ref: 0e516cbf488a9ec8edae3dc6efca2baa0c3d95bd
dir: /sys/src/libsec/port/dsaverify.c/
#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; }