org.spongycastle.crypto.agreement.jpake

Class JPAKEUtil

java.lang.Object

org.spongycastle.crypto.agreement.jpake.JPAKEUtil

public class JPAKEUtil
extends java.lang.Object

Primitives needed for a J-PAKE exchange.

The recommended way to perform a J-PAKE exchange is by using two JPAKEParticipants. Internally, those participants call these primitive operations in JPAKEUtil.

The primitives, however, can be used without a JPAKEParticipant if needed.

Constructor Summary

Constructors

Constructor and Description
JPAKEUtil()

Method Summary

Modifier and Type	Method and Description
static java.math.BigInteger	calculateA(java.math.BigInteger p, java.math.BigInteger q, java.math.BigInteger gA, java.math.BigInteger x2s) Calculate A as done in round 2.
static java.math.BigInteger	calculateGA(java.math.BigInteger p, java.math.BigInteger gx1, java.math.BigInteger gx3, java.math.BigInteger gx4) Calculate ga as done in round 2.
static java.math.BigInteger	calculateGx(java.math.BigInteger p, java.math.BigInteger g, java.math.BigInteger x) Calculate g^x mod p as done in round 1.
static java.math.BigInteger	calculateKeyingMaterial(java.math.BigInteger p, java.math.BigInteger q, java.math.BigInteger gx4, java.math.BigInteger x2, java.math.BigInteger s, java.math.BigInteger B) Calculates the keying material, which can be done after round 2 has completed.
static java.math.BigInteger	calculateMacTag(java.lang.String participantId, java.lang.String partnerParticipantId, java.math.BigInteger gx1, java.math.BigInteger gx2, java.math.BigInteger gx3, java.math.BigInteger gx4, java.math.BigInteger keyingMaterial, Digest digest) Calculates the MacTag (to be used for key confirmation), as defined by NIST SP 800-56A Revision 1, Section 8.2 Unilateral Key Confirmation for Key Agreement Schemes.
static java.math.BigInteger	calculateS(char[] password) Converts the given password to a BigInteger for use in arithmetic calculations.
static java.math.BigInteger	calculateX2s(java.math.BigInteger q, java.math.BigInteger x2, java.math.BigInteger s) Calculate x2 * s as done in round 2.
static java.math.BigInteger[]	calculateZeroKnowledgeProof(java.math.BigInteger p, java.math.BigInteger q, java.math.BigInteger g, java.math.BigInteger gx, java.math.BigInteger x, java.lang.String participantId, Digest digest, java.security.SecureRandom random) Calculate a zero knowledge proof of x using Schnorr's signature.
static java.math.BigInteger	generateX1(java.math.BigInteger q, java.security.SecureRandom random) Return a value that can be used as x1 or x3 during round 1.
static java.math.BigInteger	generateX2(java.math.BigInteger q, java.security.SecureRandom random) Return a value that can be used as x2 or x4 during round 1.
static void	validateGa(java.math.BigInteger ga) Validates that ga is not 1.
static void	validateGx4(java.math.BigInteger gx4) Validates that g^x4 is not 1.
static void	validateMacTag(java.lang.String participantId, java.lang.String partnerParticipantId, java.math.BigInteger gx1, java.math.BigInteger gx2, java.math.BigInteger gx3, java.math.BigInteger gx4, java.math.BigInteger keyingMaterial, Digest digest, java.math.BigInteger partnerMacTag) Validates the MacTag received from the partner participant.
static void	validateNotNull(java.lang.Object object, java.lang.String description) Validates that the given object is not null.
static void	validateParticipantIdsDiffer(java.lang.String participantId1, java.lang.String participantId2) Validates that the given participant ids are not equal.
static void	validateParticipantIdsEqual(java.lang.String expectedParticipantId, java.lang.String actualParticipantId) Validates that the given participant ids are equal.
static void	validateZeroKnowledgeProof(java.math.BigInteger p, java.math.BigInteger q, java.math.BigInteger g, java.math.BigInteger gx, java.math.BigInteger[] zeroKnowledgeProof, java.lang.String participantId, Digest digest) Validates the zero knowledge proof (generated by calculateZeroKnowledgeProof(BigInteger, BigInteger, BigInteger, BigInteger, BigInteger, String, Digest, SecureRandom)) is correct.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

JPAKEUtil

public JPAKEUtil()

Method Detail

generateX1

public static java.math.BigInteger generateX1(java.math.BigInteger q,
                                              java.security.SecureRandom random)

Return a value that can be used as x1 or x3 during round 1.

The returned value is a random value in the range [0, q-1].

generateX2

public static java.math.BigInteger generateX2(java.math.BigInteger q,
                                              java.security.SecureRandom random)

Return a value that can be used as x2 or x4 during round 1.

