This field will contain 0, 1, or more Type-Length-Value triplets defined as follows (this is similar to the EAP-TLV TLVs defined in PEAP [14], and the explanation of the generic fields is borrowed from that document). 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value ... Nystr÷m Expires August 18, 2005 [Page 15]
Internet-Draft EAP-POTP February 2005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 0 - Non-mandatory TLV 1 - Mandatory TLV The mandatory bit in a TLV indicates that if the peer or server does not support the TLV, it MUST send a NAK TLV in response; and all the other TLVs in the message MUST be ignored. If an EAP peer or server finds an unsupported TLV which is marked as non-mandatory (i.e. optional), it MUST NOT send a NAK TLV on this ground only. The mandatory bit does not imply that the peer or server is required to understand the contents of the TLV. The appropriate response to a supported TLV with content that is not understood is defined by the specification of the particular TLV. R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type The following TLV types are defined for use with EAP-POTP: 0 - Reserved for future use 1 - Version 2 - Server-Info 3 - OTP 4 - NAK 5 - New PIN 6 - Confirm 7 - Vendor-Specific 8 - Resume 9 - User Identifier 10 - Token Serial Number 11 - Time Stamp 12 - Counter These TLVs are defined in the following. With the exception of the NAK TLV, a particular TLV type MUST NOT appear more than once in a message of type POTP-X. Nystr÷m Expires August 18, 2005 [Page 16]
Internet-Draft EAP-POTP February 2005 Length The length of the Value field in octets. Value The value of the TLV. 4.8 EAP-POTP TLV objects 4.8.1 Version TLV The Version TLV carries information about the supported EAP-POTP method version. This TLV MUST be present in the initial EAP-Request of type POTP-X from the EAP server. It MUST NOT be present in any subsequent EAP-Request in the session. The version negotiation procedure is described in detail in Section 4.2 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Highest | Lowest | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 1 - Mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 1 Length 3 in EAP-Requests, 2 in EAP-Responses Reserved Nystr÷m Expires August 18, 2005 [Page 17]
Internet-Draft EAP-POTP February 2005 Reserved for future use. This octet MUST be set to zero for this version. Highest This field SHALL be interpreted as an unsigned integer in network byte order representing the highest protocol version supported by the sender. If a value provided by a peer to an EAP server falls between the server's "Highest" and "Lowest" supported version (inclusive) then that value will be the negotiated version for the authentication session. Lowest This field SHALL be interpreted as an unsigned integer in network byte order representing the lowest version acceptable by the EAP server. The field MUST be present in an EAP-Request. The field MUST NOT be present in an EAP Response. A peer SHALL respond to an EAP-Request of type POTP-X with an EAP-Nak message if the peer's highest supported version is lower than the value of this field. This document defines version 0 of the protocol. EAP-Servers shall therefore set the Highest as well as the Lowest field to 0. Peers shall set the Highest field to 0. 4.8.2 Server-Info TLV The Server-Info TLV carries information about the EAP server and the session (when applicable). It provides one piece in the framework for fast session resumption. This TLV MAY be present in the initial EAP-Request of type POTP-X from the EAP server, which also carries an OTP TLV. It MUST NOT be present if the server does not support session resumption. It MUST NOT be present in any other EAP-Requests of type POTP-X or in any EAP-Response packets. This TLV type MUST be supported by all peers conforming to this specification. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |N| Session Identifier ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session Id. | Nonce ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Nystr÷m Expires August 18, 2005 [Page 18]
Internet-Draft EAP-POTP February 2005 | Server Identifier ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 1 - Mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 2 Length 29 Reserved Reserved for future use. All 7 bits MUST be set to zero for this version of this protocol. N The N bit signals that the peer MUST NOT attempt to resume any session it has stored associated with this server. Session Identifier A 4 octets long identifier for the session about to be negotiated. Note that, in the case of session resumption, this session identifier will not be used (the session identifier for the resumed session will continue to be used). Nonce A 16 octets long nonce chosen by the server. During session resumption, this nonce is used to calculate new K_ENC, K_MAC, MSK, and EMSK as specified below. Server Identifier An identifier for the authentication server. The peer MAY use this identifier to search for a stored session associated with this server, or to associate the session to be negotiated with the Nystr÷m Expires August 18, 2005 [Page 19]
Internet-Draft EAP-POTP February 2005 server. The value of the identifier SHOULD be chosen so as to reduce the risk of collisions with other EAP server identifiers as much as possible. One possibility is to use the DNS name of the EAP server. The identifier MAY also be used by the peer to select a suitable key on the OTP token (when there are multiple keys available). The identifier MUST NOT be longer than 128 octets. The identifier SHALL be a UTF-8 encoded string of printable characters (without any terminating NULL character). 4.8.3 OTP TLV Presence of this TLV in a request indicates that the response SHALL include a (possibly protected) OTP. The EAP server MAY provide a challenge to the peer as described below. When present in a response, this TLV carries a (possibly protected) OTP generated by the user's OTP token. This TLV type MUST be supported by all peers and EAP servers conforming to this specification. The OTP TLV MUST NOT be present in an EAP-Request of type POTP-X which contains a New PIN TLV. Further, the OTP TLV MUST NOT be present in an EAP-Response of type POTP-X which contains a Resume TLV. The OTP TLV also MUST NOT be present in an EAP-Response of type POTP-X if the New PIN TLV was present in the EAP-Request which triggered the response. The OTP TLV is defined as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |P|C|N|T|E|R| Pepper Length |Iteration Count| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Iteration Count (cont.) | Auth. Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Authentication Data (cont.)... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 1 - Mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. Nystr÷m Expires August 18, 2005 [Page 20]
Internet-Draft EAP-POTP February 2005 TLV Type 3 Length 7 + length of Authentication Data field Reserved Reserved for future use. All eleven bits SHALL be set to zero (0) for this version. P In an EAP-Request, the P bit indicates that the OTP in the response MUST be protected. Use of this bit also indicates that mutual authentication will take place as well as generation of keying material. It is RECOMMENDED to always set the P bit. If a peer receives an EAP-Request with an OTP TLV that does not have the P bit set, and the peer's policy dictates protected mode, the peer MUST respond with a NAK-TLV. In an EAP-Response, this bit indicates that the provided OTP has been protected (see below). The P bit MUST be set in a response (and hence the OTP MUST be protected) if and only if the EAP-Request which triggered the response contained an OTP TLV with the P bit set. In an 802.1x WLAN environment, the P bit MUST be set, or, alternatively, the EAP-POTP method MUST be carried out inside an authenticated tunnel such as those provided by [14] or [17]. C The C bit carries meaning only when the OTP algorithm in question makes use of server challenges. For other OTP algorithms, the C bit SHALL always be set to zero. In an EAP-Request, the C bit ("Combine") indicates that the OTP SHALL be calculated using both the provided challenge and internal state (e.g. current token time). The OTP SHALL be calculated based only on the provided challenge (and the shared secret) if the C bit is not set and a challenge is present. The returned OTP SHALL always be calculated based on the peer's current state (and the shared secret) if no challenge is present. If the C bit is set but no challenge is provided, the peer SHALL regard the request as invalid and return a NAK TLV in its response. In an EAP response, this bit indicates that the provided OTP has been calculated using a provided challenge and the token state. The C bit MUST be set in a response if and only if the EAP-Request Nystr÷m Expires August 18, 2005 [Page 21]
