37 lines
741 B
C
37 lines
741 B
C
#include "os.h"
|
|
#include <mp.h>
|
|
#include <libsec.h>
|
|
|
|
// find a prime p of length n and a generator alpha of Z^*_p
|
|
// Alg 4.86 Menezes et al () Handbook, p.164
|
|
void
|
|
gensafeprime(mpint *p, mpint *alpha, int n, int accuracy)
|
|
{
|
|
mpint *q, *b;
|
|
|
|
q = mpnew(n-1);
|
|
while(1){
|
|
genprime(q, n-1, accuracy);
|
|
mpleft(q, 1, p);
|
|
mpadd(p, mpone, p); // p = 2*q+1
|
|
if(probably_prime(p, accuracy))
|
|
break;
|
|
}
|
|
// now find a generator alpha of the multiplicative
|
|
// group Z*_p of order p-1=2q
|
|
b = mpnew(0);
|
|
while(1){
|
|
mprand(n, genrandom, alpha);
|
|
mpmod(alpha, p, alpha);
|
|
mpmul(alpha, alpha, b);
|
|
mpmod(b, p, b);
|
|
if(mpcmp(b, mpone) == 0)
|
|
continue;
|
|
mpexp(alpha, q, p, b);
|
|
if(mpcmp(b, mpone) != 0)
|
|
break;
|
|
}
|
|
mpfree(b);
|
|
mpfree(q);
|
|
}
|