Subversion Repositories planix.SVN

#include "os.h"
#include <mp.h>
#include <libsec.h>

RSApriv*
rsagen(int nlen, int elen, int rounds)
{
        mpint *p, *q, *e, *d, *phi, *n, *t1, *t2, *kp, *kq, *c2;
        RSApriv *rsa;

        p = mpnew(nlen/2);
        q = mpnew(nlen/2);
        n = mpnew(nlen);
        e = mpnew(elen);
        d = mpnew(0);
        phi = mpnew(nlen);

        // create the prime factors and euclid's function
        genprime(p, nlen/2, rounds);
        genprime(q, nlen - mpsignif(p) + 1, rounds);
        mpmul(p, q, n);
        mpsub(p, mpone, e);
        mpsub(q, mpone, d);
        mpmul(e, d, phi);

        // find an e relatively prime to phi
        t1 = mpnew(0);
        t2 = mpnew(0);
        if(elen == 0)
                itomp(65537, e);
        else {
                mprand(elen, genrandom, e);
                if(mpcmp(e,mptwo) <= 0)
                        itomp(3, e);
        }
        // See Menezes et al. p.291 "8.8 Note (selecting primes)" for discussion
        // of the merits of various choices of primes and exponents.  e=3 is a
        // common and recommended exponent, but doesn't necessarily work here
        // because we chose strong rather than safe primes.
        for(;;){
                mpextendedgcd(e, phi, t1, d, t2);
                if(mpcmp(t1, mpone) == 0)
                        break;
                mpadd(mpone, e, e);
        }
        if(d->sign < 0)
                mpadd(phi, d, d);
        mpfree(t1);
        mpfree(t2);

        // compute chinese remainder coefficient
        c2 = mpnew(0);
        mpinvert(p, q, c2);

        // for crt a**k mod p == (a**(k mod p-1)) mod p
        kq = mpnew(0);
        kp = mpnew(0);
        mpsub(p, mpone, phi);
        mpmod(d, phi, kp);
        mpsub(q, mpone, phi);
        mpmod(d, phi, kq);

        rsa = rsaprivalloc();
        rsa->pub.ek = e;
        rsa->pub.n = n;
        rsa->dk = d;
        rsa->kp = kp;
        rsa->kq = kq;
        rsa->p = p;
        rsa->q = q;
        rsa->c2 = c2;

        mpfree(phi);

        return rsa;
}