71 lines
1.4 KiB
C
71 lines
1.4 KiB
C
#include "os.h"
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#include <mp.h>
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#include <libsec.h>
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RSApriv*
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rsagen(int nlen, int elen, int rounds)
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{
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mpint *p, *q, *e, *d, *phi, *n, *t1, *t2, *kp, *kq, *c2;
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RSApriv *rsa;
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p = mpnew(nlen/2);
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q = mpnew(nlen/2);
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n = mpnew(nlen);
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e = mpnew(elen);
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d = mpnew(0);
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phi = mpnew(nlen);
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// create the prime factors and euclid's function
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genprime(p, nlen/2, rounds);
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genprime(q, nlen - mpsignif(p) + 1, rounds);
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mpmul(p, q, n);
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mpsub(p, mpone, e);
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mpsub(q, mpone, d);
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mpmul(e, d, phi);
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// find an e relatively prime to phi
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t1 = mpnew(0);
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t2 = mpnew(0);
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mprand(elen, genrandom, e);
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if(mpcmp(e,mptwo) <= 0)
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itomp(3, e);
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// See Menezes et al. p.291 "8.8 Note (selecting primes)" for discussion
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// of the merits of various choices of primes and exponents. e=3 is a
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// common and recommended exponent, but doesn't necessarily work here
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// because we chose strong rather than safe primes.
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for(;;){
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mpextendedgcd(e, phi, t1, d, t2);
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if(mpcmp(t1, mpone) == 0)
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break;
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mpadd(mpone, e, e);
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}
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mpfree(t1);
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mpfree(t2);
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// compute chinese remainder coefficient
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c2 = mpnew(0);
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mpinvert(p, q, c2);
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// for crt a**k mod p == (a**(k mod p-1)) mod p
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kq = mpnew(0);
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kp = mpnew(0);
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mpsub(p, mpone, phi);
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mpmod(d, phi, kp);
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mpsub(q, mpone, phi);
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mpmod(d, phi, kq);
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rsa = rsaprivalloc();
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rsa->pub.ek = e;
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rsa->pub.n = n;
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rsa->dk = d;
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rsa->kp = kp;
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rsa->kq = kq;
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rsa->p = p;
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rsa->q = q;
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rsa->c2 = c2;
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mpfree(phi);
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return rsa;
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}
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