trsadecrypt.c - plan9port - [fork] Plan 9 from user space
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trsadecrypt.c (766B)
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1 #include "os.h"
2 #include <mp.h>
3 #include <libsec.h>
4
5 /* decrypt rsa using garner's algorithm for the chinese remainder theorem */
6 /* seminumerical algorithms, knuth, pp 253-254 */
7 /* applied cryptography, menezes et al, pg 612 */
8 mpint*
9 rsadecrypt(RSApriv *rsa, mpint *in, mpint *out)
10 {
11 mpint *v1, *v2;
12
13 if(out == nil)
14 out = mpnew(0);
15
16 /* convert in to modular representation */
17 v1 = mpnew(0);
18 mpmod(in, rsa->p, v1);
19 v2 = mpnew(0);
20 mpmod(in, rsa->q, v2);
21
22 /* exponentiate the modular rep */
23 mpexp(v1, rsa->kp, rsa->p, v1);
24 mpexp(v2, rsa->kq, rsa->q, v2);
25
26 /* out = v1 + p*((v2-v1)*c2 mod q) */
27 mpsub(v2, v1, v2);
28 mpmul(v2, rsa->c2, v2);
29 mpmod(v2, rsa->q, v2);
30 mpmul(v2, rsa->p, out);
31 mpadd(v1, out, out);
32
33 mpfree(v1);
34 mpfree(v2);
35
36 return out;
37 }