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#include "os.h"
#include <mp.h>
#include <libsec.h>
DSAsig*
dsasign(DSApriv *priv, mpint *m)
{
DSApub *pub = &priv->pub;
DSAsig *sig;
mpint *qm1, *k, *kinv, *r, *s;
mpint *q = pub->q, *p = pub->p, *alpha = pub->alpha;
int qlen = mpsignif(q);
qm1 = mpnew(0);
kinv = mpnew(0);
r = mpnew(0);
s = mpnew(0);
k = mpnew(0);
mpsub(pub->q, mpone, qm1);
/* find a k that has an inverse mod q */
while(1){
mprand(qlen, genrandom, k);
if((mpcmp(mpone, k) > 0) || (mpcmp(k, pub->q) >= 0))
continue;
mpextendedgcd(k, q, r, kinv, s);
if(mpcmp(r, mpone) != 0)
sysfatal("dsasign: pub->q not prime");
break;
}
/* make kinv positive */
mpmod(kinv, pub->q, kinv);
/* r = ((alpha**k) mod p) mod q */
mpexp(alpha, k, p, r);
mpmod(r, q, r);
/* s = (kinv*(m + ar)) mod q */
mpmul(r, priv->secret, s);
mpadd(s, m, s);
mpmul(s, kinv, s);
mpmod(s, q, s);
sig = dsasigalloc();
sig->r = r;
sig->s = s;
mpfree(qm1);
mpfree(k);
mpfree(kinv);
return sig;
}
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