From 63677cc8753d925b1f1e0c75b0e06ebbc3db0b27 Mon Sep 17 00:00:00 2001
From: orignal <romakoshelkin@yandex.ru>
Date: Sun, 1 Sep 2013 13:45:06 -0400
Subject: [PATCH] ElGamal added

---
 ElGamal.h | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 ElGamal.h

diff --git a/ElGamal.h b/ElGamal.h
new file mode 100644
index 00000000..f9b5ff65
--- /dev/null
+++ b/ElGamal.h
@@ -0,0 +1,47 @@
+#ifndef EL_GAMAL_H__
+#define EL_GAMAL_H__
+
+#include <inttypes.h>
+#include <cryptopp/integer.h>
+#include <cryptopp/osrng.h>
+#include <cryptopp/sha.h>
+#include "CryptoConst.h"
+#include "Log.h"
+
+namespace i2p
+{
+namespace crypto
+{
+	inline void ElGamalEncrypt (const uint8_t * key, const uint8_t * data, int len, uint8_t * encrypted)
+	{
+		CryptoPP::AutoSeededRandomPool rnd;		
+		CryptoPP::Integer y(key, 256), k(rnd, CryptoPP::Integer::One(), elgp-1);
+
+		a_exp_b_mod_c (elgg, k, elgp).Encode (encrypted, 256);
+		uint8_t m[255];
+		m[0] = 0xFF;
+		memcpy (m+33, data, len);
+		CryptoPP::SHA256().CalculateDigest(m+1, m+33, 222);
+		a_times_b_mod_c (a_exp_b_mod_c (y, k, elgp), 
+			CryptoPP::Integer (m, 255), elgp).Encode (encrypted + 256, 256);
+	}	
+
+	inline bool ElGamalDecrypt (const uint8_t * key, const uint8_t * encrypted, uint8_t * data)
+	{
+		CryptoPP::Integer x(key, 256), a(encrypted, 256), b(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;
+	}	
+}
+}	
+
+#endif