Internet Draft David M'Raihi Category: Informational VeriSign Expires: July 9, 2008 Johan Rydell PortWise David Naccache ENS Salah Machani Diversinet Siddharth Bajaj VeriSign January 9, 2008 OCRA: OATH Challenge-Response Algorithms draft-mraihi-mutual-oath-hotp-variants-08.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 9, 2009. Abstract This document describes the OATH algorithm for challenge-response authentication and signatures. This algorithm is based on the HOTP algorithm [RFC4226] that was introduced by OATH (initiative for Open AuTHentication) [OATH] and submitted as an individual draft to the IETF in 2006. OATH-HOTP-VARIANTS Expires - July 2009 [Page 1] OCRA: OATH Challenge Response Algorithms December 2008 Table of Contents 1. Introduction...............................................3 2. Requirements Terminology...................................3 3. Algorithm Requirements.....................................3 4. OCRA Background............................................4 4.1 HOTP Algorithm.............................................4 5. Definition of OCRA.........................................5 5.1 DataInput Parameters........................................5 5.2 CryptoFunction..............................................6 6. The OCRASuite..............................................7 7. Algorithm Modes for Authentication.........................8 7.1 One way Challenge-Response..................................9 7.2 Mutual Challenge-Response..................................10 8. Algorithm Modes for Signature.............................11 8.1 Plain Signature...........................................11 8.2 Signature with Server Authentication......................12 9. Security Considerations...................................13 9.1 Security Analysis of the OCRA algorithm....................14 9.2 Implementation Considerations..............................14 10. IANA Considerations.......................................15 11. Conclusion................................................15 12. Acknowledgements..........................................16 13. References................................................16 13.1 Normative.................................................16 13.2 Informative...............................................16 Appendix A: Source Code........................................17 14. Authors' Addresses........................................24 15. Full Copyright Statement..................................25 OATH-HOTP-VARIANTS Expires - July 2009 [Page 2] OCRA: OATH Challenge Response Algorithms December 2008 1. Introduction OATH has identified several use cases and scenarios that require an asynchronous variant to accommodate users who do not want to maintain a synchronized authentication system. A commonly accepted method for this is to use a challenge-response scheme. Such challenge response mode of authentication is widely adopted in the industry. Several vendors already offer software applications and hardware devices implementing challenge-response - but each of those uses vendor-specific proprietary algorithms. For the benefits of users there is a need for a standardized challenge-response algorithm which allows multi-sourcing of token purchases and validation systems to facilitate the democratization of strong authentication. Additionally, this specification describes the means to create symmetric key based digital signatures. Such signatures are variants of challenge-response mode where the data to be signed becomes the challenge. 2. Requirements Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 3. Algorithm Requirements This section presents the main requirements that drove this algorithm design. A lot of emphasis was placed on flexibility and usability, under the constraints and specificity of the HOTP algorithm and hardware token capabilities. R1 - The algorithm MUST support asynchronous challenge-response based authentication. R2 - The algorithm MUST be capable of supporting symmetric key based digital signatures. Essentially this is a variation of challenge-response where the challenge is derived from the data that need to be signed. R3 - The algorithm MUST be capable of supporting server- authentication, whereby the user can verify that he/she is talking to a trusted server. OATH-HOTP-VARIANTS Expires - July 2009 [Page 3] OCRA: OATH Challenge Response Algorithms December 2008 R4 - The algorithm SHOULD use HOTP [RFC4226] as a key building block. R5 - The length and format of the input challenge SHOULD be configurable. R6 - The output length and format of the generated response SHOULD be configurable. R7 - The challenge MAY be generated with integrity checking (e.g., parity bits). This will allow tokens with pin pads to perform simple error checking when the user enters the challenge value into a token. R8 - There MUST be a unique secret (key) for each token/soft token that is shared between the token and the authentication server. The keys MUST be randomly generated or derived using a key derivation algorithm. R9 - The algorithm MAY enable additional data attributes such as a timestamp or session information to be included in the computation. These data inputs MAY be used individually or all together. 