Internet-Draft EAP-POTP February 2005 which triggered the response contained an OTP TLV with the C bit set and a challenge. This applies even if the OTP token was not capable of including a provided challenge in the OTP calculation. N In an EAP-Request, the N bit, when set, indicates that the OTP to calculate SHALL be based on the next token "state", and not the current one. As an example, for RSA SecurID this means the next time slot. For an event-based token, it could be an OTP calculated based on the next counter value, if used. This bit will normally not be set in initial EAP-Request messages, but may be set in subsequent ones. Further, the N bit carries no meaning in an EAP-Request if a challenge is present and the C bit is not set, and SHALL be set to 0 in this case. Note that, setting the N bit in an EAP-Request will normally advance the internal state of the token. In an EAP-Response, the N bit, when set, indicates that the OTP was calculated based on the next token "state" (as explained above), and not the current one. The N bit MUST be set in a response if and only if the EAP-Request which triggered the response contained an OTP TLV with the N bit set. T The following applies when the EAP method type is RSA SecurID (32). Other OTP algorithms may define other usages of this bit. In an EAP-Request, the T bit, when set, indicates that the OTP to calculate MUST NOT include a user PIN. This bit will usually not be set in initial EAP-Request messages, but may be set in subsequent ones. This bit will normally be set together with the N bit, to request the next RSA SecurID tokencode. In an EAP-Response, the T bit, when set, indicates that the OTP was calculated without the use of a user PIN. The T bit MUST be set in a response if and only if the EAP-Request which triggered the response contained an OTP TLV with the T bit set. E In an EAP-Request, the E bit, when set, indicates that the peer MUST NOT use any stored pepper value associated with this server in the PBKDF2 computation. Rather, it MUST generate a new pepper (if supported by the peer) and/or use the iteration count parameter to protect the OTP (if the server's Max Pepper Length is 0, then the peer MUST rely on the iteration count only to protect the OTP). This bit will usually not be set in initial EAP-Request messages, but may be set in subsequent ones, e.g. if the server upon receipt of an OTP TLV with a pepper identifier detects that Nystr÷m Expires August 18, 2005 [Page 22]
Internet-Draft EAP-POTP February 2005 it does not have a pepper with that identifier in storage. This bit carries no meaning, and MUST be set to zero, when the P bit is not set. In an EAP-Response, the E bit indicates that the response has been calculated using a newly generated pepper. R In an EAP-Request, the R bit ("Repeat"), when set, indicates that the peer SHOULD calculate its response based on the same OTP value as used for the preceeding response. The use case for setting this bit is when the EAP server has received an OTP TLV from the peer protected with a pepper which the server no longer is in possession of. Since the server has not attempted validation of the provided data, there is no need for the EAP peer to retrieve a new OTP value. This bit carries no meaning, and MUST be set to zero, when the E bit is not set. In an EAP-Response, the R bit is never set. Pepper Length This octet SHALL be present if and only if the P bit is set. When present, it SHALL be interpreted as an unsigned integer between 0..255 (inclusive) in network-byte order. In an EAP-Request, the integer represents the maximum length (in bits) of a client-generated pepper the server is prepared to search for. Peers MUST NOT generate peppers longer than this value. If this octet is set to zero, it means the peer MUST NOT generate a pepper for the PBKDF2 calculation. In an EAP-Response, it indicates the length of the used pepper. Iteration Count These four octets SHALL be present if and only if the P bit is set. When present, they SHALL be interpreted as a positive, 4-octets long, integer in network-byte order. In an EAP-Request, the integer represents the maximum iteration count the peer may use in the PBKDF2 computation. Peers MUST NOT use iteration counts higher than this value. In an EAP-Response, it indicates the actual iteration count used. Note regarding the Pepper Length and Iteration Count parameters: A peer MUST compare these policy parameters provided by the EAP server with local policy and MUST NOT continue the handshake if use of the EAP server's suggested parameters would result in a lower security than the client's acceptable policy. If the security given by the EAP server's provided policy parameters surpasses the security level given by the peer's local policy the client SHOULD use the server's Nystr÷m Expires August 18, 2005 [Page 23]
Internet-Draft EAP-POTP February 2005 parameters (subject to reason - active attackers could otherwise mount simple DoS attacks against peers, e.g. by providing unreasonably high values for the iteration count). Note that the server-provided parameters only applies to the case where the peer cannot use or does not have a previously provided server-provided pepper. If a peer cannot continue the handshake due to the server's policy being unacceptable, it MUST return an EAP-Nak message. Authentication Data EAP-Request: In an EAP-Request, the Authentication Data, when present, contains an optional "challenge". The challenge is an optional octet string that SHOULD be uniquely generated for each request it is present in (i.e. it is a "nonce"), and SHOULD be 8 octets or longer when present. To avoid fragmentation (i.e. EAP messages longer than the minimum EAP MTU size), the challenge MUST NOT be longer than 256 octets (see [1]). When the challenge is not present, the OTP will be calculated on the current token state only. The peer MAY ignore a provided challenge if and only if the OTP token the peer is interacting with is not capable of including a challenge in the OTP calculation. In this case, EAP server policies will determine whether to accept a provided OTP value or not. EAP-Response: The following applies to the Authentication Data field in an EAP-Response: When the P bit is set, the peer SHALL populate this field as follows. After the token has calculated the OTP value, the peer SHALL compute: K_MAC | K_ENC | MSK | EMSK = PBKDF2-SHA256(otp, salt | pepper | auth_addr, iteration_count, key_length) where "|" denotes concatenation, "otp" is the already computed and UTF-8 encoded OTP (without any terminating NULL character), "salt" is a nonce 16 octets long, "pepper" is an optional nonce (at most 256 bits long, and if necessary padded to be a multiple of 8 bits long, see below) included to complicate the task of finding a matching "otp" value for an attacker, Nystr÷m Expires August 18, 2005 [Page 24]
Internet-Draft EAP-POTP February 2005 "auth_addr" is an address identifier (at most 32 octets long) for the authenticator (i.e. the network access server, not the backend authentication server, if there is one) as seen by the peer and as specified below, "iteration_count" is an iteration count chosen such that the computation time on the peer is acceptable (based on the server's indicated policy and the client's local policy), while an attacker, having observed the response and initiating a search for a matching OTP will be sufficiently slowed down. The "iteration_count" value MUST be at least 1000 unless a server-provided pepper is being used, in which case it SHOULD be 1. "key_length" is the combined length of the desired key material, in octets. For this version of this method, key_length SHALL be 160. The "pepper" values are only included in PBKDF2 calculations and are never sent in the clear to EAP servers (though the peers do send their length, in bits). The purpose of the pepper values are, as mentioned above, to slow down an attacker's search for a matching OTP, while not slowing down the peer (which iterated hashes do). If the pepper has been generated by the peer and the chosen pepper length in bits is not a multiple of 8 then the pepper value SHALL be padded to the left with '0' bits to the nearest multiple of 8 before being used in the PBKDF2 calculation. This is to ensure the input to the calculation consists only of whole octets. As an example, if the chosen pepper length is four, the pepper value will be padded to the left with four '0' bits to form an octet before being used in the PBKDF2 calculation. When pepper is used, it is RECOMMENDED that the combined entropy of "otp" and "pepper" is at least 128 bits, but note that the iteration count in PBKDF2 also has an impact on the likelihood of a successful brute-force OTP attack, as does the lifetime of the OTP itself. As mentioned previously, a peer MUST NOT include a newly generated pepper value in the PBKDF2 computation if the server did not indicate its support for pepper searching in this session. If the server did not indicate support for pepper searching, then the PBKDF2 computation MUST be carried out with a sufficiently higher number of iterations so as to compensate for the lack of pepper. A server may earlier have transferred a pepper value to the peer in a Confirm TLV (see below). When this is the case, and the peer still have that pepper value stored for this server, the peer MUST NOT generate a new pepper but MUST instead use this transferred pepper value in the PBKDF2 calculations. The only exception to Nystr÷m Expires August 18, 2005 [Page 25]
