1 files changed, 93 insertions, 0 deletions
diff --git a/crypto/src/crypto/agreement/srp/SRP6Client.cs b/crypto/src/crypto/agreement/srp/SRP6Client.cs
new file mode 100644
index 000000000..309736564
--- /dev/null
+++ b/crypto/src/crypto/agreement/srp/SRP6Client.cs
@@ -0,0 +1,93 @@
+using System;
+
+using Org.BouncyCastle.Math;
+using Org.BouncyCastle.Security;
+
+namespace Org.BouncyCastle.Crypto.Agreement.Srp
+{
+	/**
+	 * 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 privA;
+	    protected BigInteger pubA;
+
+	    protected BigInteger B;
+
+	    protected BigInteger x;
+	    protected BigInteger u;
+	    protected BigInteger S;
+
+	    protected IDigest 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 virtual void Init(BigInteger N, BigInteger g, IDigest digest, SecureRandom random)
+	    {
+	        this.N = N;
+	        this.g = g;
+	        this.digest = digest;
+	        this.random = 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 virtual BigInteger GenerateClientCredentials(byte[] salt, byte[] identity, byte[] password)
+	    {
+	        this.x = Srp6Utilities.CalculateX(digest, N, salt, identity, password);
+	        this.privA = SelectPrivateValue();
+	        this.pubA = g.ModPow(privA, N);
+
+	        return pubA;
+	    }
+
+	    /**
+	     * Generates client's verification message 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 virtual BigInteger CalculateSecret(BigInteger serverB)
+	    {
+	        this.B = Srp6Utilities.ValidatePublicValue(N, serverB);
+	        this.u = Srp6Utilities.CalculateU(digest, N, pubA, B);
+	        this.S = CalculateS();
+
+	        return S;
+	    }
+
+	    protected virtual BigInteger SelectPrivateValue()
+	    {
+	    	return Srp6Utilities.GeneratePrivateValue(digest, N, g, random);    	
+	    }
+
+	    private BigInteger CalculateS()
+	    {
+	        BigInteger k = Srp6Utilities.CalculateK(digest, N, g);
+	        BigInteger exp = u.Multiply(x).Add(privA);
+	        BigInteger tmp = g.ModPow(x, N).Multiply(k).Mod(N);
+	        return B.Subtract(tmp).Mod(N).ModPow(exp, N);
+	    }
+	}
+}