einf.java

einf.java

package com.tsusanka.dsa;

import java.math.BigInteger;

class DSA
{

    private BigInteger alpha;
    private BigInteger beta;
    private BigInteger p;
    private BigInteger q;

    DSA(BigInteger alpha, BigInteger beta, BigInteger p, BigInteger q)
    {
        this.alpha = alpha;
        this.beta = beta;
        this.p = p;
        this.q = q;
    }

    Signature sign(BigInteger key, BigInteger ephemeral, BigInteger hash)
    {
        BigInteger r, s;
        r = alpha.modPow(ephemeral, p).mod(q);
        s = (hash.add(key.multiply(r))).mod(q).multiply(ephemeral.modInverse(q)).mod(q);
        return new Signature(r, s);
    }

    boolean verify(Signature signature, BigInteger hash)
    {
        BigInteger w, u1, u2, v;
        w = signature.s.modInverse(q);
        u1 = w.multiply(hash).mod(q);
        u2 = w.multiply(signature.r).mod(q);
        v = (alpha.modPow(u1, p).multiply(beta.modPow(u2, p))).mod(p).mod(q);

        return v.equals(signature.r);
    }

}