Internet-Draft EAP-POTP February 2005 this is when a local policy (e.g. timer) dictates that the peer must switch to a new pepper (and the server indicated support for pepper searching). The following applies to the auth_address component: * For dial-up, "auth_addr" SHALL be the phone number called by the peer. The phone number shall be specified in the form of a URL conformant with RFC 2806 ([6]), e.g. "tel:+1234567890". Processing of received phone numbers SHALL be conformant with RFC 2806. * For use with IEEE 802.1X, "auth_addr" SHALL be the MAC address of the authenticator in binary format (6 octets long). * For IP-based EAP, "auth_addr" SHALL be the IPv4 or IPv6 address of the authenticator in binary format (4 respectively 16 octets long). As an example, the IPv4 address "10.129.13.15" would be represented as (in hex) 0A 81 0D 0F, whereas the IPv6 address "0A0A:0B0B:0C0C:0D0D:0E0E:0F0F:1010:1111" would be represented as (in hex) 0A 0A 0B 0B 0C 0C 0D 0D 0E 0E 0F 0F 10 10 11 11. Note: Use of the authenticator's identifying address within the computation aids in protection against man-in-the-middle attacks where a rogue authenticator seeks to intercept and forward the Authentication Data in order to impersonate the peer at a legitimate authenticator (but see also the discussion around spoofed authenticator addresses in the security considerations section). As an example, when otp = "12345678", salt = 0x54434534543445435465768789099880, pepper is not used, auth_addr = "10.129.13.1", iteration_count = 2000, and key_length = 160, the input to the PBKDF2-SHA256 calculation will be (first two parameters in hex, line wrap for readability): (3132333435363738, 54434534543445435465768789099880 | 0a810d01, 2000, 160) K_MAC is the first 16 octets of the output from PBKDF2-SHA256, K_ENC the next 16 octets, MSK the following 64 octets and EMSK the final 64 octets. Using K_MAC, the peer calculates: mac = HMAC-SHA256(K_MAC, msg_hash) where "msg_hash" is the SHA-256 hash of all previous EAP messages of type POTP-X in this exchange as sent and received by the peer and in chronological order (it will typically be the hash of just one message, the EAP server's initial EAP-Request of type POTP-X Nystr÷m Expires August 18, 2005 [Page 26]
Internet-Draft EAP-POTP February 2005 containing the OTP TLV which triggered this response). Re-transmissions are not included in this set of messages. User identifier TLVs MUST NOT be included in the hash (this is to allow for a back-end service which does not know about individual user names), i.e. any such TLV is removed from the message which it appeared in before the message is hashed (the hash shall still be made using the message's original EAP headers and length values - this needs to be taken into account if an intermediate replaces the user identifier with some other value). Note: To save on storage space, each EAP entity may hash messages as they are sent and received. This reduces the amount of state needed for this purpose to the state required for SHA-256. The peer then places the first 16 octets of "mac" in the Authentication Data field, followed by the "salt" value, followed by one octet representing the length of the "auth_addr" value in octets, followed by the actual "auth_addr" value in binary form, optionally followed by a pepper identifier (only when the peer made use of a pepper value previously provided by the EAP server). Pepper identifiers, when present, are always four octets long. All variables SHALL be present in the form they were input to the PBKDF2 algorithm. This will result in the Authentication Data field being 33 + (length of auth_addr in octets) + (4, for pepper identifier, when present) octets long. Continuing the previous example, the Authentication Data field will be populated with (in hex, line wrap for readability): < 16 octets of mac > | 54434534543445435465768789099880 | 04 | 0a810d01 Note: Since in this case (i.e. when the P bit is set) successful authentication of the peer by the EAP server will be followed by the transmission of an EAP-Request of type POTP-X containing a Confirm TLV for mutual authentication, the peer MUST save either all the input parameters to the PBKDF2-SHA256 computation or the keys K_MAC, K_ENC, MSK, and EMSK (recommended, since they will be used later). This is because the peer cannot be guaranteed to be able to generate the same OTP value again. For the same reason (the Confirm-TLV from the EAP server), the peer MUST also store either the SHA-256 hash of the sent EAP-Response or the EAP-Response itself (but see the note above about not including any User Identifier TLVs in the hash computation). Given a set of possible OTP values, the authentication server verifies an authentication request from the peer by computing Nystr÷m Expires August 18, 2005 [Page 27]
Internet-Draft EAP-POTP February 2005 K_MAC' | K_ENC' | MSK' | EMSK' = PBKDF2-SHA256(otp', salt | pepper' | auth_addr, iteration_count, 160) for each possible OTP value otp', and each possible pepper value pepper' and the provided values for salt, authenticator address, and iteration count. If the given pepper length is not a multiple of eight, each tested pepper value will be padded to the left to the nearest multiple of eight, in the same manner as was done by the peer. If the server already shared a secret pepper value with this peer then obviously there will only be one possible pepper value, and the server will find it based on the pepper_identifier provided by the peer. The server SHALL send a new EAP-Request of type POTP-X with an OTP TLV with the E bit set if the peer provided a pepper identifier unknown to the server, and the server does not support pepper searching. For each K_MAC', the EAP server computes mac' = HMAC-SHA256(K_MAC', msg_hash') where msg_hash' is the EAP server's SHA-256 hash of the same messages as the peer calculated its message hash msg_hash on, but this time as sent and received by the EAP server. If the first 16 octets of mac' matches the first 16 octets in the Authentication Data field of the EAP-Response in question, and the provided authenticator address is acceptable, then the peer is authenticated. Note that the EAP server may accept more than one OTP value at a given time, e.g. due to clock drift in the token. See Section 4.4 for details on PBKDF2-SHA256 and HMAC-SHA256. If the authentication was successful, the authentication server then attempts to authenticate itself to the peer by use of the Confirm TLV (see below). When the P bit is not set, the peer SHALL directly place the UTF-8 encoded OTP in the Authentication Data field, without any terminating NULL character. In this case, the EAP server MUST NOT send a Confirm TLV upon successful authentication of the peer (instead, it sends an EAP-Success message). 4.8.4 NAK TLV Presence of this TLV indicates that the peer did not support or accept a received TLV with the M bit set. This TLV may occur 0, 1, or more times in an EAP-Response of type POTP-X. Each occurrence flags the non-support of a particular received TLV. The NAK TLV is sent by peers and MUST be supported by all EAP servers Nystr÷m Expires August 18, 2005 [Page 28]
