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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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int
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dsaverify(DSApub *pub, DSAsig *sig, mpint *m)
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{
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	int rv = -1;
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	mpint *u1, *u2, *v, *sinv;
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	if(mpcmp(sig->r, mpone) < 0 || mpcmp(sig->r, pub->q) >= 0)
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		return rv;
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	if(mpcmp(sig->s, mpone) < 0 || mpcmp(sig->s, pub->q) >= 0)
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		return rv;
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	u1 = mpnew(0);
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	u2 = mpnew(0);
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	v = mpnew(0);
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	sinv = mpnew(0);
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	// find (s**-1) mod q, make sure it exists
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	mpextendedgcd(sig->s, pub->q, u1, sinv, v);
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	if(mpcmp(u1, mpone) != 0)
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		goto out;
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	// u1 = (sinv * m) mod q, u2 = (r * sinv) mod q
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	mpmul(sinv, m, u1);
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	mpmod(u1, pub->q, u1);
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	mpmul(sig->r, sinv, u2);
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	mpmod(u2, pub->q, u2);
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	// v = (((alpha**u1)*(key**u2)) mod p) mod q
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	mpexp(pub->alpha, u1, pub->p, sinv);
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	mpexp(pub->key, u2, pub->p, v);
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	mpmul(sinv, v, v);
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	mpmod(v, pub->p, v);
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	mpmod(v, pub->q, v);
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	if(mpcmp(v, sig->r) == 0)
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		rv = 0;
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out:
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	mpfree(v);
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	mpfree(u1);
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	mpfree(u2);
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	mpfree(sinv);
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	return rv;
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}