private OutgoingMessage sendParameters(final IncomingMessage in) throws KeyAgreementException {
final String I = in.readString();
// get s and v for user identified by I
// ----------------------------------------------------------------------
final Map credentials;
try {
final Map userID = new HashMap();
userID.put(Registry.SASL_USERNAME, I);
userID.put(SRPRegistry.MD_NAME_FIELD, srp.getAlgorithm());
credentials = passwordDB.lookup(userID);
} catch (IOException x) {
throw new KeyAgreementException("computeSharedSecret()", x);
}
final BigInteger s =
new BigInteger(1, Util.fromBase64((String) credentials.get(SRPRegistry.SALT_FIELD)));
final BigInteger v =
new BigInteger(
1, Util.fromBase64((String) credentials.get(SRPRegistry.USER_VERIFIER_FIELD)));
final Map configuration;
try {
final String mode = (String) credentials.get(SRPRegistry.CONFIG_NDX_FIELD);
configuration = passwordDB.getConfiguration(mode);
} catch (IOException x) {
throw new KeyAgreementException("computeSharedSecret()", x);
}
N = new BigInteger(1, Util.fromBase64((String) configuration.get(SRPRegistry.SHARED_MODULUS)));
g = new BigInteger(1, Util.fromBase64((String) configuration.get(SRPRegistry.FIELD_GENERATOR)));
// ----------------------------------------------------------------------
// generate an ephemeral keypair
final SRPKeyPairGenerator kpg = new SRPKeyPairGenerator();
final Map attributes = new HashMap();
if (rnd != null) {
attributes.put(SRPKeyPairGenerator.SOURCE_OF_RANDOMNESS, rnd);
}
attributes.put(SRPKeyPairGenerator.SHARED_MODULUS, N);
attributes.put(SRPKeyPairGenerator.GENERATOR, g);
attributes.put(SRPKeyPairGenerator.USER_VERIFIER, v);
kpg.setup(attributes);
hostKeyPair = kpg.generate();
final BigInteger B = ((SRPPublicKey) hostKeyPair.getPublic()).getY();
final OutgoingMessage result = new OutgoingMessage();
result.writeMPI(N);
result.writeMPI(g);
result.writeMPI(s);
result.writeMPI(B);
return result;
}
protected OutgoingMessage computeSharedSecret(final IncomingMessage in)
throws KeyAgreementException {
N = in.readMPI();
g = in.readMPI();
final BigInteger s = in.readMPI();
final BigInteger B = in.readMPI();
if (B.mod(N).equals(BigInteger.ZERO)) {
throw new KeyAgreementException("illegal value for B");
}
// generate an ephemeral keypair
final SRPKeyPairGenerator kpg = new SRPKeyPairGenerator();
final Map attributes = new HashMap();
if (rnd != null) {
attributes.put(SRPKeyPairGenerator.SOURCE_OF_RANDOMNESS, rnd);
}
attributes.put(SRPKeyPairGenerator.SHARED_MODULUS, N);
attributes.put(SRPKeyPairGenerator.GENERATOR, g);
kpg.setup(attributes);
userKeyPair = kpg.generate();
final BigInteger A = ((SRPPublicKey) userKeyPair.getPublic()).getY();
final BigInteger u = uValue(A, B); // u = H(A | B)
if (u.mod(N).equals(BigInteger.ZERO)) {
throw new KeyAgreementException("u is zero");
}
final BigInteger x;
try {
x = new BigInteger(1, srp.computeX(Util.trim(s), I, p));
} catch (Exception e) {
throw new KeyAgreementException("computeSharedSecret()", e);
}
// compute S = (B - 3g^x) ^ (a + ux)
final BigInteger a = ((SRPPrivateKey) userKeyPair.getPrivate()).getX();
final BigInteger S = B.subtract(THREE.multiply(g.modPow(x, N))).modPow(a.add(u.multiply(x)), N);
K = S;
final OutgoingMessage result = new OutgoingMessage();
result.writeMPI(A);
complete = true;
return result;
}
