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78 lines
1.8 KiB
C++
78 lines
1.8 KiB
C++
#ifndef EL_GAMAL_H__
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#define EL_GAMAL_H__
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#include <inttypes.h>
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#include <cryptopp/integer.h>
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#include <cryptopp/osrng.h>
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#include <cryptopp/sha.h>
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#include "CryptoConst.h"
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#include "Log.h"
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namespace i2p
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{
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namespace crypto
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{
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class ElGamalEncryption
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{
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public:
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ElGamalEncryption (const uint8_t * key):
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y (key, 256), k (rnd, CryptoPP::Integer::One(), elgp-1),
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a (a_exp_b_mod_c (elgg, k, elgp)), b1 (a_exp_b_mod_c (y, k, elgp))
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{
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}
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void Encrypt (const uint8_t * data, int len, uint8_t * encrypted, bool zeroPadding = false)
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{
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// calculate b = b1*m mod p
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uint8_t m[255];
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m[0] = 0xFF;
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memcpy (m+33, data, len);
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CryptoPP::SHA256().CalculateDigest(m+1, m+33, 222);
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CryptoPP::Integer b (a_times_b_mod_c (b1, CryptoPP::Integer (m, 255), elgp));
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// copy a and b
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if (zeroPadding)
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{
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encrypted[0] = 0;
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a.Encode (encrypted + 1, 256);
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encrypted[257] = 0;
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b.Encode (encrypted + 258, 256);
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}
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else
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{
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a.Encode (encrypted, 256);
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b.Encode (encrypted + 256, 256);
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}
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}
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private:
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CryptoPP::AutoSeededRandomPool rnd;
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CryptoPP::Integer y, k, a, b1;
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bool m_ZeroPadding;
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};
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inline bool ElGamalDecrypt (const uint8_t * key, const uint8_t * encrypted,
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uint8_t * data, bool zeroPadding = false)
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{
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CryptoPP::Integer x(key, 256), a(zeroPadding? encrypted +1 : encrypted, 256),
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b(zeroPadding? encrypted + 258 :encrypted + 256, 256);
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uint8_t m[255], hash[32];
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a_times_b_mod_c (b, a_exp_b_mod_c (a, elgp - x - 1, elgp), elgp).Encode (m, 255);
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CryptoPP::SHA256().CalculateDigest(hash, m+33, 222);
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for (int i = 0; i < 32; i++)
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if (hash[i] != m[i+1])
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{
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LogPrint ("ElGamal decrypt hash doesn't match");
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return false;
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}
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memcpy (data, m + 33, 222);
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return true;
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}
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}
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}
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#endif
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