4. OCRA Background OATH introduced the HOTP algorithm as a first open, freely available building block towards strengthening authentication for end-users in a variety of applications. One-time passwords are very efficient at solving specific security issues thanks to the dynamic nature of OTP computations. After carefully analyzing different use cases, OATH came to the conclusion that providing for extensions to the HOTP algorithms was important. A very natural extension is to introduce a challenge mode for computing HOTP values based on random questions. Equally beneficial is being able to perform mutual authentication between two parties, or short-signature computation for authenticating transaction to improve the security of e-commerce applications. 4.1 HOTP Algorithm The HOTP algorithm, as defined in [RFC4226] is based on an increasing counter value and a static symmetric key known only to the prover and verifier parties. As a reminder: HOTP(K,C) = Truncate(HMAC-SHA1(K,C)) OATH-HOTP-VARIANTS Expires - July 2009 [Page 4] OCRA: OATH Challenge Response Algorithms December 2008 Where Truncate represents the function that converts an HMAC-SHA-1 value into an HOTP value. We refer the reader to [RFC4226] for the full description and further details on the rationale and security analysis of HOTP. The present draft describes the different variants based on similar constructions as HOTP. 5. Definition of OCRA OCRA is a generalization of HOTP with variable data inputs not solely based on an incremented counter and secret key values. The definition of OCRA requires a cryptographic function, a key K and a set of DataInput parameters. This section first formally introduces the OCRA algorithm and then introduces the definitions and default values recommended for all parameters. In a nutshell, OCRA = CryptoFunction(K, DataInput) Where: - K: a shared secret key known to both parties; - DataInput: a structure that contains the concatenation of the various input data values defined in details in section 5.1; - CryptoFunction: this is the function performing the OCRA computation from the secret key K and the DataInput material; CryptoFunction is described in details in section 5.2. 5.1 DataInput Parameters This structure is the concatenation over byte array of the OCRASuite value as defined in section 6 with the different parameters used in the computation, save for the secret key K. DataInput = {OCRASuite | 00 | C | Q | P | S | T} where: . OCRASuite is a value representing the suite of operations to compute an OCRA response; . 00 is a byte value used as a separator; . C is an unsigned 8-byte counter value processed high-order bit first, and MUST be synchronized between all parties; It loops around from "{Hex}0" to "{Hex}FFFFFFFFFFFFFFFF" and then starts . over at "{Hex}0"; OATH-HOTP-VARIANTS Expires - July 2009 [Page 5] OCRA: OATH Challenge Response Algorithms December 2008 . Q, mandatory, is a 128-byte list of (concatenated) challenge question(s) generated by the parties; if Q is less than 128 bytes, then it should be padded with zeroes to the right; . P is a 20-byte SHA1-hash of PIN/password that is known to all parties during the execution of the algorithm; . S is a 64-byte UTF-8 encoded string that contains information about the current session; . T is an 8-byte unsigned integer in big endian (i.e. network byte order) representing the number of minutes since midnight UTC of January 1, 1970. More specificatlly, if the OCRA computation includes a timestamp T, you SHOULD first convert your current local time to UTC time (text form). You can then derive the UTC time in milliseconds and T (minutes from Epoch time). When computing a response, the concatenation order is always the following: C | OTHER-PARTY-GENERATED-CHALLENGE-QUESTION | YOUR-GENERATED-CHALLENGE-QUESTION | P| S | T If a value is empty (i.e. a certain input is not used in the computation) then the value is simply not represented in the string. The counter on the token or client MUST be incremented every time a new computation is requested by the user. The server's counter value MUST only be incremented after a successful OCRA authentication. 5.2 CryptoFunction The default CryptoFunction is HOTP-SHA1-6, i.e. the default mode of computation for OCRA is HOTP with the default 6-digit dynamic truncation and a combination of DataInput values as the message to compute the HMAC-SHA1 digest. As indicated in section 5.1, we denote t as the length in digits of the truncation output. For instance, if t = 6, then the output of the truncation is a 6-digit value. We define the HOTP family of functions as an extension to HOTP: - HOTP-H-t: these are the different possible truncated versions of HOTP, using the dynamic truncation method for extracting an HOTP value from the HMAC output; - We will denote HOTP-H-t as the realization of an HOTP function that uses an HMAC function with the hash function H, and the OATH-HOTP-VARIANTS Expires - July 2009 [Page 6] OCRA: OATH Challenge Response Algorithms December 2008 dynamic truncation as described in [RFC 4226] to extract a t- digit value; - t=0 means that no truncation is performed and the full HMAC value is used for authentication purpose. We list the following preferred modes of computation, where * denotes the default CryptoFunction: . HOTP-SHA1-4: HOTP with SHA-1 as the hash function for HMAC and a dynamic truncation to a 4-digit value; this mode is not recommended in the general case but can be useful when