trsagen.c - plan9port - [fork] Plan 9 from user space
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       ---
       trsagen.c (1486B)
       ---
            1 #include "os.h"
            2 #include <mp.h>
            3 #include <libsec.h>
            4 
            5 RSApriv*
            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 }