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Code Issues Releases Activity

ElGamalEncryptor added

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This commit is contained in:
orignal 2014-02-20 12:25:28 -05:00
parent 345be142ae
commit b14cdc8052
1 changed files with 64 additions and 18 deletions
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82
ElGamal.h
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@ -12,6 +12,70 @@ namespace i2p
{
namespace crypto
{
class ElGamalEncryptor
{
public:
ElGamalEncryptor (const uint8_t * key, bool zeroPadding = false):
y (key, 256), k (rnd, CryptoPP::Integer::One(), elgp-1),
a (a_exp_b_mod_c (elgg, k, elgp)), b1 (a_exp_b_mod_c (y, k, elgp)),
m_ZeroPadding (zeroPadding)
{
}
void Encrypt (const uint8_t * data, int len, uint8_t * encrypted)
{
// calculate b = b1*m mod p
uint8_t m[255];
m[0] = 0xFF;
memcpy (m+33, data, len);
CryptoPP::SHA256().CalculateDigest(m+1, m+33, 222);
CryptoPP::Integer b (a_times_b_mod_c (b1, CryptoPP::Integer (m, 255), elgp));
// copy a and b
if (m_ZeroPadding)
{
encrypted[0] = 0;
a.Encode (encrypted + 1, 256);
encrypted[257] = 0;
b.Encode (encrypted + 258, 256);
}
else
{
a.Encode (encrypted, 256);
b.Encode (encrypted + 256, 256);
}
}
private:
CryptoPP::AutoSeededRandomPool rnd;
CryptoPP::Integer y, k, a, b1;
bool m_ZeroPadding;
};
inline bool ElGamalDecrypt (const uint8_t * key, const uint8_t * encrypted,
uint8_t * data, bool zeroPadding = false)
{
CryptoPP::Integer x(key, 256), a(zeroPadding? encrypted +1 : encrypted, 256),
b(zeroPadding? encrypted + 258 :encrypted + 256, 256);
uint8_t m[255], hash[32];
a_times_b_mod_c (b, a_exp_b_mod_c (a, elgp - x - 1, elgp), elgp).Encode (m, 255);
CryptoPP::SHA256().CalculateDigest(hash, m+33, 222);
for (int i = 0; i < 32; i++)
if (hash[i] != m[i+1])
{
LogPrint ("ElGamal decrypt hash doesn't match");
return false;
}
memcpy (data, m + 33, 222);
return true;
}
// deprecated
inline void ElGamalEncrypt (const uint8_t * key, const uint8_t * data, int len,
uint8_t * encrypted, bool zeroPadding = false) // 514 with padding and 512 without
{
@ -31,24 +95,6 @@ namespace crypto
a_times_b_mod_c (a_exp_b_mod_c (y, k, elgp),
CryptoPP::Integer (m, 255), elgp).Encode (zeroPadding ? encrypted + 258 : encrypted + 256, 256);
}
inline bool ElGamalDecrypt (const uint8_t * key, const uint8_t * encrypted,
uint8_t * data, bool zeroPadding = false)
{
CryptoPP::Integer x(key, 256), a(zeroPadding? encrypted +1 : encrypted, 256),
b(zeroPadding? encrypted + 258 :encrypted + 256, 256);
uint8_t m[255], hash[32];
a_times_b_mod_c (b, a_exp_b_mod_c (a, elgp - x - 1, elgp), elgp).Encode (m, 255);
CryptoPP::SHA256().CalculateDigest(hash, m+33, 222);
for (int i = 0; i < 32; i++)
if (hash[i] != m[i+1])
{
LogPrint ("ElGamal decrypt hash doesn't match");
return false;
}
memcpy (data, m + 33, 222);
return true;
}
}
}