a very short authentication code is needed by an application; . *HOTP-SHA1-6: HOTP with SHA-1 as the hash function for HMAC and a dynamic truncation to a 6-digit value; . HOTP-SHA1-8: HOTP with SHA-1 as the hash function for HMAC and a dynamic truncation to an 8-digit value; . HOTP-SHA256-6: HOTP with SHA-256 as the hash function for HMAC and a dynamic truncation to a 6-digit value; . HOTP-SHA512-6: HOTP with SHA-512 as the hash function for HMAC and a dynamic truncation to a 6-digit value; This table summarizes all possible values for the CryptoFunction: Name HMAC Function Used Size of Truncation (t) -------------------------------------------------------------- HOTP-SHA1-t HMAC-SHA1 0 (no truncation), 4-10 HOTP-SHA256-t HMAC-SHA256 0 (no truncation), 4-10 HOTP-SHA512-t HMAC-SHA512 0 (no truncation), 4-10 6. The OCRASuite An OCRASuite value is a text string that captures one mode of operation for the OCRA algorithm, completely specifying the various options for that computation. An OCRASuite value is represented as follows: Algorithm:CryptoFunction:DataInput The client and server need to agree on one or two values of OCRASuite. These values may be agreed at time of token provisioning or for more sophisticated client-server interactions these values may be negotiated for every transaction. Note that for Mutual Challenge-Response or Signature with Server Authentication modes, the client and server will need to agree on two values of OCRASuite - one for server computation and another for client computation. Algorithm OATH-HOTP-VARIANTS Expires - July 2009 [Page 7] OCRA: OATH Challenge Response Algorithms December 2008 --------- Description: Indicates the version of OCRA algorithm. Values: OCRA-v where v represents the version number (e.g. 1, 2 etc.). This document specifies version 1 of the OCRA algorithm. CryptoFunction -------------- Description: Indicates the function used to compute OCRA values Values: Permitted values are described in section 5.2 DataInput --------- Description: This component of the OCRASuite string captures the list of valid inputs for that computation; [] indicates a value is optional: [C] | QFxx | [P | S | T]: Challenge-Response computation [C] | QFxx | [P | T]: Plain Signature computation Each input that is used for the computation is represented by a single letter (except Q) and they are separated by a hyphen. The input for challenge is further qualified by the formats supported by the client for challenge question(s). Supported values can be: Format (F) Up To Length (xx) -------------------------------------------------------------- A (alphanumeric) 04-64 N (numeric) 04-64 H (hexadecimal) 04-64 The default format for challenge question is N08, numeric and upto 8 digits. For example OCRA-1:HOTP-SHA512-8:C-QN08-P means version 1 of the OCRA algorithm with HMAC-SHA512 function, truncated to an 8-digit value, using the counter, a random challenge and a hash of the PIN/Password as parameters. It also indicates that the client supports only numeric challenge upto 8 digits in length. 7. Algorithm Modes for Authentication This section describes the typical modes in which the above defined computation can be used for authentication. OATH-HOTP-VARIANTS Expires - July 2009 [Page 8] OCRA: OATH Challenge Response Algorithms December 2008 7.1 One way Challenge-Response A challenge/response is a security mechanism in which the verifier presents a question (challenge) to the prover who must provide a valid answer (response) to be authenticated. To use this algorithm for a one-way challenge-response, the verifier will communicate a challenge value (typically randomly generated) to the prover. The prover will use the challenge in the computation as described above. The prover then communicates the response to the verifier to authenticate. Therefore in this mode, the typical data inputs will be: C - Counter, optional. Q - Challenge question, mandatory, supplied by the verifier. P - Hashed version of PIN/password, optional. S - Session information, optional T - Timestamp, optional. The diagram below shows the message exchange between the client (prover) and the server (verifier) to complete a one-way challenge- response authentication. It is assumed that the client and server have a pre-shared key K that is used for the computation. CLIENT SERVER (PROVER) (VERIFIER) | | | Verifier sends challenge to prover | | Challenge = Q | |<------------------------------------------| | | | Prover Computes Response | | R = OCRA(K, {[C] | Q | [P | S | T]}) | | Prover sends Response = R | |------------------------------------------>| | | | Verifier Validates Response | | If Response is valid, Server sends OK | | If Response is not, Server sends NOK | |<------------------------------------------| | | OATH-HOTP-VARIANTS Expires - July 2009 [Page 9] OCRA: OATH Challenge Response Algorithms December 2008 7.2 Mutual Challenge-Response Mutual challenge-response is a variation of one-way challenge- response where both the client and server mutually authenticate each other. To use this algorithm, the client will first send a random client- challenge to the server. The server computes the server-response and sends it to the client along with a server-challenge. The client will first verify the server-response to be assured that it is talking to a valid server. It will then compute the client- response