Subversion Repositories planix.SVN

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

// decrypt rsa using garner's algorithm for the chinese remainder theorem
//      seminumerical algorithms, knuth, pp 253-254
//      applied cryptography, menezes et al, pg 612
mpint*
rsadecrypt(RSApriv *rsa, mpint *in, mpint *out)
{
        mpint *v1, *v2;

        if(out == nil)
                out = mpnew(0);

        // convert in to modular representation
        v1 = mpnew(0);
        mpmod(in, rsa->p, v1);
        v2 = mpnew(0);
        mpmod(in, rsa->q, v2);

        // exponentiate the modular rep
        mpexp(v1, rsa->kp, rsa->p, v1);
        mpexp(v2, rsa->kq, rsa->q, v2);
        
        // out = v1 + p*((v2-v1)*c2 mod q)
        mpsub(v2, v1, v2);
        mpmul(v2, rsa->c2, v2);
        mpmod(v2, rsa->q, v2);
        mpmul(v2, rsa->p, out);
        mpadd(v1, out, out);

        mpfree(v1);
        mpfree(v2);

        return out;
}