The returned value is a random value in the range [1, q-1].

calculateS

public static java.math.BigInteger calculateS(char[] password)

Converts the given password to a BigInteger for use in arithmetic calculations.

calculateGx

public static java.math.BigInteger calculateGx(java.math.BigInteger p,
                                               java.math.BigInteger g,
                                               java.math.BigInteger x)

Calculate g^x mod p as done in round 1.

calculateGA

public static java.math.BigInteger calculateGA(java.math.BigInteger p,
                                               java.math.BigInteger gx1,
                                               java.math.BigInteger gx3,
                                               java.math.BigInteger gx4)

Calculate ga as done in round 2.

calculateX2s

public static java.math.BigInteger calculateX2s(java.math.BigInteger q,
                                                java.math.BigInteger x2,
                                                java.math.BigInteger s)

Calculate x2 * s as done in round 2.

calculateA

public static java.math.BigInteger calculateA(java.math.BigInteger p,
                                              java.math.BigInteger q,
                                              java.math.BigInteger gA,
                                              java.math.BigInteger x2s)

Calculate A as done in round 2.

calculateZeroKnowledgeProof

public static java.math.BigInteger[] calculateZeroKnowledgeProof(java.math.BigInteger p,
                                                                 java.math.BigInteger q,
                                                                 java.math.BigInteger g,
                                                                 java.math.BigInteger gx,
                                                                 java.math.BigInteger x,
                                                                 java.lang.String participantId,
                                                                 Digest digest,
                                                                 java.security.SecureRandom random)

Calculate a zero knowledge proof of x using Schnorr's signature. The returned array has two elements {g^v, r = v-x*h} for x.

validateGx4

public static void validateGx4(java.math.BigInteger gx4)
                        throws CryptoException

Validates that g^x4 is not 1.

Throws:

CryptoException - if g^x4 is 1

validateGa

public static void validateGa(java.math.BigInteger ga)
                       throws CryptoException

Validates that ga is not 1.

As described by Feng Hao...

Alice could simply check ga != 1 to ensure it is a generator. In fact, as we will explain in Section 3, (x1 + x3 + x4 ) is random over Zq even in the face of active attacks. Hence, the probability for ga = 1 is extremely small - on the order of 2^160 for 160-bit q.

Throws:

CryptoException - if ga is 1

validateZeroKnowledgeProof

public static void validateZeroKnowledgeProof(java.math.BigInteger p,
                                              java.math.BigInteger q,
                                              java.math.BigInteger g,
                                              java.math.BigInteger gx,
                                              java.math.BigInteger[] zeroKnowledgeProof,
                                              java.lang.String participantId,
                                              Digest digest)
                                       throws CryptoException

Validates the zero knowledge proof (generated by calculateZeroKnowledgeProof(BigInteger, BigInteger, BigInteger, BigInteger, BigInteger, String, Digest, SecureRandom)) is correct.

Throws:

CryptoException - if the zero knowledge proof is not correct

calculateKeyingMaterial

public static java.math.BigInteger calculateKeyingMaterial(java.math.BigInteger p,
                                                           java.math.BigInteger q,
                                                           java.math.BigInteger gx4,
                                                           java.math.BigInteger x2,
                                                           java.math.BigInteger s,
                                                           java.math.BigInteger B)

Calculates the keying material, which can be done after round 2 has completed. A session key must be derived from this key material using a secure key derivation function (KDF). The KDF used to derive the key is handled externally (i.e. not by JPAKEParticipant).

 KeyingMaterial = (B/g^{x2*x4*s})^x2
 

validateParticipantIdsDiffer

public static void validateParticipantIdsDiffer(java.lang.String participantId1,
                                                java.lang.String participantId2)
                                         throws CryptoException

Validates that the given participant ids are not equal. (For the J-PAKE exchange, each participant must use a unique id.)

Throws:

CryptoException - if the participantId strings are equal.

validateParticipantIdsEqual

public static void validateParticipantIdsEqual(java.lang.String expectedParticipantId,
                                               java.lang.String actualParticipantId)
                                        throws CryptoException

Validates that the given participant ids are equal. This is used to ensure that the payloads received from each round all come from the same participant.

Throws:

CryptoException - if the participantId strings are equal.

validateNotNull

public static void validateNotNull(java.lang.Object object,
                                   java.lang.String description)

Validates that the given object is not null.

Parameters:

object - object in question

description - name of the object (to be used in exception message)

Throws:

java.lang.NullPointerException - if the object is null.

calculateMacTag

public static java.math.BigInteger calculateMacTag(java.lang.String participantId,
                                                   java.lang.String partnerParticipantId,
                                                   java.math.BigInteger gx1,
                                                   java.math.BigInteger gx2,
                                                   java.math.BigInteger gx3,
                                                   java.math.BigInteger gx4,
                                                   java.math.BigInteger keyingMaterial,
                                                   Digest digest)

Calculates the MacTag (to be used for key confirmation), as defined by NIST SP 800-56A Revision 1, Section 8.2 Unilateral Key Confirmation for Key Agreement Schemes.

 MacTag = HMAC(MacKey, MacLen, MacData)

 MacKey = H(K || "JPAKE_KC")

 MacData = "KC_1_U" || participantId || partnerParticipantId || gx1 || gx2 || gx3 || gx4

 Note that both participants use "KC_1_U" because the sender of the round 3 message
 is always the initiator for key confirmation.

 HMAC = HMac used with the given Digest
 H = The given Digest
 MacLen = length of MacTag
 

validateMacTag

public static void validateMacTag(java.lang.String participantId,
                                  java.lang.String partnerParticipantId,
                                  java.math.BigInteger gx1,
                                  java.math.BigInteger gx2,
                                  java.math.BigInteger gx3,
                                  java.math.BigInteger gx4,
                                  java.math.BigInteger keyingMaterial,
                                  Digest digest,
                                  java.math.BigInteger partnerMacTag)
                           throws CryptoException

Validates the MacTag received from the partner participant.

Parameters:

partnerMacTag - the MacTag received from the partner.

Throws:

CryptoException - if the participantId strings are equal.