and send it to the server to authenticate. The server verifies the client-response to complete the two-way authentication process. In this mode there are two computations: client-response and server-response. There are two separate challenge questions, generated by both parties. We denote these challenge questions Q1 and Q2. Typical data inputs for server-response computation will be: C - Counter, optional. QC - Challenge question, mandatory, supplied by the client. QS - Challenge question, mandatory, supplied by the server. S - Session information, optional. T - Timestamp, optional. Typical data inputs for client-response computation will be: C - Counter, optional. QS - Challenge question, mandatory, supplied by the server. QC - Challenge question, mandatory, supplied by the client. P - Hashed version of PIN/password, optional. S - Session information, optional. T - Timestamp, optional. The following picture shows the messages that are exchanged between the client and the server to complete a two-way mutual challenge- response authentication. It is assumed that the client and server have a pre-shared key K (or pair of keys if using dual-key mode of computation) that is used for the computation. OATH-HOTP-VARIANTS Expires - July 2009 [Page 10] OCRA: OATH Challenge Response Algorithms December 2008 CLIENT SERVER | | | 1. Client sends client-challenge | | QC = Client-challenge | |-------------------------------------------------->| | | | 2. Server computes server-response | | and sends server-challenge | | RS = OCRA(K, [C] | QC | QS | [S | T]) | | QS = Server-challenge | | Response = RS, QS | |<--------------------------------------------------| | | | 3. Client verifies server-response | | and computes client-response | | OCRA(K, [C] | QC | QS | [S | T]) != RS -> STOP | | RC = OCRA(K, [C] | QS | QC | [P | S | T]) | | Response = RC | |-------------------------------------------------->| | | | 4. Server verifies client-response | | OCRA(K, [C] | QS | QC | [P|S|T]) != RC -> STOP | | Response = OK | |<--------------------------------------------------| | | 8. Algorithm Modes for Signature In this section we describe the typical modes in which the above defined computation can be used for digital signatures. 8.1 Plain Signature To use this algorithm in plain signature mode, the server will communicate a signature-challenge value to the client (signer). The signature-challenge is either the data to be signed or derived from the data to be signed using a hash function, for example. The client will use the signature-challenge in the computation as described above. The client then communicates the signature value (response) to the server to authenticate. Therefore in this mode, the data inputs will be: C - Counter, optional. QS - Signature-challenge, mandatory, supplied by the server. P - Hashed version of PIN/password, optional. T - Timestamp, optional. OATH-HOTP-VARIANTS Expires - July 2009 [Page 11] OCRA: OATH Challenge Response Algorithms December 2008 The picture below shows the messages that are exchanged between the client (prover) and the server (verifier) to complete a plain signature operation. It is assumed that the client and server have a pre-shared key K that is used for the computation. CLIENT SERVER (PROVER) (VERIFIER) | | | Verifier sends signature-challenge | | Challenge = QS | |<------------------------------------------| | | | Client Computes Response | | SIGN = OCRA(K, [C] | QS | [P | T]) | | Response = SIGN | |------------------------------------------>| | | | Verifier Validates Response | | Response = OK | |<------------------------------------------| | | 8.2 Signature with Server Authentication This mode is a variation of the plain signature mode where the client can first authenticates the server before generating a digital signature. To use this algorithm, the client will first send a random client- challenge to the server. The server computes the server-response and sends it to the client along with a signature-challenge. The client will first verify the server-response to authenticate that it is talking to a valid server. It will then compute the signature and send it to the server. In this mode there are two computations: client-signature and server-response. Typical data inputs for server-response computation will be: C - Counter, optional. QC - Challenge question, mandatory, supplied by the client. QS - Signature-challenge, mandatory, supplied by the server. T - Timestamp, optional. OATH-HOTP-VARIANTS Expires - July 2009 [Page 12] OCRA: OATH Challenge Response Algorithms December 2008 Typical data inputs for client-signature computation will be: C - Counter, optional. QC - Challenge question, mandatory, supplied by the client. QS - Signature-challenge, mandatory, supplied by the server. P - Hashed version of PIN/password, optional. T - Timestamp, optional. The diagram below shows the messages that are exchanged between the client and the server to complete a signature with server authentication transaction. It is assumed that the client and server have a pre-shared key K (or pair of keys if using dual-key mode of computation) that is used for the computation. CLIENT SERVER | | | 1. Client sends client-challenge | | QC = Client-challenge | |-------------------------------------------------->| | | | 2. Server computes server-response | | and sends