Internet Draft David M'Raihi
VeriSign
Category: Johan Rydell
Informational PortWise
Document: David Naccache
draft-mraihi-mutual-oath-hotp-variants-04.txt ENS
Salah Machani
Diversinet
Siddharth Bajaj
VeriSign
Expires:
April 2007 October 2006
OCRA: OATH Challenge-Response Algorithms
Status of this Memo
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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 last year.
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OCRA: OATH Challenge Response Algorithms September 2006
Table of Contents
1. Introduction...............................................3
2. Requirements Terminology...................................3
3. Algorithm Requirements.....................................3
4. OCRA Background............................................4
4.1 HOTP Algorithm.............................................4
4.2 OCRA Algorithm.............................................5
5. Definition of OCRA.........................................5
5.1 DataInput Parameters........................................6
5.2 CryptoFunction..............................................6
6. The OCRASuite..............................................7
7. Algorithm Modes for Authentication.........................8
7.1. One way Challenge-Response.................................8
7.2. Response Only (OTP) Mode...................................9
7.3. 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...................................14
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: Code Source........................................17
Appendix B: Test Vectors.......................................19
14. Authors' Addresses........................................21
15. Full Copyright Statement..................................22
16. Intellectual Property.....................................22
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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. The 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 we need a standardized challenge-response algorithm to
allow multi-sourcing of token purchases and validation systems to
facilitate the democratization of strong authentication.
Additionally, this specification can also be used to create
symmetric key based digital signatures. Such systems 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 needs 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 valid server.
R4 - The algorithm SHOULD use HOTP [RFC4226] as a key building
block.
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R5 - The length and format for the input challenge SHOULD be
configurable.
R6 - The output length and format for the 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 if the user enters the value into a token.
R8 - There MUST be a fixed randomly generated secret (key) for each
token/soft token that is shared between the token and the
authentication server.
R9 - The algorithm MUST enable additional data attributes such as a
counter, a time function 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 toward hardening 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, being able to perform mutual authentication between two
parties, or short-signature computation for authenticating
transaction was also identified as critical for improving the
security of e-commerce applications.
This section summarizes the HOTP algorithm and then, formally
introduces the OCRA algorithm.
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))
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Where Truncate represents the function that converts an HMAC-SHA-1
value into an HOTP value.
The Key (K), the Counter (C) and Data values are hashed high-order
byte first. The HOTP values generated by the HOTP generator are
treated as big endian.
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.
4.2 OCRA Algorithm
In a nutshell, OCRA is a generalization of HOTP with variable data
inputs not solely based on an incremented counter and secret key
values.
OCRA = CryptoFunction(K, DataInput)
Where:
- K: a shared secret key known to both parties;
- CryptoFunction: this is the function performing the OCRA
computation from the secret key K and DataInput material;
CryptoFunction is described in details in section 5.2;
- DataInput: a structure that contains the concatenation of the
various input data values. Defined in details in section 5.1.
5. Definition of OCRA
The definition of OCRA requires a cryptographic function, a key K
and a set of DataInput parameters. This section introduces these
definitions and default value recommended for all the parameters.
We denote L as the byte-length of the CryptoFunction output. For
instance, if CryptoFunction was SHA-1, then L = 20.
We denote B as the byte-length of the blocks manipulated by the
core function internally. For instance if CryptoFunction was HMAC-
SHA-1, then B = 64 since SHA-1 manipulates 64-byte blocks.
We denote t as the byte-length of the truncation output. For
instance, if t = 6, then the output of the truncation is a 6-byte
value.
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5.1 DataInput Parameters
This structure is the concatenation of all the parameters used in
the computation of the OCRA values, save for the secret key K.
DataInput = {Q | C | P | S | T} where:
. Q is the list of (concatenated) challenge question(s)
generated by the verifier(s);the questions SHOULD be L-byte
values and MUST be at least t-byte values;
. C is a 8-byte counter value processed high-order bit first,
and MUST be synchronized between all parties;
. P is a SHA1-hash of PIN/password that is known to all parties
during the execution of the algorithm;
. S is a string that contains information about the current
session;
. T is a timestamp value, UTC formatted.
When computing a response, the concatenation order is always the
following:
OTHER-PARTY-GENERATED-CHALLENGE-QUESTION
YOUR-GENERATED-CHALLENGE-QUESTION
C, P, S and then T values.
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.
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.
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
dynamic truncation as described in [RFC 4226] to extract a t-byte
value;
- t=0 means that no truncation is performed and the full HMAC value
is used for authentication purpose.
