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/*************************************************
* DSA 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 DSA Operation *
*************************************************/
class Default_DSA_Op : public DSA_Operation
{
public:
bool verify(const byte[], u32bit, const byte[], u32bit) const;
SecureVector<byte> sign(const byte[], u32bit, const BigInt&) const;
DSA_Operation* clone() const { return new Default_DSA_Op(*this); }
Default_DSA_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_DSA_Op Constructor *
*************************************************/
Default_DSA_Op::Default_DSA_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 DSA Verify Operation *
*************************************************/
bool Default_DSA_Op::verify(const byte msg[], u32bit msg_len,
const byte sig[], u32bit sig_len) const
{
const BigInt& q = group.get_q();
if(sig_len != 2*q.bytes() || msg_len > q.bytes())
return false;
BigInt r(sig, q.bytes());
BigInt s(sig + q.bytes(), q.bytes());
BigInt i(msg, msg_len);
if(r <= 0 || r >= q || s <= 0 || s >= q)
return false;
s = inverse_mod(s, q);
s = mod_p.multiply(powermod_g_p(mod_q.multiply(s, i)),
powermod_y_p(mod_q.multiply(s, r)));
return (mod_q.reduce(s) == r);
}
/*************************************************
* Default DSA Sign Operation *
*************************************************/
SecureVector<byte> Default_DSA_Op::sign(const byte in[], u32bit length,
const BigInt& k) const
{
if(x == 0)
throw Internal_Error("Default_DSA_Op::sign: No private key");
const BigInt& q = group.get_q();
BigInt i(in, length);
BigInt r = mod_q.reduce(powermod_g_p(k));
BigInt s = mod_q.multiply(inverse_mod(k, q), mul_add(x, r, i));
if(r.is_zero() || s.is_zero())
throw Internal_Error("Default_DSA_Op::sign: r or s was zero");
SecureVector<byte> output(2*q.bytes());
r.binary_encode(output + (output.size() / 2 - r.bytes()));
s.binary_encode(output + (output.size() - s.bytes()));
return output;
}
}
/*************************************************
* Acquire a DSA op *
*************************************************/
DSA_Operation* Default_Engine::dsa_op(const DL_Group& group, const BigInt& y,
const BigInt& x) const
{
return new Default_DSA_Op(group, y, x);
}
}
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