signature-challenge | | RS = OCRA(K, [C] | QC | QS | [T]) | | QS = signature-challenge | | Response = RS, QS | |<--------------------------------------------------| | | | 3. Client verifies server-response | | and computes signature | | OCRA(K, [C] | QC | QS | [T]) != RS -> STOP | | SIGN = OCRA( K, [C] | QS | QC | [P | T]) | | Response = SIGN | |-------------------------------------------------->| | | | 4. Server verifies Signature | | OCRA(K, [C] | QS | QC | [P|T]) != SIGN -> STOP | | Response = OK | |<--------------------------------------------------| | | 9. Security Considerations Any algorithm is only as secure as the application and the authentication protocols that implement it. Therefore, this section discusses the critical security requirements that our choice of algorithm imposes on the authentication protocol and validation software. OATH-HOTP-VARIANTS Expires - July 2009 [Page 13] OCRA: OATH Challenge Response Algorithms December 2008 9.1 Security Analysis of the OCRA algorithm The security and strength of this algorithm depends on the properties of the underlying building block HOTP, which is a construction based on HMAC [RFC2104] using SHA-1 as the hash function. The conclusion of the security analysis detailed in [RFC4226] is that, for all practical purposes, the outputs of the dynamic truncation on distinct counter inputs are uniformly and independently distributed strings. The analysis demonstrates that the best possible attack against the HOTP function is the brute force attack. 9.2 Implementation Considerations IC1 - In the authentication mode, the client MUST support two- factor authentication, i.e., the communication and verification of something you know (secret code such as a Password, Pass phrase, PIN code, etc.) and something you have (token). The secret code is known only to the user and usually entered with the Response value for authentication purpose (two-factor authentication). Alternatively, instead of sending something you know to the server, the client may use a hash of the Password or PIN code in the computation itself, thus implicitly enabling two-factor authentication. IC2 - Keys should be of the length of the CryptoFunction output to facilitate interoperability. IC3 - Keys SHOULD be chosen at random or using a cryptographically strong pseudo-random generator properly seeded with a random value. We RECOMMEND following the recommendations in [RFC1750] for all pseudo-random and random generations. The pseudo-random numbers used for generating the keys SHOULD successfully pass the randomness test specified in [CN]. IC4 - Challenge questions SHOULD be 20-byte values and MUST be at least t-byte values where t stands for the digit-length of the OCRA truncation output. IC5 - On the client side, the keys SHOULD be embedded in a tamper resistant device or securely implemented in a software application. Additionally, by embedding the keys in a hardware device, you also have the advantage of improving the flexibility (mobility) of the authentication system. OATH-HOTP-VARIANTS Expires - July 2009 [Page 14] OCRA: OATH Challenge Response Algorithms December 2008 IC6 - We RECOMMEND following the recommendations in [RFC1750] for all pseudo-random and random challenge generations. IC7 - All the communications SHOULD take place over a secure channel e.g. SSL/TLS, IPsec connections. IC8 - The OCRA algorithm when used in mutual authentication mode or in signature with server authentication mode MAY use dual key mode - i.e. there are two keys that are shared between the client and the server. One shared key is used to generate the server response on the server side and to verify it on the client side. The other key is used to create the response or signature on the client side and to verify it on the server side. IC9 - We recommend that implementations MAY use the session information, S as an additional input in the computation. For example, S could be the session identifier from the TLS session. This will enable you to counter certain types of man-in-the-middle attacks. However, this will introduce the additional dependency that first of all the prover needs to have access to the session identifier to compute the response and the verifier will need access to the session identifier to verify the response. IC10 - In the signature mode, whenever the counter or time (defined as optional elements) are not used in the computation, there might be a risk of replay attack and the implementers should carefully consider this issue in the light of their specific application requirements and security guidelines. The server SHOULD also provide whenever possible a mean for the client (if able) to verify the validity of the signature challenge. IC11 - We also RECOMMEND storing the keys securely in the validation system, and more specifically encrypting them using tamper-resistant hardware encryption and exposing them only when required: for example, the key is decrypted when needed to verify an OCRA response, and re-encrypted immediately to limit exposure in the RAM for a short period of time. The key store MUST be in a secure area, to avoid as much as possible direct attack on the validation system and secrets database. Particularly, access to the key material should be limited to programs and processes required by the validation system only. 10. IANA Considerations This document has no actions for IANA. OATH-HOTP-VARIANTS Expires - July 2009 [Page 15] OCRA: OATH Challenge Response Algorithms December 2008 11. Conclusion This draft introduced several variants of HOTP for challenge- response based authentication and short signature-like computations. The OCRASuite provides for an easy integration and support of different flavors within an authentication and validation system. Finally, OCRA should enable mutual authentication both in connected and off-line modes, with the support of different response sizes and mode of operations. 