1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
|
package org.spongycastle.crypto.agreement.srp;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.spongycastle.crypto.CryptoException;
import org.spongycastle.crypto.Digest;
/**
* 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 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;
}
/**
* 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 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 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);
}
}
|
