diff options
Diffstat (limited to 'botan/src/pubkey/elgamal/elg_op.cpp')
-rw-r--r-- | botan/src/pubkey/elgamal/elg_op.cpp | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/botan/src/pubkey/elgamal/elg_op.cpp b/botan/src/pubkey/elgamal/elg_op.cpp new file mode 100644 index 0000000..1e476ab --- /dev/null +++ b/botan/src/pubkey/elgamal/elg_op.cpp @@ -0,0 +1,56 @@ +/* +* ElGamal Operations +* (C) 1999-2007 Jack Lloyd +* +* Distributed under the terms of the Botan license +*/ + +#include <botan/elg_op.h> + +namespace Botan { + +/* +* Default_ELG_Op Constructor +*/ +Default_ELG_Op::Default_ELG_Op(const DL_Group& group, const BigInt& y, + const BigInt& x) : p(group.get_p()) + { + powermod_g_p = Fixed_Base_Power_Mod(group.get_g(), p); + powermod_y_p = Fixed_Base_Power_Mod(y, p); + mod_p = Modular_Reducer(p); + + if(x != 0) + powermod_x_p = Fixed_Exponent_Power_Mod(x, p); + } + +/* +* Default ElGamal Encrypt Operation +*/ +SecureVector<byte> Default_ELG_Op::encrypt(const byte in[], u32bit length, + const BigInt& k) const + { + BigInt m(in, length); + if(m >= p) + throw Invalid_Argument("Default_ELG_Op::encrypt: Input is too large"); + + BigInt a = powermod_g_p(k); + BigInt b = mod_p.multiply(m, powermod_y_p(k)); + + SecureVector<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; + } + +/* +* Default ElGamal Decrypt Operation +*/ +BigInt Default_ELG_Op::decrypt(const BigInt& a, const BigInt& b) const + { + if(a >= p || b >= p) + throw Invalid_Argument("Default_ELG_Op: Invalid message"); + + return mod_p.multiply(b, inverse_mod(powermod_x_p(a), p)); + } + +} |