12. Acknowledgements We would like to thank Jeff Burstein, Shuh Chang, Oanh Hoang, Philip Hoyer, Jon Martinsson, Frederik Mennes, Mingliang Pei, Jonathan Tuliani, Stu Vaeth, Enrique Rodriguez and Robert Zuccherato for their comments and suggestions to improve this draft document. 13. References 13.1 Normative [RFC2104] M. Bellare, R. Canetti and H. Krawczyk, "HMAC: Keyed-Hashing for Message Authentication", IETF Network Working Group, RFC 2104, February 1997. [RFC1750] D. Eastlake, 3rd., S. Crocker and J. Schiller, "Randomness Recommendations for Security", IETF Network Working Group, RFC 1750, December 2004. [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3668] S. Bradner, "Intellectual Property Rights in IETF Technology", BCP 79, RFC 3668, February 2004. [RFC4226] D. M'Raihi, M. Bellare, F. Hoornaert, D. Naccache and O. Ranen, "HOTP: An HMAC-based One Time Password Algorithm", IETF Network Working Group, RFC 4226, December 2005. 13.2 Informative [BCK] M. Bellare, R. Canetti and H. Krawczyk, "Keyed Hash Functions and Message Authentication", Proceedings of OATH-HOTP-VARIANTS Expires - July 2009 [Page 16] OCRA: OATH Challenge Response Algorithms December 2008 Crypto'96, LNCS Vol. 1109, pp. 1-15. [OATH] Initiative for Open AuTHentication http://www.openauthentication.org [CN] J.S. Coron and D. Naccache, "An accurate evaluation of Maurer's universal test" by Jean-Sebastien Coron and David Naccache In Selected Areas in Cryptography (SAC '98), vol. 1556 of Lecture Notes in Computer Science, S. Tavares and H. Meijer, Eds., pp. 57-71, Springer- Verlag, 1999 Appendix A: Source Code import java.lang.reflect.UndeclaredThrowableException; import java.security.GeneralSecurityException; import javax.crypto.Mac; import javax.crypto.spec.SecretKeySpec; import java.math.BigInteger; /** * This an example implementation of the OATH OCRA algorithm. * Visit www.openauthentication.org for more information. * * @author Johan Rydell, PortWise */ public class OCRA { private OCRA() {} /** * This method uses the JCE to provide the crypto * algorithm. * HMAC computes a Hashed Message Authentication Code with the * crypto hash algorithm as a parameter. * * @param crypto the crypto algorithm (HmacSHA1, HmacSHA256, * HmacSHA512) * @param keyBytes the bytes to use for the HMAC key * @param text the message or text to be authenticated. */ public static byte[] hmac_sha1(String crypto, byte[] keyBytes, byte[] text) { try { Mac hmac; hmac = Mac.getInstance(crypto); SecretKeySpec macKey = new SecretKeySpec(keyBytes, "RAW"); hmac.init(macKey); return hmac.doFinal(text); OATH-HOTP-VARIANTS Expires - July 2009 [Page 17] OCRA: OATH Challenge Response Algorithms December 2008 } catch (GeneralSecurityException gse) { throw new UndeclaredThrowableException(gse); } } private static final int[] DIGITS_POWER // 0 1 2 3 4 5 6 7 8 = {1,10,100,1000,10000,100000,1000000,10000000,100000000 }; /** * This method generates an OCRA HOTP value for the given * set of parameters. * * @param ocraSuite the OCRA Suite * @param key the shared secret, HEX encoded * @param counter the counter that changes on a * per use basis, HEX encoded * @param question the challenge question * @param password a password that can be used * @param sessionInformation Static information * that identifies the * current session * @param timeStamp a value that reflects a time * * @return A numeric String in base 10 that includes * {@link truncationDigits} digits */ static public String generateOCRA(String ocraSuite, String key, String counter, String question, String password, String sessionInformation, String timeStamp) { int codeDigits = 0; String crypto = ""; String result = null; int ocraSuiteLength = ocraSuite.length(); int counterLength = 0; int questionLength = 0; int passwordLength = 0; int sessionInformationLength = 0; int timeStampLength = 0; if(ocraSuite.toLowerCase().indexOf("sha1") > 1) crypto = "HmacSHA1"; if(ocraSuite.toLowerCase().indexOf("sha256") > 1) crypto = "HmacSHA256"; if(ocraSuite.toLowerCase().indexOf("sha512") > 1) crypto = "HmacSHA512"; OATH-HOTP-VARIANTS Expires - July 2009 [Page 18] OCRA: OATH Challenge Response Algorithms December 2008 // How many digits should we return String oS = ocraSuite.substring(ocraSuite.indexOf(":"), ocraSuite.indexOf(":", ocraSuite.indexOf(":") + 1)); codeDigits = Integer.decode(oS.substring (oS.lastIndexOf("-")+1, oS.length())); // The size of the byte array message to be encrypted // Counter if(ocraSuite.toLowerCase().indexOf(":c") > 1) { counterLength=8; } // Question if((ocraSuite.toLowerCase().indexOf(":q") > 1) || (ocraSuite.toLowerCase().indexOf("-q") > 1)) { questionLength=128; } // Password if((ocraSuite.toLowerCase().indexOf(":p") > 1) || (ocraSuite.toLowerCase().indexOf("-p") > 1)){ passwordLength=20; } // sessionInformation