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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-SHA256-6: HOTP with SHA-1 as the hash function for HMAC
and a dynamic truncation to a 6-digit value;
. HOTP-SHA512-6: HOTP with SHA-1 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
The following values define the OcraSuite codes used in the
description of modes of operation for the OCRA algorithm.
An OCRASuite value defines an OCRA suite of operations as supported
in the present draft and is represented as follows:
Algorithm-CryptoFunction-DataInput
Algorithm
---------
Description: Indicates the OCRA algorithm (possibly authenticated)
Values: String MUST contains OCRA and optionally, the OCRA computed
value of the string
CryptoFunction
--------------
Description: Indicated the function used to compute OCRA values
Values: As described in previous section; other values COULD be
added in the future
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DataInput
---------
Description: List of valid inputs for the computation; [] indicates
a value is optional.
Values:
Q | [C | P | S | T]: Challenge-Response computation
C | [P]: Response-only (OTP) computation
Q | [C | P | T]: Plain Signature computation
Example of possible values: OCRA-HOTP-SHA512-8-C-P-Q means OCRA
algorithm with HMAC-SHA512 function, truncated to an 8-digit value,
using the counter, hash of the PIN/Password and a random challenge
as parameter, the other party MUST check the value received before
computing and sending his response.
7. Algorithm Modes for Authentication
In this section we describe the typical modes in which the above
defined computation can be used for authentication.
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:
Q - Challenge question, mandatory, supplied by the verifier.
C - Counter, optional.
P - Hashed version of PIN/password, optional.
S - Session information, optional
T - Timestamp, optional.
The picture below shows the messages that are exchanged between the
client (prover) and the server (verifier) to complete a one-way
challenge-response authentication.
We assume that the client and server have a pre-shared key K that
is used for the computation.
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CLIENT SERVER
(PROVER) (VERIFIER)
| |
| Verifier sends challenge to prover |
| Challenge = Q |
|<------------------------------------------|
| |
| Prover Computes Response |
| R = OCRA(K, {Q| [C | P | S | T]}) |
| Response = R |
|------------------------------------------>|
| |
| Verifier Validates Response |
| Response = OK |
|<------------------------------------------|
| |
7.2. Response Only (OTP) Mode
Response Only mode is a variation of one-way challenge-response
where the challenge is implicitly derived.
In order to implicitly derive the challenge, the verifier and the
prover need to maintain a moving factor that is synchronized.
Commonly used moving factors include a counter, time or combination
of both.
To use this algorithm, the prover will use the implicit challenge
in the computation as described above. The prover then communicates
the response to the verifier to authenticate.
Therefore in this mode, the data inputs will be:
C - Counter mandatory.
P - Hashed version of PIN/password, optional.
The picture below shows the messages that are exchanged between the
client (prover) and the server (verifier) to complete a response
only authentication.
We assume that the client and server have a pre-shared key K that
is used for the computation.
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CLIENT SERVER
(PROVER) (VERIFIER)
| |
| |
| Prover Computes Response |
| R = OCRA(K, C | [P]) |
| Response = R |
|------------------------------------------>|
| |
| Verifier Validates Response |
| Response = OK |
|<------------------------------------------|
| |
7.3. Mutual Challenge-Response
Mutual challenge-response is a variation of one-way challenge-
response where both the client and server and 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 authenticate
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:
Q1 - Challenge question, mandatory, supplied by the client.
Q2 - Challenge question, mandatory, supplied by the server.
C - Counter, optional.
S - Session information, optional.
T - Timestamp, optional.
Typical data inputs for client-response computation will be:
Q2 - Challenge question, mandatory, supplied by the server.
Q1 - Challenge question, mandatory, supplied by the client.
C - Counter, optional.
P - Hashed version of PIN/password, optional.
S - Session information, optional.
T - Timestamp, optional.
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The following picture shows the messages that are exchanged between
the client and the server to complete a two-way mutual challenge-
response authentication.
We assume that the client and server have a pre-shared key K that
is used for the computation.
CLIENT SERVER
| |
| 1. Client sends client-challenge |
| Q1 = Client-challenge |
|------------------------------------------>|
| |
| 2. Server computes server-response |
| and sends server-challenge |
| R1 = OCRA(K, Q1 | Q2 | [C | S | T]) |
| Q2 = Server-challenge |
| Response = R1, Q2 |
|<------------------------------------------|
| |
| 3. Client verifies server-response |
| and computes client-response |
| OCRA(K, Q1, Q2,[C,S,T]) != R1 -> STOP |
| R2 = ORCA( K,Q2 | Q1 | [C | P | S | T])|
| Response = R2 |
|------------------------------------------>|
| |
| 4. Server verifies client-response |
| OCRA(K, Q2|Q1|[C|P|S|T]) != R2 -> 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.