Internet-Draft EAP-POTP February 2005 conforming to this specification. Receipt of a NAK TLV would normally cause an authentication to fail, and the EAP server to send an EAP-Failure message to the peer. Note: The definition of the NAK TLV herein matches the definition made in [14], and has the same type number. Field descriptions are copied from that document, with some minor modifications. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Id | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NAK-Type | TLVs.... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 1 - Mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 4 Length >= 6 Vendor-Id The Vendor-Id field is four octets, and contains the Vendor-Id of the TLV that was not supported. The high-order octet is 0 and the low-order 3 octets are the SMI Network Management Private Enterprise Code of the Vendor in network byte order. The Vendor-Id field MUST be zero for TLVs that are not Vendor-Specific TLVs. For Vendor-Specific TLVs, the Vendor-ID MUST be set to the SMI code. NAK-Type Nystr÷m Expires August 18, 2005 [Page 29]
Internet-Draft EAP-POTP February 2005 The type of the unsupported TLV. The TLV MUST have been included in the most recently received EAP message. TLVs This field contains a list of TLVs, each of which MUST NOT have the mandatory bit set. These optional TLVs can be used in the future to communicate why the offending TLV was determined to be unsupported. 4.8.5 New PIN TLV Presence of this TLV in a request indicates that the response SHALL include a new user PIN. The EAP server MAY provide a new PIN as described below. When present in a response, the New PIN TLV carries a suggested new user PIN. This TLV may be used by an EAP server when policy dictates that the peer (user) needs to change the OTP PIN. It MUST NOT be sent unless the peer has been authenticated. Further, if the peer was authenticated through the use of an OTP TLV with the P bit set, then any provided PIN from the EAP server, and the PIN sent from the peer, MUST be encrypted with the derived K_ENC key. The New PIN TLV MUST be sent by a peer if and only if the EAP-Request which triggered the response contained a New PIN TLV, and it was valid for the EAP server to send such a TLV, as described. This TLV type MAY be supported by peers and EAP servers conforming to this specification. Profiles will need to specify whether it is mandatory or not. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |Q|A| PIN Length | PIN ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Min. PIN Length|Max. PIN Length| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 0 - Non-mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. Nystr÷m Expires August 18, 2005 [Page 30]
Internet-Draft EAP-POTP February 2005 TLV Type 5 Length >=2 (the PIN may or may not be present.) Reserved Reserved for future use. All six bits SHALL be set to zero for this version. Q The Q bit, when set in an EAP-Request, indicates that an accompanying PIN is required, i.e. the peer (user) is not free to choose another PIN. When the Q bit is set, there MUST be an accompanying PIN and the provided PIN MUST be used in subsequent OTP generations. A peer shall respond with a NAK-TLV if the Q bit is set but there is not any accompanying PIN. When the Q bit is not set, any provided PIN is suggested only, and the peer is free to choose another PIN, subject to local policy. The Q bit carries no meaning, and SHALL be set to zero, in an EAP-Response. A The A bit, when set in an EAP-Request, indicates that the PIN is alphanumeric, i.e. alphanumeric characters are allowed. The A bit carries no meaning, and SHALL be set to zero, in an EAP Response. PIN Length This field shall be interpreted as an unsigned integer in network byte order representing the length of the provided PIN (this implies that the maximum length of a PIN will be 255 octets). PIN In an EAP-Request, subject to the setting of the Q bit, the PIN field MAY be empty. If empty, the peer (user) will need to choose a PIN subject to local and (any) provided policy. When the PIN field is not empty, it MUST consist of UTF-8 [7] encoded printable characters without a terminating NULL character. A provided PIN MUST be encrypted whenever a K_ENC has been calculated in the session, i.e. when the handshake executes in protected mode. The Nystr÷m Expires August 18, 2005 [Page 31]
Internet-Draft EAP-POTP February 2005 encryption algorithm SHALL be AES [8] in CBC mode. A random, 16 byte IV SHALL in this case be used and SHALL constitute the first 16 octets of the PIN field. In an EAP-Response, the PIN value SHALL consist of a (possibly encrypted, see below) UTF-8 encoded string of printable characters. It MUST NOT be NULL-terminated. The PIN value MUST be encrypted whenever a K_ENC has been calculated in the session, i.e. when the handshake executes in protected mode. As for the PIN field in the request, the encryption algorithm SHALL be AES in CBC mode with a random, 16 byte IV, and the IV SHALL in this case constitute the first 16 octets of the PIN field. The peer accepts a PIN suggested by the EAP server by replying with the same PIN, but MAY replace it with another one, depending on whether the Q bit was set or not in the request which triggered the response. The length of the PIN is application-dependent as are any other requirements for the PIN, e.g., allowed characters. The peer MUST be prepared to receive either a message indicating the failure of the authentication using EAP-Notification or a repeated request for a new PIN as described above if the EAP server for some reason does not accept the received PIN. Mechanisms for transferring knowledge about PIN requirements from the EAP server to the peer (beyond those specified for this TLV, such as maximal and minimal PIN length) are outside the scope of this document. However, some information MAY be provided in notification messages transferred from the EAP server to the peer. Min. PIN Length This field MAY be present in an EAP-Request. This field MUST NOT be present in an EAP Response. It shall be interpreted as an unsigned integer in network byte order representing the minimum length allowed for a new PIN. Max. PIN Length This field MUST NOT be present in an EAP-Request unless the Min. PIN Length field is present, in which case it MAY be present. The field MUST NOT be present in an EAP Response. It shall be interpreted as an unsigned integer in network byte order representing the maximum length allowed for a new PIN. This implies that the maximal length for a new PIN is 255 bytes. 4.8.6 Confirm TLV Presence of this TLV in a request indicates that the EAP server has successfully authenticated the peer and now attempts to authenticate itself to the peer. The Confirm TLV MUST NOT appear together with any other TLV in an EAP-Request message of type POTP-X and MUST NOT Nystr÷m Expires August 18, 2005 [Page 32]
Internet-Draft EAP-POTP February 2005 be sent unless the peer has been authenticated through an OTP TLV with the P bit set. Presence of this TLV in a response indicates that the peer successfully authenticated the authentication server. The Confirm TLV MUST be sent in an EAP-Response if and only if the EAP server has been authenticated. If the peer was not able to authenticate the server, then it MUST send an empty (i.e. no TLVs) EAP-Response of type POTP-X. A peer MUST NOT accept an EAP-Success message when it has sent an OTP TLV with the P bit set unless it has received an acceptable Confirm TLV from the EAP server. This TLV type MUST be supported by all peers and EAP servers conforming to this specification. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |C| Authentication Data ... (16 octets) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Pepper Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Encrypted Pepper ... (16 octets) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 1 - Mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 6 Length 17 or 37 in requests, 1 in responses. Reserved Reserved for future use. These seven bits SHALL be set to zero (0) for this version. Nystr÷m Expires August 18, 2005 [Page 33]
