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/*************************************************
* NR Operations Source File *
* (C) 1999-2007 Jack Lloyd *
*************************************************/
#include <botan/eng_def.h>
#include <botan/pow_mod.h>
#include <botan/numthry.h>
#include <botan/reducer.h>
namespace Botan {
namespace {
/*************************************************
* Default NR Operation *
*************************************************/
class Default_NR_Op : public NR_Operation
{
public:
SecureVector<byte> verify(const byte[], u32bit) const;
SecureVector<byte> sign(const byte[], u32bit, const BigInt&) const;
NR_Operation* clone() const { return new Default_NR_Op(*this); }
Default_NR_Op(const DL_Group&, const BigInt&, const BigInt&);
private:
const BigInt x, y;
const DL_Group group;
Fixed_Base_Power_Mod powermod_g_p, powermod_y_p;
Modular_Reducer mod_p, mod_q;
};
/*************************************************
* Default_NR_Op Constructor *
*************************************************/
Default_NR_Op::Default_NR_Op(const DL_Group& grp, const BigInt& y1,
const BigInt& x1) : x(x1), y(y1), group(grp)
{
powermod_g_p = Fixed_Base_Power_Mod(group.get_g(), group.get_p());
powermod_y_p = Fixed_Base_Power_Mod(y, group.get_p());
mod_p = Modular_Reducer(group.get_p());
mod_q = Modular_Reducer(group.get_q());
}
/*************************************************
* Default NR Verify Operation *
*************************************************/
SecureVector<byte> Default_NR_Op::verify(const byte in[], u32bit length) const
{
const BigInt& q = group.get_q();
if(length != 2*q.bytes())
return false;
BigInt c(in, q.bytes());
BigInt d(in + q.bytes(), q.bytes());
if(c.is_zero() || c >= q || d >= q)
throw Invalid_Argument("Default_NR_Op::verify: Invalid signature");
BigInt i = mod_p.multiply(powermod_g_p(d), powermod_y_p(c));
return BigInt::encode(mod_q.reduce(c - i));
}
/*************************************************
* Default NR Sign Operation *
*************************************************/
SecureVector<byte> Default_NR_Op::sign(const byte in[], u32bit length,
const BigInt& k) const
{
if(x == 0)
throw Internal_Error("Default_NR_Op::sign: No private key");
const BigInt& q = group.get_q();
BigInt f(in, length);
if(f >= q)
throw Invalid_Argument("Default_NR_Op::sign: Input is out of range");
BigInt c = mod_q.reduce(powermod_g_p(k) + f);
if(c.is_zero())
throw Internal_Error("Default_NR_Op::sign: c was zero");
BigInt d = mod_q.reduce(k - x * c);
SecureVector<byte> output(2*q.bytes());
c.binary_encode(output + (output.size() / 2 - c.bytes()));
d.binary_encode(output + (output.size() - d.bytes()));
return output;
}
}
/*************************************************
* Acquire a NR op *
*************************************************/
NR_Operation* Default_Engine::nr_op(const DL_Group& group, const BigInt& y,
const BigInt& x) const
{
return new Default_NR_Op(group, y, x);
}
}
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