1 #include "os.h"
2 #include <mp.h>
3 #include <libsec.h>
4
5 RSApriv*
rsagen(int nlen,int elen,int rounds)6 rsagen(int nlen, int elen, int rounds)
7 {
8 mpint *p, *q, *e, *d, *phi, *n, *t1, *t2, *kp, *kq, *c2;
9 RSApriv *rsa;
10
11 p = mpnew(nlen/2);
12 q = mpnew(nlen/2);
13 n = mpnew(nlen);
14 e = mpnew(elen);
15 d = mpnew(0);
16 phi = mpnew(nlen);
17
18 // create the prime factors and euclid's function
19 genprime(p, nlen/2, rounds);
20 genprime(q, nlen - mpsignif(p) + 1, rounds);
21 mpmul(p, q, n);
22 mpsub(p, mpone, e);
23 mpsub(q, mpone, d);
24 mpmul(e, d, phi);
25
26 // find an e relatively prime to phi
27 t1 = mpnew(0);
28 t2 = mpnew(0);
29 mprand(elen, genrandom, e);
30 if(mpcmp(e,mptwo) <= 0)
31 itomp(3, e);
32 // See Menezes et al. p.291 "8.8 Note (selecting primes)" for discussion
33 // of the merits of various choices of primes and exponents. e=3 is a
34 // common and recommended exponent, but doesn't necessarily work here
35 // because we chose strong rather than safe primes.
36 for(;;){
37 mpextendedgcd(e, phi, t1, d, t2);
38 if(mpcmp(t1, mpone) == 0)
39 break;
40 mpadd(mpone, e, e);
41 }
42 mpfree(t1);
43 mpfree(t2);
44
45 // compute chinese remainder coefficient
46 c2 = mpnew(0);
47 mpinvert(p, q, c2);
48
49 // for crt a**k mod p == (a**(k mod p-1)) mod p
50 kq = mpnew(0);
51 kp = mpnew(0);
52 mpsub(p, mpone, phi);
53 mpmod(d, phi, kp);
54 mpsub(q, mpone, phi);
55 mpmod(d, phi, kq);
56
57 rsa = rsaprivalloc();
58 rsa->pub.ek = e;
59 rsa->pub.n = n;
60 rsa->dk = d;
61 rsa->kp = kp;
62 rsa->kq = kq;
63 rsa->p = p;
64 rsa->q = q;
65 rsa->c2 = c2;
66
67 mpfree(phi);
68
69 return rsa;
70 }
71