Internet-Draft EAP-POTP February 2005 C The C bit, when set in an EAP-Request, indicates that the EAP server intends to send more EAP-Requests of type POTP-X in this session, after receipt of a Confirm TLV from the peer. The C bit carries no meaning, and MUST NOT be set in EAP-Responses. Note: An EAP-Response containing a Confirm TLV will normally be followed by an EAP-Success message from the EAP server concluding the handshake. It MAY however be followed by another EAP-Request from the EAP server, containing e.g. a New PIN TLV. Therefore, peers MUST NOT assume that the only EAP messages following an EAP-Response of type OTP-X containing a Confirm TLV are EAP-Success and EAP-Failure. The C bit gives EAP servers a way to indicate their intent to follow the Confirm TLV with more requests, and allows the peer's state machine to adapt to this. Authentication Data EAP-Request: In a request, this field consists of the first 16 octets of (see also Section 4.8.3): mac_a = HMAC-SHA256(K_MAC', msg_hash2) where "K_MAC'" has been calculated as described in Section 4.8.3 above, and "msg_hash2" is the SHA-256 hash of the OTP TLV of the latest EAP-Response of type POTP-X received from the peer (the one which triggered this request), not including any User Identifier TLV. Given a saved or recomputed value for K_MAC, the peer authenticates the EAP server by computing mac'' = HMAC-SHA256(K_MAC, msg_hash2') where msg_hash2' is the peer's SHA-256 hash of the same EAP-Request as the authentication server calculated it's message hash msg_hash2 on, but this time as it was sent by the peer (and again excluding any User Identifier TLV). If the first 16 octets of mac'' matches the first 16 octets in the Authentication Data field of the EAP-Request in question, then the authentication server is authenticated. Nystr÷m Expires August 18, 2005 [Page 34]
Internet-Draft EAP-POTP February 2005 EAP-Response: Not used in this version, and shall not be present in EAP-Responses. Pepper Identifier In an EAP-Request, the truncated MAC MAY optionally be followed by an encrypted pepper and its identifier. This initial, four octets long, field identifies a pepper generated by the server. This field SHALL NOT be present in EAP-Responses of this version. Encrypted Pepper When present in an EAP-Request, this will be a uniformly distributed and randomly chosen sixteen octets long pepper generated by the EAP server and encrypted with AES in CBC mode using the peer's salt value as IV and K_ENC as the encryption key. EAP servers are RECOMMENDED to include a freshly generated encrypted pepper (and a corresponding Pepper Identifier) in every Confirm TLV. This field SHALL NOT be present in EAP-Responses of this version. When a new pepper was generated by the server and transferred in encrypted form to the peer, then this new pepper value will be stored in the EAP server upon receipt of the Confirm TLV from the peer, and SHOULD be stored with its identifier and associated with the EAP server and the current user in the peer upon receipt of the EAP-Success message. 4.8.7 Vendor-Specific TLV The Vendor-Specific TLV is available to allow vendors to support their own extended attributes not suitable for general usage. A Vendor-Specific-TLV can contain one or more inner TLVs, referred to as Vendor TLVs. The TLV-type of the Vendor-TLV will be defined by the vendor. All the Vendor TLVs inside a single Vendor-Specific TLV SHALL belong to the same vendor. This TLV type may be sent by EAP servers as well as by peers and MUST be supported by all entities conforming to this specification. Conforming implementations may not support specific Vendor TLVs inside a Vendor-Specific TLV however, and MAY in this case respond to the Vendor TLVs with a NAK TLV containing the appropriate Vendor-ID and Vendor TLV type. The presence of a Vendor-Specific TLV in an EAP-Request or EAP-Response of type POTP-X MUST NOT violate any existing rules for Nystr÷m Expires August 18, 2005 [Page 35]
Internet-Draft EAP-POTP February 2005 co-existence of TLVs in such Requests or Responses. If it does, then it will result in an EAP-Failure (when the peer made the violation) or an empty EAP-POTP response (when the EAP-server made the violation). It is left to the definition of specific Vendor-Specific TLVs to further constrain when they are allowed to appear. Note: This TLV type has the same definition and TLV type number as the Vendor-Specific TLV in [14], and the description of it is largely borrowed from that document. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Id | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor TLVs.... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 1 - Mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 7 Length >=4 Vendor-ID The Vendor-Id field is four octets long. The high-order octet SHALL be set to 0 and the low-order 3 octets SHALL be set to the SMI Network Management Private Enterprise Code (see [18]) of the Vendor in network byte order. The Vendor-Id MUST be zero for TLVs that are not Vendor-Specific TLVs. For Vendor-Specific TLVs, the Vendor-ID MUST be set to the SMI code. Vendor TLVs Nystr÷m Expires August 18, 2005 [Page 36]
Internet-Draft EAP-POTP February 2005 This field shall contain vendor-specific TLVs, in a format defined by the vendor. To avoid fragmentation (i.e. EAP messages longer than the minimum EAP MTU size), the field SHOULD NOT be longer than 256 octets. 4.8.8 Resume TLV The Resume TLV MAY be sent by a peer to an authentication server to attempt session resumption. This message MUST only be sent in response to an initial EAP-Request of type OTP-X containing a ServerInfo TLV. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Session Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sess.Id (cont.)| Authentication Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Authentication Data (cont.) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 0 - Non-mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 8 Length 41 Reserved Reserved for future use. This octet SHALL be set to zero (0) for this version. Session Identifier Nystr÷m Expires August 18, 2005 [Page 37]
Internet-Draft EAP-POTP February 2005 A 4 octets long identifier for the session the peer is trying to resume. Authentication Data Upon receipt of the Server-Info TLV, and if the N bit is not set, the peer searches for any stored sessions associated with the server identified by the Server Name field. If a session is found, the peer generates a random 16 octets long nonce, "c_nonce", and calculates: K_MAC | K_ENC | MSK | EMSK = PBKDF2-SHA256(MSK_cur, c_nonce | s_nonce, iteration_count, 160) with notation as for the OTP TLV above, c_nonce being the generated 16 octet long nonce, s_nonce the server nonce from the Server-Info TLV, iteration_count as determined by local policy but MUST be at least 1000, and MSK_cur being the current MSK for the session. The peer then calculates: MAC = HMAC-SHA256(K_MAC, msg_hash) where "msg_hash" is the SHA-256 hash of the EAP server's initial EAP-Request of type POTP-X containing the ServerInfo TLV which allowed session resumption. The peer then places the first 16 octets of the MAC followed by the c_nonce value followed by the iteration count value (as a 4-byte unsigned integer in network byte order) in the Authentication Data field. As an example, when c_nonce = 0x2b3b1b12babdebebfb43bd7bdfbeb8df and iteration_count = 2000, the Authentication Data field will be populated with (in hex, line wrap for readability): < 16 octets of mac > | 2b3b1b12babdebebfb43bd7bdfbeb8df | 000007d0 4.8.9 User Identifier TLV The optional User Identifier TLV carries an identifier, typically the username, for the holder of the OTP token used to generate the OTP. At least one of the User Identifier TLV and the Token Serial Number TLVs MUST be present in the session's first EAP-Response of type POTP-X which also carries the OTP TLV unless a suitable identity has been provided in a preceding EAP-Response of type Identity (1). Use of the User Identifier TLV and/or the Token Serial Number TLV is Nystr÷m Expires August 18, 2005 [Page 38]
Internet-Draft EAP-POTP February 2005 RECOMMENDED even when an EAP-Response of type Identity (1) has been sent earlier. If a peer sends both a User Identifier TLV and a Token Serial Number TLV then the EAP server shall interpret the Token Serial Number TLV as specifying a particular token for the given user. The EAP server MUST respond with an EAP-Failure if it cannot find a token for the provided user. This TLV type is sent by peers and MUST be supported by all EAP servers conforming to this specification. The User Identifier TLV MAY be present in any response. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | User Identifier... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 1 - Mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 9 Length >=1 User Identifier The value SHALL be an UTF-8 encoded string representing the holder of the token (MUST NOT be NULL-terminated). The string MUST be less than 128 octets long. 4.8.10 Token Serial Number TLV The optional Token Serial Number TLV carries an identifier for the token used to generate the OTP. At least one of the User Identifier TLV and the Token Serial Number Nystr÷m Expires August 18, 2005 [Page 39]
