98 lines
1.9 KiB
C
98 lines
1.9 KiB
C
#include "os.h"
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#include <mp.h>
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#include <libsec.h>
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// NIST algorithm for generating DSA primes
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// Menezes et al (1997) Handbook of Applied Cryptography, p.151
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// q is a 160-bit prime; p is a 1024-bit prime; q divides p-1
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// arithmetic on unsigned ints mod 2**160, represented
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// as 20-byte, little-endian uint8_t array
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static void
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Hrand(uint8_t *s)
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{
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uint32_t *u = (uint32_t*)s;
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*u++ = fastrand();
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*u++ = fastrand();
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*u++ = fastrand();
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*u++ = fastrand();
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*u = fastrand();
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}
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static void
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Hincr(uint8_t *s)
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{
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int i;
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for(i=0; i<20; i++)
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if(++s[i]!=0)
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break;
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}
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// this can run for quite a while; be patient
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void
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DSAprimes(mpint *q, mpint *p, uint8_t seed[SHA1dlen])
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{
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int i, j, k, n = 6, b = 63;
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uint8_t s[SHA1dlen], Hs[SHA1dlen], Hs1[SHA1dlen], sj[SHA1dlen], sjk[SHA1dlen];
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mpint *two1023, *mb, *Vk, *W, *X, *q2;
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two1023 = mpnew(1024);
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mpleft(mpone, 1023, two1023);
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mb = mpnew(0);
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mpleft(mpone, b, mb);
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W = mpnew(1024);
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Vk = mpnew(1024);
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X = mpnew(0);
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q2 = mpnew(0);
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forever:
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do{
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Hrand(s);
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memcpy(sj, s, 20);
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sha1(s, 20, Hs, 0);
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Hincr(sj);
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sha1(sj, 20, Hs1, 0);
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for(i=0; i<20; i++)
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Hs[i] ^= Hs1[i];
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Hs[0] |= 1;
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Hs[19] |= 0x80;
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letomp(Hs, 20, q);
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}while(!probably_prime(q, 18));
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if(seed != nil) // allow skeptics to confirm computation
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memmove(seed, s, SHA1dlen);
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i = 0;
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j = 2;
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Hincr(sj);
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mpleft(q, 1, q2);
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while(i<4096){
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memcpy(sjk, sj, 20);
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for(k=0; k <= n; k++){
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sha1(sjk, 20, Hs, 0);
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letomp(Hs, 20, Vk);
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if(k == n)
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mpmod(Vk, mb, Vk);
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mpleft(Vk, 160*k, Vk);
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mpadd(W, Vk, W);
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Hincr(sjk);
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}
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mpadd(W, two1023, X);
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mpmod(X, q2, W);
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mpsub(W, mpone, W);
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mpsub(X, W, p);
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if(mpcmp(p, two1023)>=0 && probably_prime(p, 5))
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goto done;
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i += 1;
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j += n+1;
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for(k=0; k<n+1; k++)
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Hincr(sj);
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}
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goto forever;
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done:
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mpfree(q2);
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mpfree(X);
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mpfree(Vk);
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mpfree(W);
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mpfree(mb);
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mpfree(two1023);
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}
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