13ff48bf5SDavid du Colombier #include "os.h"
23ff48bf5SDavid du Colombier #include <mp.h>
33ff48bf5SDavid du Colombier #include <libsec.h>
43ff48bf5SDavid du Colombier
53ff48bf5SDavid du Colombier int
dsaverify(DSApub * pub,DSAsig * sig,mpint * m)63ff48bf5SDavid du Colombier dsaverify(DSApub *pub, DSAsig *sig, mpint *m)
73ff48bf5SDavid du Colombier {
83ff48bf5SDavid du Colombier int rv = -1;
93ff48bf5SDavid du Colombier mpint *u1, *u2, *v, *sinv;
103ff48bf5SDavid du Colombier
11*39734e7eSDavid du Colombier if(mpcmp(sig->r, mpone) < 0 || mpcmp(sig->r, pub->q) >= 0)
123ff48bf5SDavid du Colombier return rv;
13*39734e7eSDavid du Colombier if(mpcmp(sig->s, mpone) < 0 || mpcmp(sig->s, pub->q) >= 0)
143ff48bf5SDavid du Colombier return rv;
153ff48bf5SDavid du Colombier u1 = mpnew(0);
163ff48bf5SDavid du Colombier u2 = mpnew(0);
173ff48bf5SDavid du Colombier v = mpnew(0);
183ff48bf5SDavid du Colombier sinv = mpnew(0);
193ff48bf5SDavid du Colombier
203ff48bf5SDavid du Colombier // find (s**-1) mod q, make sure it exists
213ff48bf5SDavid du Colombier mpextendedgcd(sig->s, pub->q, u1, sinv, v);
223ff48bf5SDavid du Colombier if(mpcmp(u1, mpone) != 0)
233ff48bf5SDavid du Colombier goto out;
243ff48bf5SDavid du Colombier
253ff48bf5SDavid du Colombier // u1 = (sinv * m) mod q, u2 = (r * sinv) mod q
263ff48bf5SDavid du Colombier mpmul(sinv, m, u1);
273ff48bf5SDavid du Colombier mpmod(u1, pub->q, u1);
283ff48bf5SDavid du Colombier mpmul(sig->r, sinv, u2);
293ff48bf5SDavid du Colombier mpmod(u2, pub->q, u2);
303ff48bf5SDavid du Colombier
313ff48bf5SDavid du Colombier // v = (((alpha**u1)*(key**u2)) mod p) mod q
323ff48bf5SDavid du Colombier mpexp(pub->alpha, u1, pub->p, sinv);
333ff48bf5SDavid du Colombier mpexp(pub->key, u2, pub->p, v);
343ff48bf5SDavid du Colombier mpmul(sinv, v, v);
353ff48bf5SDavid du Colombier mpmod(v, pub->p, v);
363ff48bf5SDavid du Colombier mpmod(v, pub->q, v);
373ff48bf5SDavid du Colombier
383ff48bf5SDavid du Colombier if(mpcmp(v, sig->r) == 0)
393ff48bf5SDavid du Colombier rv = 0;
403ff48bf5SDavid du Colombier out:
413ff48bf5SDavid du Colombier mpfree(v);
423ff48bf5SDavid du Colombier mpfree(u1);
433ff48bf5SDavid du Colombier mpfree(u2);
443ff48bf5SDavid du Colombier mpfree(sinv);
453ff48bf5SDavid du Colombier return rv;
463ff48bf5SDavid du Colombier }
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