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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8 with debug enabled.
package org.bouncycastle.crypto.agreement.srp;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.bouncycastle.crypto.CryptoException;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.params.SRP6GroupParameters;
/**
* Implements the client side SRP-6a protocol. Note that this class is stateful, and therefore NOT threadsafe.
* This implementation of SRP is based on the optimized message sequence put forth by Thomas Wu in the paper
* "SRP-6: Improvements and Refinements to the Secure Remote Password Protocol, 2002"
*/
public class SRP6Client
{
protected BigInteger N;
protected BigInteger g;
protected BigInteger a;
protected BigInteger A;
protected BigInteger B;
protected BigInteger x;
protected BigInteger u;
protected BigInteger S;
protected BigInteger M1;
protected BigInteger M2;
protected BigInteger Key;
protected Digest digest;
protected SecureRandom random;
public SRP6Client()
{
}
/**
* Initialises the client to begin new authentication attempt
* @param N The safe prime associated with the client's verifier
* @param g The group parameter associated with the client's verifier
* @param digest The digest algorithm associated with the client's verifier
* @param random For key generation
*/
public void init(BigInteger N, BigInteger g, Digest digest, SecureRandom random)
{
this.N = N;
this.g = g;
this.digest = digest;
this.random = random;
}
public void init(SRP6GroupParameters group, Digest digest, SecureRandom random)
{
init(group.getN(), group.getG(), digest, random);
}
/**
* Generates client's credentials given the client's salt, identity and password
* @param salt The salt used in the client's verifier.
* @param identity The user's identity (eg. username)
* @param password The user's password
* @return Client's public value to send to server
*/
public BigInteger generateClientCredentials(byte[] salt, byte[] identity, byte[] password)
{
this.x = SRP6Util.calculateX(digest, N, salt, identity, password);
this.a = selectPrivateValue();
this.A = g.modPow(a, N);
return A;
}
/**
* Generates the secret S given the server's credentials
* @param serverB The server's credentials
* @return Client's verification message for the server
* @throws CryptoException If server's credentials are invalid
*/
public BigInteger calculateSecret(BigInteger serverB) throws CryptoException
{
this.B = SRP6Util.validatePublicValue(N, serverB);
this.u = SRP6Util.calculateU(digest, N, A, B);
this.S = calculateS();
return S;
}
protected BigInteger selectPrivateValue()
{
return SRP6Util.generatePrivateValue(digest, N, g, random);
}
private BigInteger calculateS()
{
BigInteger k = SRP6Util.calculateK(digest, N, g);
BigInteger exp = u.multiply(x).add(a);
BigInteger tmp = g.modPow(x, N).multiply(k).mod(N);
return B.subtract(tmp).mod(N).modPow(exp, N);
}
/**
* Computes the client evidence message M1 using the previously received values.
* To be called after calculating the secret S.
* @return M1: the client side generated evidence message
* @throws CryptoException
*/
public BigInteger calculateClientEvidenceMessage() throws CryptoException
{
// Verify pre-requirements
if (this.A == null || this.B == null || this.S == null)
{
throw new CryptoException("Impossible to compute M1: " +
"some data are missing from the previous operations (A,B,S)");
}
// compute the client evidence message 'M1'
this.M1 = SRP6Util.calculateM1(digest, N, A, B, S);
return M1;
}
/** Authenticates the server evidence message M2 received and saves it only if correct.
* @param serverM2 the server side generated evidence message
* @return A boolean indicating if the server message M2 was the expected one.
* @throws CryptoException
*/
public boolean verifyServerEvidenceMessage(BigInteger serverM2) throws CryptoException
{
// Verify pre-requirements
if (this.A == null || this.M1 == null || this.S == null)
{
throw new CryptoException("Impossible to compute and verify M2: " +
"some data are missing from the previous operations (A,M1,S)");
}
// Compute the own server evidence message 'M2'
BigInteger computedM2 = SRP6Util.calculateM2(digest, N, A, M1, S);
if (computedM2.equals(serverM2))
{
this.M2 = serverM2;
return true;
}
return false;
}
/**
* Computes the final session key as a result of the SRP successful mutual authentication
* To be called after verifying the server evidence message M2.
* @return Key: the mutually authenticated symmetric session key
* @throws CryptoException
*/
public BigInteger calculateSessionKey() throws CryptoException
{
// Verify pre-requirements (here we enforce a previous calculation of M1 and M2)
if (this.S == null || this.M1 == null || this.M2 == null)
{
throw new CryptoException("Impossible to compute Key: " +
"some data are missing from the previous operations (S,M1,M2)");
}
this.Key = SRP6Util.calculateKey(digest, N, S);
return Key;
}
}
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