if((ocraSuite.toLowerCase().indexOf(":s") > 1) || (ocraSuite.toLowerCase().indexOf("-s", ocraSuite.indexOf(":", ocraSuite.indexOf(":") + 1)) > 1)){ sessionInformationLength=64; } // TimeStamp if((ocraSuite.toLowerCase().indexOf(":t") > 1) || (ocraSuite.toLowerCase().indexOf("-t") > 1)){ timeStampLength=8; } // Remember to add "1" for the "00" byte delimiter byte[] msg = new byte[ocraSuiteLength + counterLength + questionLength + passwordLength + sessionInformationLength + timeStampLength + 1]; // Put the bytes of "ocraSuite" parameters // into the message byte[] bArray = ocraSuite.getBytes(); for(int i = 0; i < bArray.length; i++){ msg[i] = bArray[i]; } OATH-HOTP-VARIANTS Expires - July 2009 [Page 19] OCRA: OATH Challenge Response Algorithms December 2008 // Put the bytes of "Counter" to the message // Input is HEX encoded if(counter.length() > 0 ){ bArray = new BigInteger(counter,16).toByteArray(); if(bArray.length == 9){ // First byte is the "sign" byte for (int i = 0; i < 8 && i < bArray.length ; i++) { msg[i + 8 - bArray.length + ocraSuiteLength + 1] = bArray[i+1]; } } else { for (int i = 0; i < 8 && i < bArray.length ; i++) { msg[i + 8 - bArray.length + ocraSuiteLength + 1] = bArray[i]; } } } // Put the bytes of "question" to the message // Input is text encoded if(question.length() > 0 ){ bArray = question.getBytes(); for (int i = 0; i < 128 && i < bArray.length ; i++) { msg[i + ocraSuiteLength + 1 + counterLength] = bArray[i]; } } // Put the bytes of "password" to the message // Input is HEX encoded if(password.length() > 0){ bArray = new BigInteger(password,16).toByteArray(); if(bArray.length == 21){ // First byte is the "sign" byte for (int i = 0; i < 20 && i < bArray.length ; i++) { msg[i + ocraSuiteLength + 1 + counterLength + questionLength] = bArray[i+1]; } } else { for (int i = 0; i < 20 && i < bArray.length ; i++) { msg[i + ocraSuiteLength + 1 + counterLength + questionLength] = bArray[i]; } } } OATH-HOTP-VARIANTS Expires - July 2009 [Page 20] OCRA: OATH Challenge Response Algorithms December 2008 // Put the bytes of "sessionInformation" to the message // Input is text encoded if(sessionInformation.length() > 0 ){ bArray = sessionInformation.getBytes(); for (int i = 0; i < 128 && i < bArray.length ; i++) { msg[i + ocraSuiteLength + 1 + counterLength + questionLength + passwordLength] = bArray[i]; } } // Put the bytes of "time" to the message // Input is text value of minutes if(timeStamp.length() > 0){ bArray = new BigInteger(timeStamp,16).toByteArray(); if(bArray.length == 9){ // First byte is the "sign" byte for (int i = 0; i < 8 && i < bArray.length ; i++) { msg[i + 8 - bArray.length + ocraSuiteLength + 1 + counterLength + questionLength + passwordLength + sessionInformationLength] = bArray[i+1]; } } else { for (int i = 0; i < 8 && i < bArray.length ; i++) { msg[i + 8 - bArray.length + ocraSuiteLength + 1 + counterLength + questionLength + passwordLength + sessionInformationLength] = bArray[i]; } } } byte[] hash; bArray = new BigInteger(key,16).toByteArray(); if(bArray[0] == 0){ byte[] b = new byte[bArray.length - 1]; for(int i = 0 ; i < b.length; i++) b[i]=bArray[i+1]; hash = hmac_sha1(crypto, b, msg); } else{ // compute hmac hash hash = hmac_sha1(crypto, bArray, msg); } // put selected bytes into result int int offset = hash[hash.length - 1] & 0xf; int binary = ((hash[offset] & 0x7f) << 24) | ((hash[offset + 1] & 0xff) << 16) OATH-HOTP-VARIANTS Expires - July 2009 [Page 21] OCRA: OATH Challenge Response Algorithms December 2008 |((hash[offset + 2] & 0xff) << 8) | (hash[offset + 3] & 0xff); int otp = binary % DIGITS_POWER[codeDigits]; result = Integer.toString(otp); while (result.length() < codeDigits) { result = "0" + result; } return result; } } Appendix B: Test Vectors OCRA Test Vectors (OCRA Test Vectors generated on March 29, 2008) For all computations, Key (K) = 12345678901234567890 ***** OCRA-V1 Plain Challenge Response ***** ==> Q only, Digit (D) = 6, Algorithm (A) = HMACSHA1 ID OCRASuite Question(Q) OCRA(O) T1.1 OCRA-1:HOTP-SHA1-6:QN08 00000000 713673 T1.2 OCRA-1:HOTP-SHA1-6:QN08 11111111 640542 T1.3 OCRA-1:HOTP-SHA1-6:QN08 22222222 434144 T1.4 OCRA-1:HOTP-SHA1-6:QN08 33333333 024883 T1.5 OCRA-1:HOTP-SHA1-6:QN08 44444444 473006 T1.6 OCRA-1:HOTP-SHA1-6:QN08 55555555 911781 T1.7 OCRA-1:HOTP-SHA1-6:QN08 66666666 059218 T1.8 OCRA-1:HOTP-SHA1-6:QN08 77777777 175339 T1.9 OCRA-1:HOTP-SHA1-6:QN08 88888888 478461 T1.10 OCRA-1:HOTP-SHA1-6:QN08 99999999 681743 ==> Q and P = 1234, Digit (D) = 8, Algorithm (A) = HMACSHA256 ID OCRASuite Question(Q) OCRA(O) T2.1 OCRA-1:HOTP-SHA256-8:QN08-P 00000000 98280381 T2.2 OCRA-1:HOTP-SHA256-8:QN08-P 11111111 77892831 T2.3 OCRA-1:HOTP-SHA256-8:QN08-P 22222222 11994562 T2.4 OCRA-1:HOTP-SHA256-8:QN08-P 33333333 62731746 T2.5 OCRA-1:HOTP-SHA256-8:QN08-P 44444444 27309033 T2.6 OCRA-1:HOTP-SHA256-8:QN08-P 55555555 16123184 T2.7 OCRA-1:HOTP-SHA256-8:QN08-P 66666666 29679588 T2.8 OCRA-1:HOTP-SHA256-8:QN08-P 77777777 86592637 T2.9 OCRA-1:HOTP-SHA256-8:QN08-P 88888888 65897507 T2.10 OCRA-1:HOTP-SHA256-8:QN08-P 99999999 58356750 OATH-HOTP-VARIANTS Expires - July 2009 [Page 22] OCRA: OATH Challenge Response Algorithms December 2008 ==> C & Q, Digit (D) = 8, Algorithm (A) = HMACSHA512 ID OCRASuite Question(Q) Counter(C) OCRA(O) T3.1 OCRA-1:HOTP-SHA512-8:C-QN08 00000000 0 86391474 T3.2 OCRA-1:HOTP-SHA512-8:C-QN08 11111111 1 05308362 T3.3 OCRA-1:HOTP-SHA512-8:C-QN08 