Subversion Repositories planix.SVN

#include "os.h"
#include <mp.h>
#include <libsec.h>

int
dsaverify(DSApub *pub, DSAsig *sig, mpint *m)
{
        int rv = -1;
        mpint *u1, *u2, *v, *sinv;

        if(mpcmp(sig->r, mpone) < 0 || mpcmp(sig->r, pub->q) >= 0)
                return rv;
        if(mpcmp(sig->s, mpone) < 0 || mpcmp(sig->s, pub->q) >= 0)
                return rv;
        u1 = mpnew(0);
        u2 = mpnew(0);
        v = mpnew(0);
        sinv = mpnew(0);

        // find (s**-1) mod q, make sure it exists
        mpextendedgcd(sig->s, pub->q, u1, sinv, v);
        if(mpcmp(u1, mpone) != 0)
                goto out;

        // u1 = (sinv * m) mod q, u2 = (r * sinv) mod q
        mpmul(sinv, m, u1);
        mpmod(u1, pub->q, u1);
        mpmul(sig->r, sinv, u2);
        mpmod(u2, pub->q, u2);

        // v = (((alpha**u1)*(key**u2)) mod p) mod q
        mpexp(pub->alpha, u1, pub->p, sinv);
        mpexp(pub->key, u2, pub->p, v);
        mpmul(sinv, v, v);
        mpmod(v, pub->p, v);
        mpmod(v, pub->q, v);

        if(mpcmp(v, sig->r) == 0)
                rv = 0;
out:
        mpfree(v);
        mpfree(u1);
        mpfree(u2);
        mpfree(sinv);
        return rv;
}