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#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;

}