1*8ccd4a63SDavid du Colombier #include "os.h"
2*8ccd4a63SDavid du Colombier #include <mp.h>
3*8ccd4a63SDavid du Colombier #include <libsec.h>
4*8ccd4a63SDavid du Colombier
5*8ccd4a63SDavid du Colombier DSAsig*
dsasign(DSApriv * priv,mpint * m)6*8ccd4a63SDavid du Colombier dsasign(DSApriv *priv, mpint *m)
7*8ccd4a63SDavid du Colombier {
8*8ccd4a63SDavid du Colombier DSApub *pub = &priv->pub;
9*8ccd4a63SDavid du Colombier DSAsig *sig;
10*8ccd4a63SDavid du Colombier mpint *qm1, *k, *kinv, *r, *s;
11*8ccd4a63SDavid du Colombier mpint *q = pub->q, *p = pub->p, *alpha = pub->alpha;
12*8ccd4a63SDavid du Colombier int qlen = mpsignif(q);
13*8ccd4a63SDavid du Colombier
14*8ccd4a63SDavid du Colombier qm1 = mpnew(0);
15*8ccd4a63SDavid du Colombier kinv = mpnew(0);
16*8ccd4a63SDavid du Colombier r = mpnew(0);
17*8ccd4a63SDavid du Colombier s = mpnew(0);
18*8ccd4a63SDavid du Colombier k = mpnew(0);
19*8ccd4a63SDavid du Colombier mpsub(pub->q, mpone, qm1);
20*8ccd4a63SDavid du Colombier
21*8ccd4a63SDavid du Colombier // find a k that has an inverse mod q
22*8ccd4a63SDavid du Colombier while(1){
23*8ccd4a63SDavid du Colombier mprand(qlen, genrandom, k);
24*8ccd4a63SDavid du Colombier if((mpcmp(mpone, k) > 0) || (mpcmp(k, qm1) >= 0))
25*8ccd4a63SDavid du Colombier continue;
26*8ccd4a63SDavid du Colombier mpextendedgcd(k, q, r, kinv, s);
27*8ccd4a63SDavid du Colombier if(mpcmp(r, mpone) != 0)
28*8ccd4a63SDavid du Colombier continue;
29*8ccd4a63SDavid du Colombier break;
30*8ccd4a63SDavid du Colombier }
31*8ccd4a63SDavid du Colombier
32*8ccd4a63SDavid du Colombier // make kinv positive
33*8ccd4a63SDavid du Colombier mpmod(kinv, qm1, kinv);
34*8ccd4a63SDavid du Colombier
35*8ccd4a63SDavid du Colombier // r = ((alpha**k) mod p) mod q
36*8ccd4a63SDavid du Colombier mpexp(alpha, k, p, r);
37*8ccd4a63SDavid du Colombier mpmod(r, q, r);
38*8ccd4a63SDavid du Colombier
39*8ccd4a63SDavid du Colombier // s = (kinv*(m + ar)) mod q
40*8ccd4a63SDavid du Colombier mpmul(r, priv->secret, s);
41*8ccd4a63SDavid du Colombier mpadd(s, m, s);
42*8ccd4a63SDavid du Colombier mpmul(s, kinv, s);
43*8ccd4a63SDavid du Colombier mpmod(s, q, s);
44*8ccd4a63SDavid du Colombier
45*8ccd4a63SDavid du Colombier sig = dsasigalloc();
46*8ccd4a63SDavid du Colombier sig->r = r;
47*8ccd4a63SDavid du Colombier sig->s = s;
48*8ccd4a63SDavid du Colombier mpfree(qm1);
49*8ccd4a63SDavid du Colombier mpfree(k);
50*8ccd4a63SDavid du Colombier mpfree(kinv);
51*8ccd4a63SDavid du Colombier return sig;
52*8ccd4a63SDavid du Colombier }
53