47 lines
909 B
C
47 lines
909 B
C
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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(sig->r->sign < 0 || mpcmp(sig->r, pub->q) >= 0)
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return rv;
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if(sig->s->sign < 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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}
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