From b14cdc80529f5c376a3131405a84415fb4dea61c Mon Sep 17 00:00:00 2001
From: orignal <romakoshelkin@yandex.ru>
Date: Thu, 20 Feb 2014 12:25:28 -0500
Subject: [PATCH] ElGamalEncryptor added

---
 ElGamal.h | 82 +++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 64 insertions(+), 18 deletions(-)

diff --git a/ElGamal.h b/ElGamal.h
index 387e02bb..ca82f19a 100644
--- a/ElGamal.h
+++ b/ElGamal.h
@@ -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;
-	}	
 }
 }