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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;
- }
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