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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:
Q - Signature-challenge, mandatory, supplied by the server.
C - Counter, optional.
P - Hashed version of PIN/password, optional.
T - Timestamp, optional.
The picture below shows the messages that are exchanged between the
client (prover) and the server (verifier) to complete a plain
signature operation.
We assume 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 = Q |
|<------------------------------------------|
| |
| Client Computes Response |
| SIGN = OCRA(K, Q | [C | 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 authenticate that it is talking to a valid server
before creating 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.
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In this mode there are two computations: client-signature and
server-response.
Typical data inputs for server-response computation will be:
Q - Challenge question, mandatory, supplied by the client.
C - Counter, optional.
T - Timestamp, optional.
Typical data inputs for client-signature computation will be:
Q - Signature-challenge, mandatory, supplied by the server.
P - Hashed version of PIN/password, optional.
C - Counter, optional.
T - Timestamp, optional.
The picture below shows the messages that are exchanged between the
client and the server to complete a signature with server
authentication transaction.
We assume that the client and server have a pre-shared key K that
is used for the computation.
CLIENT SERVER
| |
| 1. Client sends client-challenge |
| Q1 = Client-challenge |
|------------------------------------------>|
| |
| 2. Server computes server-response |
| and sends signature-challenge |
| R1 = OCRA(K, Q1 | Q2 | [C | T]) |
| Q2 = signature-challenge |
| Response = R1, Q2 |
|<------------------------------------------|
| |
| 3. Client verifies server-response |
| and computes signature |
| OCRA(K, Q1 | [T | C]) != R1 -> STOP |
| R2 = ORCA( K, Q2 | Q1 | [C | P | T]) |
| Signature = R2 |
|------------------------------------------>|
| |
| 4. Server verifies Signature |
| OCRA(K, Q2|Q1| [C|P|T]) != R2 -> STOP |
| Response = OK |
|<------------------------------------------|
| |
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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.
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
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.
The keys for HOTP can be of any length equal or longer than L
bytes. Keys longer than L bytes are acceptable; they are first
hashed using the supported hash function, e.g. SHA-1, to become
usable. Nevertheless, the extra length would not significantly
increase the cryptographic strength of OCRA, provided the
randomness of the original key material is sufficient.
Keys need to 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].
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The keys MUST be embedded in a tamper resistance 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).
The challenge value MUST be randomly generated for each use of the
authentication protocol and SHALL NOT be re-used. We RECOMMEND
following the recommendations in [RFC1750] for all pseudo-random
and random generations.
All the communications SHOULD take place over a secure channel e.g.
SSL/TLS, IPsec connections.
The OCRA algorithm when used in mutual authentication mode or in
signature with server authentication mode SHOULD 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 the same on the server side.
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.
10. IANA Considerations
This document has no actions for IANA.
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 cross-authentication both in connected
and off-line modes, with the support of different response sizes
and mode of operations.
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12. Acknowledgements
We would like to thank Philip Hoyer, Jon Martinsson, Frederik
Mennes and Stu Vaeth 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
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
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Appendix A: Code Source
import java.lang.reflect.UndeclaredThrowableException;
import java.security.GeneralSecurityException;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
/**
* 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);
} 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
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OCRA: OATH Challenge Response Algorithms September 2006
* set of parameters.
