13ff48bf5SDavid du Colombier #include "os.h"
23ff48bf5SDavid du Colombier #include <mp.h>
33ff48bf5SDavid du Colombier #include <libsec.h>
43ff48bf5SDavid du Colombier
53ff48bf5SDavid du Colombier DSAsig*
dsasign(DSApriv * priv,mpint * m)63ff48bf5SDavid du Colombier dsasign(DSApriv *priv, mpint *m)
73ff48bf5SDavid du Colombier {
83ff48bf5SDavid du Colombier DSApub *pub = &priv->pub;
93ff48bf5SDavid du Colombier DSAsig *sig;
103ff48bf5SDavid du Colombier mpint *qm1, *k, *kinv, *r, *s;
113ff48bf5SDavid du Colombier mpint *q = pub->q, *p = pub->p, *alpha = pub->alpha;
123ff48bf5SDavid du Colombier int qlen = mpsignif(q);
133ff48bf5SDavid du Colombier
143ff48bf5SDavid du Colombier qm1 = mpnew(0);
153ff48bf5SDavid du Colombier kinv = mpnew(0);
163ff48bf5SDavid du Colombier r = mpnew(0);
173ff48bf5SDavid du Colombier s = mpnew(0);
183ff48bf5SDavid du Colombier k = mpnew(0);
193ff48bf5SDavid du Colombier mpsub(pub->q, mpone, qm1);
203ff48bf5SDavid du Colombier
213ff48bf5SDavid du Colombier // find a k that has an inverse mod q
223ff48bf5SDavid du Colombier while(1){
233ff48bf5SDavid du Colombier mprand(qlen, genrandom, k);
24*39734e7eSDavid du Colombier if((mpcmp(mpone, k) > 0) || (mpcmp(k, pub->q) >= 0))
253ff48bf5SDavid du Colombier continue;
263ff48bf5SDavid du Colombier mpextendedgcd(k, q, r, kinv, s);
273ff48bf5SDavid du Colombier if(mpcmp(r, mpone) != 0)
28*39734e7eSDavid du Colombier sysfatal("dsasign: pub->q not prime");
293ff48bf5SDavid du Colombier break;
303ff48bf5SDavid du Colombier }
313ff48bf5SDavid du Colombier
323ff48bf5SDavid du Colombier // make kinv positive
33*39734e7eSDavid du Colombier mpmod(kinv, pub->q, kinv);
343ff48bf5SDavid du Colombier
353ff48bf5SDavid du Colombier // r = ((alpha**k) mod p) mod q
363ff48bf5SDavid du Colombier mpexp(alpha, k, p, r);
373ff48bf5SDavid du Colombier mpmod(r, q, r);
383ff48bf5SDavid du Colombier
393ff48bf5SDavid du Colombier // s = (kinv*(m + ar)) mod q
403ff48bf5SDavid du Colombier mpmul(r, priv->secret, s);
413ff48bf5SDavid du Colombier mpadd(s, m, s);
423ff48bf5SDavid du Colombier mpmul(s, kinv, s);
433ff48bf5SDavid du Colombier mpmod(s, q, s);
443ff48bf5SDavid du Colombier
453ff48bf5SDavid du Colombier sig = dsasigalloc();
463ff48bf5SDavid du Colombier sig->r = r;
473ff48bf5SDavid du Colombier sig->s = s;
483ff48bf5SDavid du Colombier mpfree(qm1);
493ff48bf5SDavid du Colombier mpfree(k);
503ff48bf5SDavid du Colombier mpfree(kinv);
513ff48bf5SDavid du Colombier return sig;
523ff48bf5SDavid du Colombier }
53