Examples with DSAPrivateKeyParameters org.spongycastle.crypto.params.DSAPrivateKeyParameters used on opensource projects

Example 1 with DSAPrivateKeyParameters

use of org.spongycastle.crypto.params.DSAPrivateKeyParameters in project Zom-Android by zom.

the class OtrCryptoEngineImpl method sign.

public byte[] sign(byte[] b, PrivateKey privatekey) throws OtrCryptoException {
    if (!(privatekey instanceof DSAPrivateKey))
        throw new IllegalArgumentException();
    DSAParams dsaParams = ((DSAPrivateKey) privatekey).getParams();
    DSAParameters bcDSAParameters = new DSAParameters(dsaParams.getP(), dsaParams.getQ(), dsaParams.getG());
    DSAPrivateKey dsaPrivateKey = (DSAPrivateKey) privatekey;
    DSAPrivateKeyParameters bcDSAPrivateKeyParms = new DSAPrivateKeyParameters(dsaPrivateKey.getX(), bcDSAParameters);
    DSASigner dsaSigner = new DSASigner();
    dsaSigner.init(true, bcDSAPrivateKeyParms);
    BigInteger q = dsaParams.getQ();
    // Ian: Note that if you can get the standard DSA implementation you're
    // using to not hash its input, you should be able to pass it ((256-bit
    // value) mod q), (rather than truncating the 256-bit value) and all
    // should be well.
    // ref: Interop problems with libotr - DSA signature
    BigInteger bmpi = new BigInteger(1, b);
    BigInteger[] rs = dsaSigner.generateSignature(BigIntegers.asUnsignedByteArray(bmpi.mod(q)));
    int siglen = q.bitLength() / 4;
    int rslen = siglen / 2;
    byte[] rb = BigIntegers.asUnsignedByteArray(rs[0]);
    byte[] sb = BigIntegers.asUnsignedByteArray(rs[1]);
    // Create the final signature array, padded with zeros if necessary.
    byte[] sig = new byte[siglen];
    Boolean writeR = false;
    Boolean writeS = false;
    int shiftR = rslen - rb.length;
    int shiftS = rslen - sb.length;
    for (int i = 0; i < siglen; i++) {
        if (i < rslen) {
            if (!writeR)
                writeR = rb.length >= rslen - i;
            sig[i] = (writeR) ? rb[i - shiftR] : (byte) 0x0;
        } else {
            // Rebase.
            int j = i - rslen;
            if (!writeS)
                writeS = sb.length >= rslen - j;
            sig[i] = (writeS) ? sb[j - shiftS] : (byte) 0x0;
        }
    }
    return sig;
}