1 files changed, 135 insertions, 0 deletions
diff --git a/lib/pubkey/elgamal/elgamal.cpp b/lib/pubkey/elgamal/elgamal.cpp
new file mode 100644
index 000000000..c8a9ba9d0
--- /dev/null
+++ b/lib/pubkey/elgamal/elgamal.cpp
@@ -0,0 +1,135 @@
+/*
+* ElGamal
+* (C) 1999-2007 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/elgamal.h>
+#include <botan/numthry.h>
+#include <botan/keypair.h>
+#include <botan/workfactor.h>
+
+namespace Botan {
+
+/*
+* ElGamal_PublicKey Constructor
+*/
+ElGamal_PublicKey::ElGamal_PublicKey(const DL_Group& grp, const BigInt& y1)
+   {
+   group = grp;
+   y = y1;
+   }
+
+/*
+* ElGamal_PrivateKey Constructor
+*/
+ElGamal_PrivateKey::ElGamal_PrivateKey(RandomNumberGenerator& rng,
+                                       const DL_Group& grp,
+                                       const BigInt& x_arg)
+   {
+   group = grp;
+   x = x_arg;
+
+   if(x == 0)
+      x.randomize(rng, 2 * dl_work_factor(group_p().bits()));
+
+   y = power_mod(group_g(), x, group_p());
+
+   if(x_arg == 0)
+      gen_check(rng);
+   else
+      load_check(rng);
+   }
+
+ElGamal_PrivateKey::ElGamal_PrivateKey(const AlgorithmIdentifier& alg_id,
+                                       const secure_vector<byte>& key_bits,
+                                       RandomNumberGenerator& rng) :
+   DL_Scheme_PrivateKey(alg_id, key_bits, DL_Group::ANSI_X9_42)
+   {
+   y = power_mod(group_g(), x, group_p());
+   load_check(rng);
+   }
+
+/*
+* Check Private ElGamal Parameters
+*/
+bool ElGamal_PrivateKey::check_key(RandomNumberGenerator& rng,
+                                   bool strong) const
+   {
+   if(!DL_Scheme_PrivateKey::check_key(rng, strong))
+      return false;
+
+   if(!strong)
+      return true;
+
+   return KeyPair::encryption_consistency_check(rng, *this, "EME1(SHA-1)");
+   }
+
+ElGamal_Encryption_Operation::ElGamal_Encryption_Operation(const ElGamal_PublicKey& key)
+   {
+   const BigInt& p = key.group_p();
+
+   powermod_g_p = Fixed_Base_Power_Mod(key.group_g(), p);
+   powermod_y_p = Fixed_Base_Power_Mod(key.get_y(), p);
+   mod_p = Modular_Reducer(p);
+   }
+
+secure_vector<byte>
+ElGamal_Encryption_Operation::encrypt(const byte msg[], size_t msg_len,
+                                      RandomNumberGenerator& rng)
+   {
+   const BigInt& p = mod_p.get_modulus();
+
+   BigInt m(msg, msg_len);
+
+   if(m >= p)
+      throw Invalid_Argument("ElGamal encryption: Input is too large");
+
+   BigInt k(rng, 2 * dl_work_factor(p.bits()));
+
+   BigInt a = powermod_g_p(k);
+   BigInt b = mod_p.multiply(m, powermod_y_p(k));
+
+   secure_vector<byte> output(2*p.bytes());
+   a.binary_encode(&output[p.bytes() - a.bytes()]);
+   b.binary_encode(&output[output.size() / 2 + (p.bytes() - b.bytes())]);
+   return output;
+   }
+
+ElGamal_Decryption_Operation::ElGamal_Decryption_Operation(const ElGamal_PrivateKey& key,
+                                                           RandomNumberGenerator& rng)
+   {
+   const BigInt& p = key.group_p();
+
+   powermod_x_p = Fixed_Exponent_Power_Mod(key.get_x(), p);
+   mod_p = Modular_Reducer(p);
+
+   BigInt k(rng, p.bits() - 1);
+   blinder = Blinder(k, powermod_x_p(k), p);
+   }
+
+secure_vector<byte>
+ElGamal_Decryption_Operation::decrypt(const byte msg[], size_t msg_len)
+   {
+   const BigInt& p = mod_p.get_modulus();
+
+   const size_t p_bytes = p.bytes();
+
+   if(msg_len != 2 * p_bytes)
+      throw Invalid_Argument("ElGamal decryption: Invalid message");
+
+   BigInt a(msg, p_bytes);
+   BigInt b(msg + p_bytes, p_bytes);
+
+   if(a >= p || b >= p)
+      throw Invalid_Argument("ElGamal decryption: Invalid message");
+
+   a = blinder.blind(a);
+
+   BigInt r = mod_p.multiply(b, inverse_mod(powermod_x_p(a), p));
+
+   return BigInt::encode_locked(blinder.unblind(r));
+   }
+
+}