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