53 lines
934 B
C
53 lines
934 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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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, qm1) >= 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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continue;
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break;
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}
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// make kinv positive
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mpmod(kinv, qm1, 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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}
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