Internet-Draft EAP-POTP February 2005 TLVs MUST be present in the session's first EAP-Response of type POTP-X which also carries the OTP TLV unless a suitable identity has been provided in a preceding EAP-Response of type Identity (1). Use of the User Identifier TLV and/or the Token Serial Number TLV is RECOMMENDED even when an EAP-Response of type Identity (1) has been sent earlier. If a peer sends both a User Identifier TLV and a Token Serial Number TLV then the EAP server shall interpret the Token Serial Number TLV as specifying a particular token for the given user. The EAP server MUST respond with an EAP-Failure if it cannot find a token for the provided serial number. This TLV type MUST be supported by all EAP servers conforming to this specification. The Token Serial Number TLV is sent by peers and MAY be present in any response. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Token Serial Number ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 1 - Mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 10 Length >=1 Token Serial Number The token serial number encoded in UTF-8 and without any terminating NULL character. 4.8.11 Time Stamp TLV The optional Time Stamp TLV carries the current token time as Nystr÷m Expires August 18, 2005 [Page 40]
Internet-Draft EAP-POTP February 2005 reported by the token to the peer. In particular, when present in an EAP Response which also carries an OTP TLV, the Time Stamp TLV SHALL reflect the time (again as reported by the token) at which the OTP was calculated. The Time Stamp TLV MAY be used by EAP servers to simplify synchronizations. EAP servers conformant with this specification SHOULD support (i.e. recognize) this TLV, but need not be able to process or act on it. An EAP server that does not support this TLV but receives an EAP-Response with the TLV present MAY ignore the value. The Time Stamp TLV MAY be present in any response. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time Stamp +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 0 - Non-mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 11 Length >= 20 (depending on precision) Time Stamp The time at which the response was generated in the form of a UTF-8 encoded value of the XML simple type "dateTime" with time zone information and precision down to at least seconds. E.g. "2004-06-16T15:20:02Z". 4.8.12 Counter TLV The optional Counter TLV carries the current token counter, when applicable, as reported by the token to the peer. In particular, Nystr÷m Expires August 18, 2005 [Page 41]
Internet-Draft EAP-POTP February 2005 when present in an EAP Response which also carries an OTP TLV, the Counter TLV SHALL reflect the counter value (again as reported by the token) which was used at the OTP calculation. The Counter TLV MAY be used by EAP servers to simplify synchronizations. EAP servers conformant with this specification SHOULD support (i.e. recognize) this TLV, but need not be able to process or act on it. An EAP server that does not support this TLV but receives an EAP-Response with the TLV present MAY ignore the value. The Counter TLV MAY be present in any response. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Counter +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M 0 - Non-mandatory TLV R Reserved for future use. This bit SHALL be set to zero (0) for this version. TLV Type 12 Length >= 20 (depending on precision) Counter The counter value which was current when the response was generated in the form of a UTF-8 encoded string (without any terminating NULL character). Nystr÷m Expires August 18, 2005 [Page 42]
Internet-Draft EAP-POTP February 2005 5. Profile of EAP-POTP for RSA SecurID Besides the following requirements, the requirements on peers and EAP Servers implementing the SecurID profile of EAP-POTP SHALL conform to all basic EAP-POTP normative requirements in this document: o The EAP method type identifier SHALL be 32, o the Counter TLV SHALL NOT be used, o the Time Stamp TLV MUST be supported, o the Resume TLV MUST be supported, o the New PIN TLV MUST be supported, and o the use of the N bit in the OTP TLV SHALL be as described in Section 4.8.3 above. Nystr÷m Expires August 18, 2005 [Page 43]
Internet-Draft EAP-POTP February 2005 6. Security considerations 6.1 Security claims In conformance with RFC 3748 [1], the following security claims are made for the EAP-POTP method: Auth. mechanism: Generic OTP Ciphersuite negotiation: No Mutual authentication: Yes (No in basic variant) Integrity protection: Yes (No in basic variant) Replay protection: Yes (see below) Confidentiality: Only of OTP and new PIN values in P mode Key derivation: Yes (No in basic variant) Key strength: Depends on size of OTP value, strength of underlying shared secret, strength and characteristics of OTP algorithm, pepper length, iteration count, and whether the method is used within a tunnel such as PEAP. Dictionary attack prot.: N/A Fast reconnect: Yes (No in basic variant) Crypt. binding: N/A Session independence: Yes Fragmentation: N/A Channel binding: Yes (No in basic variant) Acknowledged S/F: Yes State Synchronization: Yes (No in basic variant) 6.2 Passive and active attacks In its basic variant (i.e. when the protection of OTPs and mutual authentication is not used), this EAP method only provides protection against passive eavesdropping attacks. It does not provide session privacy, session integrity, server authentication or protection from active attacks. In particular, man-in-the-middle attacks, where an attacker acts as an authenticator in order to acquire a valid OTP are possible. Similarly, the basic variant of this EAP method does not protect against session hijacking taking place after authentication. Nor does it in itself protect against replay attacks, where the attacker gains access by replaying a previous, valid request, but see also the next subsection. When PIN codes are transmitted, they are sent without protection and are also subject to replay attacks. In order to protect against these attacks, the peer MUST only use the Nystr÷m Expires August 18, 2005 [Page 44]
Internet-Draft EAP-POTP February 2005 basic variant of this method over a server-authenticated and (when PIN codes are exchanged) confidentiality-protected connection. This can be achieved via use of, e.g., PEAP [14] or EAP-TTLS [17]. When the OTP protection variant is used however, the EAP method provides privacy for OTPs and new PINs, mutual authentication, and protection against replay attacks. It also provides protection against man-in-the-middle attacks, not due to the infeasibility for a man-in-the-middle to solve for a valid OTP given an OTP TLV, but due to the computational expense of finding the OTP in the limited time period during which it is valid (this is mainly true for tokens including the current time in their OTP calculations). It should be noted, however, that a retrieved OTP, even if "old" and invalid, still may divulge some information about the user's PIN. Clearly this is also true for the basic variant. Implementations of this EAP method are therefore RECOMMENDED to ensure regular user PIN changes, regardless of whether the protected variant or the basic variant is employed. It should also be noted, that while it is possible for a rogue access point e.g. to clone MAC addresses, and hence mount a man-in-the-middle attack, such an access point will not be able to calculate the session keys MSK and EMSK. This demonstrates the importance of using the derived key material to protect a subsequent session. The OTP protection variant also protects against session hijacking, if the derived session key is used (directly or indirectly) to protect a subsequent session. For these reasons, use of the OTP protection variant is RECOMMENDED. It should be noted that not even the OTP protection variant provides privacy for user names and/or token serial numbers however. If privacy for these parameters are required, the EAP-POTP method must be used within a secure tunnel such as those provided by PEAP or TTLS. Authentication server implementations MUST protect against replay attacks, since an attacker could otherwise gain access by replaying a previous, valid request. For time based OTPs, one method to protect against replay attacks is to have the authentication server make a note of the latest authentication time used by the peer (whether sent explicitly by the peer or inferred). A later attempt to authenticate at or before that time will not be permitted. Likewise, if an unusual amount of clock drift in the token is detected, the authentication server SHOULD ask for a new OTP based on the next time interval for the token. For challenge-response based OTPs, a server may use a similar Nystr÷m Expires August 18, 2005 [Page 45]
