38 lines
749 B
C
38 lines
749 B
C
#include "os.h"
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#include <mp.h>
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#include <libsec.h>
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// decrypt rsa using garner's algorithm for the chinese remainder theorem
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// seminumerical algorithms, knuth, pp 253-254
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// applied cryptography, menezes et al, pg 612
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mpint*
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rsadecrypt(RSApriv *rsa, mpint *in, mpint *out)
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{
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mpint *v1, *v2;
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if(out == nil)
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out = mpnew(0);
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// convert in to modular representation
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v1 = mpnew(0);
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mpmod(in, rsa->p, v1);
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v2 = mpnew(0);
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mpmod(in, rsa->q, v2);
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// exponentiate the modular rep
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mpexp(v1, rsa->kp, rsa->p, v1);
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mpexp(v2, rsa->kq, rsa->q, v2);
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// out = v1 + p*((v2-v1)*c2 mod q)
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mpsub(v2, v1, v2);
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mpmul(v2, rsa->c2, v2);
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mpmod(v2, rsa->q, v2);
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mpmul(v2, rsa->p, out);
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mpadd(v1, out, out);
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mpfree(v1);
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mpfree(v2);
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return out;
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}
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