Add crypto/ directory.

crypto/ElGamal.h

@@ -0,0 +1,87 @@
+#ifndef EL_GAMAL_H__
+#define EL_GAMAL_H__
+
+#include <inttypes.h>
+#include <cryptopp/integer.h>
+#include <cryptopp/osrng.h>
+#include <cryptopp/dh.h>
+#include <cryptopp/sha.h>
+#include "CryptoConst.h"
+#include "Log.h"
+
+namespace i2p
+{
+namespace crypto
+{
+
+    class ElGamalEncryption
+    {
+        public:
+
+            ElGamalEncryption (const uint8_t * key)
+            {
+                CryptoPP::AutoSeededRandomPool rnd; 
+                CryptoPP::Integer 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);
+            }
+
+            void Encrypt (const uint8_t * data, int len, uint8_t * encrypted, bool zeroPadding = false) const
+            {
+                // 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 (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::Integer a, b1;    
+    };
+
+    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];
+        a_times_b_mod_c (b, a_exp_b_mod_c (a, elgp - x - 1, elgp), elgp).Encode (m, 255);
+        if (!CryptoPP::SHA256().VerifyDigest (m + 1, m + 33, 222))
+        {
+            LogPrint ("ElGamal decrypt hash doesn't match");
+            return false;
+        }
+        memcpy (data, m + 33, 222);
+        return true;
+    }   
+
+    inline void GenerateElGamalKeyPair (CryptoPP::RandomNumberGenerator& rnd, uint8_t * priv, uint8_t * pub)
+    {
+#if defined(__x86_64__) || defined(__i386__) || defined(_MSC_VER)   
+        rnd.GenerateBlock (priv, 256);
+        a_exp_b_mod_c (elgg, CryptoPP::Integer (priv, 256), elgp).Encode (pub, 256);
+#else
+        CryptoPP::DH dh (elgp, elgg);
+        dh.GenerateKeyPair(rnd, priv, pub); 
+#endif      
+    }   
+}
+}   
+
+#endif