1 #include "os.h"
2 #include <mp.h>
3 #include <libsec.h>
4 
5 /* NIST algorithm for generating DSA primes */
6 /* Menezes et al (1997) Handbook of Applied Cryptography, p.151 */
7 /* q is a 160-bit prime;  p is a 1024-bit prime;  q divides p-1 */
8 
9 /* arithmetic on unsigned ints mod 2**160, represented */
10 /*    as 20-byte, little-endian uchar array */
11 
12 static void
13 Hrand(uchar *s)
14 {
15 	uint32 *u = (uint32*)s;
16 	*u++ = fastrand();
17 	*u++ = fastrand();
18 	*u++ = fastrand();
19 	*u++ = fastrand();
20 	*u = fastrand();
21 }
22 
23 static void
24 Hincr(uchar *s)
25 {
26 	int i;
27 	for(i=0; i<20; i++)
28 		if(++s[i]!=0)
29 			break;
30 }
31 
32 /* this can run for quite a while;  be patient */
33 void
34 DSAprimes(mpint *q, mpint *p, uchar seed[SHA1dlen])
35 {
36 	int i, j, k, n = 6, b = 63;
37 	uchar s[SHA1dlen], Hs[SHA1dlen], Hs1[SHA1dlen], sj[SHA1dlen], sjk[SHA1dlen];
38 	mpint *two1023, *mb, *Vk, *W, *X, *q2;
39 
40 	two1023 = mpnew(1024);
41 	mpleft(mpone, 1023, two1023);
42 	mb = mpnew(0);
43 	mpleft(mpone, b, mb);
44 	W = mpnew(1024);
45 	Vk = mpnew(1024);
46 	X = mpnew(0);
47 	q2 = mpnew(0);
48 forever:
49 	do{
50 		Hrand(s);
51 		memcpy(sj, s, 20);
52 		sha1(s, 20, Hs, 0);
53 		Hincr(sj);
54 		sha1(sj, 20, Hs1, 0);
55 		for(i=0; i<20; i++)
56 			Hs[i] ^= Hs1[i];
57 		Hs[0] |= 1;
58 		Hs[19] |= 0x80;
59 		letomp(Hs, 20, q);
60 	}while(!probably_prime(q, 18));
61 	if(seed != nil)	/* allow skeptics to confirm computation */
62 		memmove(seed, s, SHA1dlen);
63 	i = 0;
64 	j = 2;
65 	Hincr(sj);
66 	mpleft(q, 1, q2);
67 	while(i<4096){
68 		memcpy(sjk, sj, 20);
69 		for(k=0; k <= n; k++){
70 			sha1(sjk, 20, Hs, 0);
71 			letomp(Hs, 20, Vk);
72 			if(k == n)
73 				mpmod(Vk, mb, Vk);
74 			mpleft(Vk, 160*k, Vk);
75 			mpadd(W, Vk, W);
76 			Hincr(sjk);
77 		}
78 		mpadd(W, two1023, X);
79 		mpmod(X, q2, W);
80 		mpsub(W, mpone, W);
81 		mpsub(X, W, p);
82 		if(mpcmp(p, two1023)>=0 && probably_prime(p, 5))
83 			goto done;
84 		i += 1;
85 		j += n+1;
86 		for(k=0; k<n+1; k++)
87 			Hincr(sj);
88 	}
89 	goto forever;
90 done:
91 	mpfree(q2);
92 	mpfree(X);
93 	mpfree(Vk);
94 	mpfree(W);
95 	mpfree(mb);
96 	mpfree(two1023);
97 }