*
* @param crypto the crypto algorithm
* @param key the shared secret
* @param movingFactor the counter that changes
* on a per use basis
* @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
* @param codeDigits number of digits in the OTP
*
* @return A numeric String in base 10 that includes
* {@link truncationDigits} digits
*/
static public String generateOTP(String crypto,
String key,
String movingFactor,
String question,
String password,
String sessionInformation,
String timeStamp,
int codeDigits)
{
String result = null;
String messageStr =
question + password +
sessionInformation + timeStamp ;
byte[] msg;
// Using the counter
if (0 < movingFactor.length()){
// First 8 bytes are for the movingFactor
// Complient with RFC 4226
messageStr = "00000000" + messageStr;
msg = messageStr.getBytes();
long mFactor = Long.decode(movingFactor);
for (int i = 7; i >= 0; i--) {
msg[i] = (byte) (mFactor & 0xff);
mFactor >>= 8;
}
}else
msg = messageStr.getBytes();
// compute hmac hash
byte[] hash = hmac_sha1(crypto, key.getBytes(), msg);
// put selected bytes into result int
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OCRA: OATH Challenge Response Algorithms September 2006
int offset = hash[hash.length - 1] & 0xf;
int binary =
((hash[offset] & 0x7f) << 24) |
((hash[offset + 1] & 0xff) << 16) |
((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
Plain challenge response
========================
OCRA-HOTP-SHA1-8-Q
------------------
K = 12345678901234567890 Q = 10000000 OCRA = 57953866
K = 12345678901234567890 Q = 10000001 OCRA = 15772773
K = 12345678901234567890 Q = 10000002 OCRA = 68105940
OCRA-HOTP-SHA256-8-Q
--------------------
K = 12345678901234567890 Q = 10000000 OCRA = 79730854
K = 12345678901234567890 Q = 10000001 OCRA = 22925447
K = 12345678901234567890 Q = 10000002 OCRA = 15947867
OCRA-HOTP-SHA512-8-Q
--------------------
K = 12345678901234567890 Q = 10000000 OCRA = 68325835
K = 12345678901234567890 Q = 10000001 OCRA = 53995836
K = 12345678901234567890 Q = 10000002 OCRA = 89008345
Response Only
=============
OCRA-HOTP-SHA1-6-C
------------------
K = 12345678901234567890 C = 0 OCRA = 755224
K = 12345678901234567890 C = 1 OCRA = 287082
K = 12345678901234567890 C = 2 OCRA = 359152
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OCRA: OATH Challenge Response Algorithms September 2006
OCRA-HOTP-SHA256-6-C
--------------------
K = 12345678901234567890 C = 0 OCRA = 875740
K = 12345678901234567890 C = 1 OCRA = 247374
K = 12345678901234567890 C = 2 OCRA = 254785
OCRA-HOTP-SHA512-6-C
--------------------
K = 12345678901234567890 C = 0 OCRA = 125165
K = 12345678901234567890 C = 1 OCRA = 342147
K = 12345678901234567890 C = 2 OCRA = 730102
OCRA-HOTP-SHA1-6-C-P
--------------------
K = 12345678901234567890 C = 0 P = 12341234 OCRA = 106753
K = 12345678901234567890 C = 1 P = 12341234 OCRA = 747071
K = 12345678901234567890 C = 2 P = 12341234 OCRA = 714367
OCRA-HOTP-SHA256-6-C-P
----------------------
K = 12345678901234567890 C = 0 P = 12341234 OCRA = 744059
K = 12345678901234567890 C = 1 P = 12341234 OCRA = 735947
K = 12345678901234567890 C = 2 P = 12341234 OCRA = 167188
OCRA-HOTP-SHA512-6-C-P
----------------------
K = 12345678901234567890 C = 0 P = 12341234 OCRA = 249058
K = 12345678901234567890 C = 1 P = 12341234 OCRA = 738728
K = 12345678901234567890 C = 2 P = 12341234 OCRA = 556127
Mutual challenge response
=========================
OCRA-HOTP-SHA512-8-Q
--------------------
(From server) K = 12345678901234567890
Q1 = 11111110 Q2 = 22222220 OCRA = 70933163
(From client) K = 12345678901234567890
Q1 = 11111110 Q2 = 22222220 OCRA = 63875222
(From server) K = 12345678901234567890
Q1 = 11111111 Q2 = 22222221 OCRA = 08364053
(From client) K = 12345678901234567890
Q1 = 11111111 Q2 = 22222221 OCRA = 91844292
(From server) K = 12345678901234567890
Q1 = 11111112 Q2 = 22222222 OCRA = 70960179
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OCRA: OATH Challenge Response Algorithms September 2006
(From client) K = 12345678901234567890
Q1 = 11111112 Q2 = 22222222 OCRA = 75789938
Plain signature
===============
OCRA-HOTP-SHA512-8-Q
--------------------
K = 12345678901234567890 Q (value) = 00010000
OCRA (signature) = 13175449
K = 12345678901234567890 Q (value) = 00011000
OCRA (signature) = 41866883
K = 12345678901234567890 Q (value) = 00012000
OCRA (signature) = 82912137
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.
624 Ellis Street, Suite 102 Phone: 1-650-515-3569
Mountain View, CA 94043 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
OATH-HOTP-VARIANTS Expires - March 2007 [Page 21]
OCRA: OATH Challenge Response Algorithms September 2006
15. Full Copyright Statement
Copyright (C) The IETF Trust (2006).
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.
This document and the information contained herein are provided on
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OATH-HOTP-VARIANTS Expires - March 2007 [Page 22]