dsasign.c (981B)
1 #include "os.h" 2 #include <mp.h> 3 #include <libsec.h> 4 5 DSAsig* 6 dsasign(DSApriv *priv, mpint *m) 7 { 8 DSApub *pub = &priv->pub; 9 DSAsig *sig; 10 mpint *qm1, *k, *kinv, *r, *s; 11 mpint *q = pub->q, *p = pub->p, *alpha = pub->alpha; 12 int qlen = mpsignif(q); 13 14 qm1 = mpnew(0); 15 kinv = mpnew(0); 16 r = mpnew(0); 17 s = mpnew(0); 18 k = mpnew(0); 19 mpsub(pub->q, mpone, qm1); 20 21 /* find a k that has an inverse mod q */ 22 while(1){ 23 mprand(qlen, genrandom, k); 24 if((mpcmp(mpone, k) > 0) || (mpcmp(k, pub->q) >= 0)) 25 continue; 26 mpextendedgcd(k, q, r, kinv, s); 27 if(mpcmp(r, mpone) != 0) 28 sysfatal("dsasign: pub->q not prime"); 29 break; 30 } 31 32 /* make kinv positive */ 33 mpmod(kinv, pub->q, kinv); 34 35 /* r = ((alpha**k) mod p) mod q */ 36 mpexp(alpha, k, p, r); 37 mpmod(r, q, r); 38 39 /* s = (kinv*(m + ar)) mod q */ 40 mpmul(r, priv->secret, s); 41 mpadd(s, m, s); 42 mpmul(s, kinv, s); 43 mpmod(s, q, s); 44 45 sig = dsasigalloc(); 46 sig->r = r; 47 sig->s = s; 48 mpfree(qm1); 49 mpfree(k); 50 mpfree(kinv); 51 return sig; 52 }