Internet-Draft EAP-POTP February 2005 technique by encoding the current time in the issued challenge. 6.3 Denial of service attacks An active attacker may replace the iteration count value in OTP TLVs sent by the peer to slow down an authentication server. Authentication servers SHOULD protect against this, e.g. by disregarding OTP TLVs with an iteration count value higher than some pre- or dynamically- (depending on load) set number. 6.4 The use of pepper As described in Section 4.6, the use of pepper will slow down an attacker's search for a matching OTP. The ability to transfer a pepper value in encrypted form from the EAP server to the peer means that, even though there may be an initial computational cost for the EAP server to authenticate the peer, subsequent authentications will be efficient, while at the same time more secure, since a pre-shared, 128 bits long, pepper value will not be easily found by an attacker. An attacker observing an EAP-Request containing an OTP TLV calculated using a pepper chosen by the peer may however, depending on available resources, be able to successfully attack that particular EAP-POTP session, since it most likely will be based on a relatively short pepper value or only an iteration count. Once the correct OTP has been found, eavesdropping on the EAP server's Confirm TLV will potentially give the attacker access to the longer, server-provided pepper for the remaining lifetime of that pepper value. For this reason, initial exchanges with EAP servers SHOULD occur in a secure environment (e.g. in a PEAP tunnel), and if not, the iteration count MUST be significantly higher than for messages where a pre-shared pepper is used. The lifetime of the shared pepper must also be calculated with this in mind. Finally, the pepper value MUST be securely stored by the peer and the EAP server, associated with the user. 6.5 The race attack In the case of fragmentation of EAP messages, it is possible (in the basic variant of this method) for an attacker to listen to most of an OTP, guess the remainder, and then race the legitimate user to complete the authentication. Conforming backend authentication server implementations MUST protect against this race condition. One defense against this attack is outlined below and borrowed from [19]; implementations MAY use this approach or MAY select an alternative defense. Note that the described defense relies on the user providing the identity in response to an initial Identity EAP-Request. Nystr÷m Expires August 18, 2005 [Page 46]
Internet-Draft EAP-POTP February 2005 One possible defense is to prevent a user from starting multiple simultaneous authentication sessions. This means that once the legitimate user has initiated authentication, an attacker would be blocked until the first authentication process has completed. In this approach, a timeout is necessary to thwart a denial of service attack. Nystr÷m Expires August 18, 2005 [Page 47]
Internet-Draft EAP-POTP February 2005 7. IANA considerations This document is a description of a general EAP method for OTP tokens. It also defines EAP method 32 as a profile of the general method. It has no actions for IANA. Nystr÷m Expires August 18, 2005 [Page 48]
Internet-Draft EAP-POTP February 2005 8. Intellectual property considerations RSA Security does not make any claims on the general constructions described in this document. The RSA SecurID technology is covered by a number of US patents (and foreign counterparts), in particular US patent nos. 4,720,860, 4,856,062, 4,885,778, 5,097,505, 5,168,520, and 5,657,388. Additional patents are pending. RSA, RSA Security and SecurID are either registered trademarks or trademarks of RSA Security Inc. in the United States and/or other countries. The names of other products and services mentioned may be the trademarks of their respective owners. Nystr÷m Expires August 18, 2005 [Page 49]
Internet-Draft EAP-POTP February 2005 9. Acknowledgments This document was improved by comments from, and discussion with, a number of RSA Security employees. Simon Josefsson drafted the initial versions of an RSA SecurID EAP method while working for RSA Laboratories. The inspiration for the TLV-type of information exchange comes from PEAPv2. Special thanks to Oliver Tavakoli of Funk Software who has provided numerous useful comments and suggestions. Nystr÷m Expires August 18, 2005 [Page 50]
Internet-Draft EAP-POTP February 2005 10. References 10.1 Normative references [1] Blunk, L., Vollbrecht, J., Aboba, B., Carlson, J. and H. Levkowetz, Ed., "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [3] RSA Laboratories, "Password-Based Cryptography Standard", PKCS #5 v2.0, March 1999. [4] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, February 1997. [5] National Institute of Standards and Technology, "Secure Hash Standard", FIPS 180-2, February 2004. [6] Vaha-Sipila, A., "URLs for Telephone Calls", RFC 2806, April 2000. [7] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [8] National Institute of Standards and Technology, "Specification for the Advanced Encryption Standard (AES)", FIPS 197, November 2001. 10.2 Informative references [9] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", RFC 1661, July 1994. [10] The Institute of Electrical and Electronics Engineers, Inc., "IEEE Standard for Local and metropolitan area networks -- Port-Based Network Access Control", IEEE 802.1X-2001, July 2001. [11] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) Protocol", Work in progress draft-ietf-ipsec-ikev2-17.txt, September 2004. [12] Aboba, B., "Presentation to PPP Extensions WG at 52:th IETF meeting in Salt Lake City", December 2001. [13] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote Dial In User Service (RADIUS)", RFC 2865, June 2000. Nystr÷m Expires August 18, 2005 [Page 51]
Internet-Draft EAP-POTP February 2005 [14] Palekar, A., Simon, D., Zorn, G., Salowey, J., Zhou, H. and S. Josefsson, "Protected EAP Protocol (PEAP) Version 2", Work in progress draft-josefsson-pppext-eap-tls-eap-10.txt, October 2004. [15] Aboba, B., Simon, D., Arkko, J., Eronen, P. and H. Levkowetz, Ed., "EAP Key Management Framework", Work in progress draft-ietf-eap-keying-04.txt, November 2004. [16] Pall, G. and G. Zorn, "Microsoft Point-To-Point Encryption (MPPE) Protocol", RFC 3078, March 2001. [17] Funk, P. and S. Blake-Wilson, "EAP Tunneled TLS Authentication Protocol (EAP-TTLS)", Work in progress draft-ietf-pppext-eap-ttls-05.txt, July 2004. [18] Internet Assigned Numbers Authority, "Private Enterprise Numbers", January 2005. [19] Haller, N., Metz, C., Nesser, P. and M. Straw, "A One-Time Password System", RFC 2289, February 1998. [20] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes", RFC 2548, March 1999. [21] American National Standards Institute, "Information Systems - Coded Character Sets - 7-Bit American National Standard Code for Information Interchange (7-Bit ASCII)", ANSI X3.4, January 1998. [22] Zorn, G., "Deriving Keys for use with Microsoft Point-to-Point Encryption (MPPE)", RFC 3079, March 2001. Author's Address Magnus Nystr÷m RSA Security Email: magnus@rsasecurity.com Nystr÷m Expires August 18, 2005 [Page 52]
Internet-Draft EAP-POTP February 2005 Appendix A. Examples of EAP-POTP exchanges In the examples, "V1","V2","V3", etc. stand for arbitrary values of the correct type. A.1 Basic mode, unilateral authentication This mode should only be used within a secured tunnel. The peer identifies itself with a User Identifier TLV. Peer EAP server <- EAP-Request Type=Identity EAP-Response -> Type=Identity <- EAP-Request Type=OTP-X Version TLV: Highest=0,Lowest=0 OTP TLV: P=0,C=0,N=0,T=0,E=0,R=0 EAP-Response -> Type=OTP-X Version TLV: Highest=0 OTP TLV: P=0,C=0,N=0,T=0,E=0,R=0 Authentication Data=V1 User Identifier TLV: User Identifier=V2 <- EAP-Success A.2 Mutual authentication without session resumption In this case, the peer uses the token serial number in addition to the user identifier. The initial EAP-Identity exchange may also provide user information, or may be restricted to only general domain Nystr÷m Expires August 18, 2005 [Page 53]
Internet-Draft EAP-POTP February 2005 information. Pepper is not used, but will be used in a subsequent session since the server provides the peer with an encrypted pepper in its Confirm TLV. Peer EAP server <- EAP-Request Type=Identity EAP-Response -> Type=Identity <- EAP-Request Type=OTP-X Version TLV: Highest=0,Lowest=0 Server-Info TLV: N=0 Session Identifier=V1 Server Identifier=V2 Nonce=V3 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=0 Iteration Count=V4 EAP-Response -> Type=OTP-X Version TLV: Highest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=0 Iteration Count=V4 Authentication Data=V5 User Identifier TLV: User Identifier=V6 Token Serial Number TLV: Token Serial Number=V7 <- EAP-Request Nystr÷m Expires August 18, 2005 [Page 54]
