1 0fc65b37 2004-03-21 devnull #include "os.h"
 2 0fc65b37 2004-03-21 devnull #include <mp.h>
 3 0fc65b37 2004-03-21 devnull #include <libsec.h>
 4 0fc65b37 2004-03-21 devnull 
 5 0fc65b37 2004-03-21 devnull // decrypt rsa using garner's algorithm for the chinese remainder theorem
 6 0fc65b37 2004-03-21 devnull //	seminumerical algorithms, knuth, pp 253-254
 7 0fc65b37 2004-03-21 devnull //	applied cryptography, menezes et al, pg 612
 8 0fc65b37 2004-03-21 devnull mpint*
 9 0fc65b37 2004-03-21 devnull rsadecrypt(RSApriv *rsa, mpint *in, mpint *out)
10 0fc65b37 2004-03-21 devnull {
11 0fc65b37 2004-03-21 devnull 	mpint *v1, *v2;
12 0fc65b37 2004-03-21 devnull 
13 0fc65b37 2004-03-21 devnull 	if(out == nil)
14 0fc65b37 2004-03-21 devnull 		out = mpnew(0);
15 0fc65b37 2004-03-21 devnull 
16 0fc65b37 2004-03-21 devnull 	// convert in to modular representation
17 0fc65b37 2004-03-21 devnull 	v1 = mpnew(0);
18 0fc65b37 2004-03-21 devnull 	mpmod(in, rsa->p, v1);
19 0fc65b37 2004-03-21 devnull 	v2 = mpnew(0);
20 0fc65b37 2004-03-21 devnull 	mpmod(in, rsa->q, v2);
21 0fc65b37 2004-03-21 devnull 
22 0fc65b37 2004-03-21 devnull 	// exponentiate the modular rep
23 0fc65b37 2004-03-21 devnull 	mpexp(v1, rsa->kp, rsa->p, v1);
24 0fc65b37 2004-03-21 devnull 	mpexp(v2, rsa->kq, rsa->q, v2);
25 0fc65b37 2004-03-21 devnull 	
26 0fc65b37 2004-03-21 devnull 	// out = v1 + p*((v2-v1)*c2 mod q)
27 0fc65b37 2004-03-21 devnull 	mpsub(v2, v1, v2);
28 0fc65b37 2004-03-21 devnull 	mpmul(v2, rsa->c2, v2);
29 0fc65b37 2004-03-21 devnull 	mpmod(v2, rsa->q, v2);
30 0fc65b37 2004-03-21 devnull 	mpmul(v2, rsa->p, out);
31 0fc65b37 2004-03-21 devnull 	mpadd(v1, out, out);
32 0fc65b37 2004-03-21 devnull 
33 0fc65b37 2004-03-21 devnull 	mpfree(v1);
34 0fc65b37 2004-03-21 devnull 	mpfree(v2);
35 0fc65b37 2004-03-21 devnull 
36 0fc65b37 2004-03-21 devnull 	return out;
37 0fc65b37 2004-03-21 devnull }