diff options
Diffstat (limited to 'src/lib/pubkey/elgamal/elgamal.cpp')
-rw-r--r-- | src/lib/pubkey/elgamal/elgamal.cpp | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/src/lib/pubkey/elgamal/elgamal.cpp b/src/lib/pubkey/elgamal/elgamal.cpp new file mode 100644 index 000000000..c8a9ba9d0 --- /dev/null +++ b/src/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)); + } + +} |