Internet-Draft EAP-POTP February 2005 Type=OTP-X Confirm TLV: C=0 Authentication Data=V8 Pepper Identifier=V9 Encrypted Pepper=V10 EAP-Response -> Type=OTP-X Confirm TLV: (no data) <- EAP-Success A.3 Mutual authentication with transfer of pepper The difference between this example and the previous one is that the peer makes use of an existing pepper in the PBKDF2 computation. The EAP server provides a new pepper to the peer in the Confirm TLV. Note that the peer had not been able to use a pepper in the response calculation unless it had found the existing pepper, since the server specified a maximum (new) pepper length of zero. Peer EAP server <- EAP-Request Type=Identity EAP-Response -> Type=Identity <- EAP-Request Type=OTP-X Version TLV: Highest=0,Lowest=0 Server-Info TLV: N=0 Session Identifier=V1 Server Identifier=V2 Nonce=V3 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Nystr÷m Expires August 18, 2005 [Page 55]
Internet-Draft EAP-POTP February 2005 Pepper Length=0 Iteration Count=V4 EAP-Response -> Type=OTP-X Version TLV: Highest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V5 Iteration Count=V6 Authentication Data=V7 (includes a pepper identifier) User Identifier TLV: User Identifier=V8 Token Serial Number TLV: Token Serial Number=V9 <- EAP-Request Type=OTP-X Confirm TLV: C=0 Authentication Data=V10 Pepper Identifier=V11 Encrypted Pepper=V12 EAP-Response -> Type=OTP-X Confirm TLV: (no data) <- EAP-Success A.4 Failed mutual authentication This example differs from the previous one in that the peer is not able to authenticate the server. It therefore sends an empty EAP-Response of type POTP-X, which the EAP server acknowledges by responding with an EAP-Failure. Pepper is not used. Peer EAP server Nystr÷m Expires August 18, 2005 [Page 56]
Internet-Draft EAP-POTP February 2005 <- EAP-Request Type=Identity EAP-Response -> Type=Identity <- EAP-Request Type=OTP-X Version TLV: Highest=0,Lowest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V1 Iteration Count=V2 Server-Info TLV: N=0 Session Identifier=V3 Server Identifier=V4 Nonce=V5 EAP-Response -> Type=OTP-X Version TLV: Highest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V1 Iteration Count=V2 Authentication Data=V6 User Identifier TLV: User Identifier=V7 Token Serial Number TLV: Token Serial Number=V8 <- EAP-Request Type=OTP-X Confirm TLV: C=0 Authentication Data=V9 Nystr÷m Expires August 18, 2005 [Page 57]
Internet-Draft EAP-POTP February 2005 EAP-Response -> Type=OTP-X (no data) <- EAP-Failure A.5 Session resumption This example illustrates a successful session resumption. Peer EAP server <- EAP-Request Type=Identity EAP-Response -> Type=Identity <- EAP-Request Type=OTP-X Version TLV: Highest=0,Lowest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V1 Iteration Count=V2 Server-Info TLV: N=0 Session Identifier=V3 Server Identifier=V4 Nonce=V5 EAP-Response -> Type=OTP-X Version TLV: Highest=0 Resume TLV: Session Identifier=V6 (indicating earlier session) Authentication Data=V7 <- EAP-Request Nystr÷m Expires August 18, 2005 [Page 58]
Internet-Draft EAP-POTP February 2005 Type=OTP-X Confirm TLV: C=0 Authentication Data=V8 EAP-Response -> Type=OTP-X Confirm TLV: (no data) <- EAP-Success A.6 Failed session resumption This example illustrates a failed session resumption, followed by a complete mutual authentication. The user is identified through the User Identifier TLV. The client is able to re-use an older pepper. The server sends a new pepper for subsequent use in its Confirm TLV. Peer EAP server <- EAP-Request Type=Identity EAP-Response -> Type=Identity <- EAP-Request Type=OTP-X Version TLV: Highest=0,Lowest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V1 Iteration Count=V2 Server-Info TLV: N=0 Session Identifier=V3 Server Identifier=V4 Nonce=V5 EAP-Response -> Nystr÷m Expires August 18, 2005 [Page 59]
Internet-Draft EAP-POTP February 2005 Type=OTP-X Version TLV: Highest=0 Resume TLV: Session Identifier=V6 (indicating earlier session) Authentication Data=V7 <- EAP-Request Type=OTP-X OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V8 Iteration Count=V9 Server-Info TLV: N=1 (no resumption) Session Identifier=V3 Server Identifier=V4 Nonce=V10 EAP-Response -> Type=OTP-X OTP TLV: P=1,C=0,N=1,T=1,E=0,R=0 Pepper Length=V11 Iteration Count=V12 Authentication Data=V13 (with pepper identifier) User Identifier TLV: User Identifier=V14 <- EAP-Request Type=OTP-X Confirm TLV: C=0 Authentication Data=V15 Pepper Identifier=V16 Encrypted Pepper=V17 EAP-Response -> Type=OTP-X Confirm TLV: (no data) Nystr÷m Expires August 18, 2005 [Page 60]
Internet-Draft EAP-POTP February 2005 <- EAP-Success A.7 Mutual authentication, and new PIN requested. In this example, the user is also requested to select a new PIN. The new PIN is allowed to be alphanumeric, and must be at least 6 characters long. The user selects another PIN than the one suggested by the server. The token is identified through the token serial number. Peer EAP server <- EAP-Request Type=Identity EAP-Response -> Type=Identity <- EAP-Request Type=OTP-X Version TLV: Highest=0,Lowest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V1 Iteration Count=V2 Server-Info TLV: N=0 Session Identifier=V3 Server Identifier=V4 Nonce=V5 EAP-Response -> Type=OTP-X Version TLV: Highest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V6 Iteration Count=V7 Authentication Data=V8 (with pepper identifier) Nystr÷m Expires August 18, 2005 [Page 61]
Internet-Draft EAP-POTP February 2005 User Identifier TLV: User Identifier=V9 Token Serial Number TLV: Token Serial Number=V10 <- EAP-Request Type=OTP-X Confirm TLV: C=1 Authentication Data=V11 EAP-Response -> Type=OTP-X Confirm TLV: (no data) <- EAP-Request Type=OTP-X New PIN TLV: Q=0,A=1 PIN=V12 (encrypted), Min. PIN Length=6 EAP-Response -> Type=OTP-X New PIN TLV: Q=0,A=0 PIN=V13 (encrypted) <- EAP-Request Type=OTP-X OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V1 Iteration Count=V2 EAP-Response -> Type=OTP-X OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V6 Nystr÷m Expires August 18, 2005 [Page 62]
Internet-Draft EAP-POTP February 2005 Iteration Count=V7 Authentication Data=V14 <- EAP-Request Type=OTP-X Confirm TLV: C=0 Authentication Data=V15 EAP-Response -> Type=OTP-X Confirm TLV: (no data) <- EAP-Success A.8 Use of next tokencode mode In this example, the peer is requested to provide a second tokencode to the EAP server. Peer EAP server <- EAP-Request Type=Identity EAP-Response -> Type=Identity <- EAP-Request Type=OTP-X Version TLV: Highest=0,Lowest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V1 Iteration Count=V2 Server-Info TLV: N=0 Session Identifier=V3 Server Identifier=V4 Nonce=V5 Nystr÷m Expires August 18, 2005 [Page 63]
Internet-Draft EAP-POTP February 2005 EAP-Response -> Type=OTP-X Version TLV: Highest=0 OTP TLV: P=1,C=0,N=0,T=0,E=0,R=0 Pepper Length=V6 Iteration Count=V7 Authentication Data=V8 User Identifier TLV: User Identifier=V9 <- EAP-Request Type=OTP-X OTP TLV: P=1,C=0,N=1,T=1,E=0,R=0 Pepper Length=V1 Iteration Count=V2 EAP-Response -> Type=OTP-X OTP TLV: P=1,C=0,N=1,T=1,E=0,R=0 Pepper Length=V6 Iteration Count=V7 Authentication Data=V10 <- EAP-Request Type=OTP-X Confirm TLV: C=0 Authentication Data=V11 EAP-Response -> Type=OTP-X Confirm TLV: (no data) <- EAP-Success Nystr÷m Expires August 18, 2005 [Page 64]
Internet-Draft EAP-POTP February 2005 Appendix B. Use of the MPPE-Send/Receive-Key RADIUS attributes B.1 Introduction This session describes how to populate the MPPE-Send-Key and the MPPE-Receive-Key RADIUS attributes defined in [20] using an MSK established in EAP-POTP. B.2 MPPE key attribute population Once the EAP-POTP MSK has been generated, it is used as follows to populate the MPPE-Send-Key and the MPPE-Receive-Key attributes: Use the initial 32 octets of the MSK as the value for the "Key" sub-fieldin the plaintext "String" field of the MPPE-Send-Key attribute, and use the final 32 octets of the MSK as the "Key" sub-field in the plaintext "String" field of the MPPE-Receive-Key attribute (Note: "Send" and "Receive" here refers to the Authenticator, for the peer they are reversed). Nystr÷m Expires August 18, 2005 [Page 65]
Internet-Draft EAP-POTP February 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Nystr÷m Expires August 18, 2005 [Page 66]
Datatracker
draft-nystrom-eap-potp-00
This is an older version of an Internet-Draft that was ultimately published as RFC 4793.