22222222 2 71230448 T3.4 OCRA-1:HOTP-SHA512-8:C-QN08 33333333 3 24744363 T3.5 OCRA-1:HOTP-SHA512-8:C-QN08 44444444 4 51162507 T3.6 OCRA-1:HOTP-SHA512-8:C-QN08 55555555 5 69873452 T3.7 OCRA-1:HOTP-SHA512-8:C-QN08 66666666 6 67398361 T3.8 OCRA-1:HOTP-SHA512-8:C-QN08 77777777 7 78278396 T3.9 OCRA-1:HOTP-SHA512-8:C-QN08 88888888 8 13228238 T3.10 OCRA-1:HOTP-SHA512-8:C-QN08 99999999 9 40655008 ==> Q & T, Digit (D) = 8, Algorithm (A) = HMACSHA512, Time (T) Mar 25 2008, 12:06:30 PM ie. OCRATime = 20107866 ***** ID OCRASuite Question(Q) OCRA(O) T4.1 OCRA-1:HOTP-SHA512-8:QN08-T 00000000 83093542 T4.2 OCRA-1:HOTP-SHA512-8:QN08-T 11111111 90956975 T4.3 OCRA-1:HOTP-SHA512-8:QN08-T 22222222 79746883 T4.4 OCRA-1:HOTP-SHA512-8:QN08-T 33333333 93368550 T4.5 OCRA-1:HOTP-SHA512-8:QN08-T 44444444 12212433 T4.6 OCRA-1:HOTP-SHA512-8:QN08-T 55555555 02514283 T4.7 OCRA-1:HOTP-SHA512-8:QN08-T 66666666 25817828 T4.8 OCRA-1:HOTP-SHA512-8:QN08-T 77777777 52087425 T4.9 OCRA-1:HOTP-SHA512-8:QN08-T 88888888 26000130 T4.10 OCRA-1:HOTP-SHA512-8:QN08-T 99999999 66638242 ***** OCRA-V1 Mutual Challenge/Response, Digit (D) = 8, Algorithm (A) = HMACSHA256 ***** ID OCRASuite Question(Q) OCRA(O) T5.1 OCRA-1:HOTP-SHA256-8:QA08 CLI22220SRV11110 25876570 T5.2 OCRA-1:HOTP-SHA256-8:QA08 SRV11110CLI22220 65475908 T5.3 OCRA-1:HOTP-SHA256-8:QA08 CLI22221SRV11111 68337907 T5.4 OCRA-1:HOTP-SHA256-8:QA08 SRV11111CLI22221 36352242 T5.5 OCRA-1:HOTP-SHA256-8:QA08 CLI22222SRV11112 51935447 T5.6 OCRA-1:HOTP-SHA256-8:QA08 SRV11112CLI22222 20036871 T5.7 OCRA-1:HOTP-SHA256-8:QA08 CLI22223SRV11113 12325872 T5.8 OCRA-1:HOTP-SHA256-8:QA08 SRV11113CLI22223 58392008 T5.9 OCRA-1:HOTP-SHA256-8:QA08 CLI22224SRV11114 50478153 T5.10 OCRA-1:HOTP-SHA256-8:QA08 SRV11114CLI22224 53668312 ***** OCRA-V1 Mutual Challenge/Response with Client PIN = 1234 ***** ID OCRASuite Question(Q) OCRA(O) T6.1 OCRA-1:HOTP-SHA512-8:QA08 CLI22220SRV11110 22014886 T6.2 OCRA-1:HOTP-SHA512-8:QA08-P SRV11110CLI22220 55542963 T6.3 OCRA-1:HOTP-SHA512-8:QA08 CLI22221SRV11111 52086443 T6.4 OCRA-1:HOTP-SHA512-8:QA08-P SRV11111CLI22221 54291950 T6.5 OCRA-1:HOTP-SHA512-8:QA08 CLI22222SRV11112 77303083 T6.6 OCRA-1:HOTP-SHA512-8:QA08-P SRV11112CLI22222 39425683 T6.7 OCRA-1:HOTP-SHA512-8:QA08 CLI22223SRV11113 39015190 OATH-HOTP-VARIANTS Expires - July 2009 [Page 23] OCRA: OATH Challenge Response Algorithms December 2008 T6.8 OCRA-1:HOTP-SHA512-8:QA08-P SRV11113CLI22223 38936793 T6.9 OCRA-1:HOTP-SHA512-8:QA08 CLI22224SRV11114 03327937 T6.10 OCRA-1:HOTP-SHA512-8:QA08-P SRV11114CLI22224 89550664 ***** OCRA-V1 Plain Signature (a) no time stamp, Digit (D) = 8, Algorithm (A) = HMACSHA256 ***** ID OCRASuite Question(Q) OCRA(O) T7.1 OCRA-1:HOTP-SHA256-8:QA08 SIG10000 90869451 T7.2 OCRA-1:HOTP-SHA256-8:QA08 SIG11000 12253571 T7.3 OCRA-1:HOTP-SHA256-8:QA08 SIG12000 13568297 T7.4 OCRA-1:HOTP-SHA256-8:QA08 SIG13000 96520389 T7.5 OCRA-1:HOTP-SHA256-8:QA08 SIG14000 57061117 T7.6 OCRA-1:HOTP-SHA256-8:QA08 SIG15000 31653201 T7.7 OCRA-1:HOTP-SHA256-8:QA08 SIG16000 87506781 T7.8 OCRA-1:HOTP-SHA256-8:QA08 SIG17000 25237541 T7.9 OCRA-1:HOTP-SHA256-8:QA08 SIG18000 48988608 T7.10 OCRA-1:HOTP-SHA256-8:QA08 SIG19000 79070512 ***** OCRA-V1 Plain Signature (b) with timestamp Time (T), Mar 25 2008, 12:06:30 PM, OCRATime = 20107866 ***** ID OCRASuite Question(Q) OCRA(O) T8.1 OCRA-1:HOTP-SHA512-8:QA10-T SIG1000000 00051074 T8.2 OCRA-1:HOTP-SHA512-8:QA10-T SIG1100000 85317316 T8.3 OCRA-1:HOTP-SHA512-8:QA10-T SIG1200000 67561993 T8.4 OCRA-1:HOTP-SHA512-8:QA10-T SIG1300000 99207637 T8.5 OCRA-1:HOTP-SHA512-8:QA10-T SIG1400000 81467939 T8.6 OCRA-1:HOTP-SHA512-8:QA10-T SIG1500000 53960486 T8.7 OCRA-1:HOTP-SHA512-8:QA10-T SIG1600000 13472538 T8.8 OCRA-1:HOTP-SHA512-8:QA10-T SIG1700000 03719182 T8.9 OCRA-1:HOTP-SHA512-8:QA10-T SIG1800000 20840783 T8.10 OCRA-1:HOTP-SHA512-8:QA10-T SIG1900000 39923448 Notes: 1. Computations are done on March 21, 2008 based on the OCRA specification draft-mraihi-mutual-oath-hotp-variants-07.txt 2. OCRA Time calculations: Local Time "Mar 25 2008, 12:06:30 PM" at "America/Los_Angeles" time zone (local OCRAtime=20107446) is converted (with time zone plus daylight time savings) to UTC Time "Mar 25 2008, 19:06:30 PM" at "GMT" time zone (UTC OCRAtime=20107866) 3. OCRA Time is treated the same as Counter of 8-byte long value with big-endian order and no base64 encoding. OATH-HOTP-VARIANTS Expires - July 2009 [Page 24] OCRA: OATH Challenge Response Algorithms December 2008 14. Authors' Addresses Primary point of contact (for sending comments and question): David M'Raihi VeriSign, Inc. 685 E. Middlefield Road Phone: 1-650-426-3832 Mountain View, CA 94043 USA Email: dmraihi@verisign.com Other Authors' contact information: Johan Rydell Portwise, Inc. 275 Hawthorne Ave, Suite 119 Phone: 1-650-515-3569 Palo Alto, CA 94301 USA Email: johan.rydell@portwise.com David Naccache ENS, DI 45 rue d'Ulm Phone: +33 6 16 59 83 49 75005, Paris France Email: david.naccache@ens.fr Salah Machani Diversinet Corp. 2225 Sheppard Avenue East Suite 1801 Toronto, Ontario M2J 5C2 Phone: 1-416-756-2324 Ext. 321 Canada Email: smachani@diversinet.com Siddharth Bajaj VeriSign, Inc. 487 E. Middlefield Road Phone: 1-650-426-3458 Mountain View, CA 94043 USA Email: sbajaj@verisign.com 15. Full Copyright Statement Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. 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