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/*
* DSA
* (C) 1999-2010 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/dsa.h>
#include <botan/numthry.h>
#include <botan/keypair.h>
#include <botan/look_pk.h>
namespace Botan {
/*
* DSA_PublicKey Constructor
*/
DSA_PublicKey::DSA_PublicKey(const DL_Group& grp, const BigInt& y1)
{
group = grp;
y = y1;
}
/*
* Create a DSA private key
*/
DSA_PrivateKey::DSA_PrivateKey(RandomNumberGenerator& rng,
const DL_Group& grp,
const BigInt& x_arg)
{
group = grp;
x = x_arg;
if(x == 0)
x = BigInt::random_integer(rng, 2, group_q() - 1);
y = power_mod(group_g(), x, group_p());
if(x_arg == 0)
gen_check(rng);
else
load_check(rng);
}
DSA_PrivateKey::DSA_PrivateKey(const AlgorithmIdentifier& alg_id,
const MemoryRegion<byte>& key_bits,
RandomNumberGenerator& rng) :
DL_Scheme_PrivateKey(alg_id, key_bits, DL_Group::ANSI_X9_57)
{
y = power_mod(group_g(), x, group_p());
load_check(rng);
}
/*
* Check Private DSA Parameters
*/
bool DSA_PrivateKey::check_key(RandomNumberGenerator& rng, bool strong) const
{
if(!DL_Scheme_PrivateKey::check_key(rng, strong) || x >= group_q())
return false;
if(!strong)
return true;
try
{
KeyPair::check_key(rng,
get_pk_signer(*this, "EMSA1(SHA-1)"),
get_pk_verifier(*this, "EMSA1(SHA-1)")
);
}
catch(Self_Test_Failure)
{
return false;
}
return true;
}
DSA_Signature_Operation::DSA_Signature_Operation(const DSA_PrivateKey& dsa) :
q(dsa.group_q()),
x(dsa.get_x()),
powermod_g_p(dsa.group_g(), dsa.group_p()),
mod_q(dsa.group_q())
{
}
SecureVector<byte> DSA_Signature_Operation::sign(const byte msg[],
u32bit msg_len,
RandomNumberGenerator& rng)
{
rng.add_entropy(msg, msg_len);
BigInt k;
do
k.randomize(rng, q.bits());
while(k >= q);
BigInt i(msg, msg_len);
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("DSA signature gen failure: 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;
}
DSA_Verification_Operation::DSA_Verification_Operation(const DSA_PublicKey& dsa) :
q(dsa.group_q()), y(dsa.get_y())
{
powermod_g_p = Fixed_Base_Power_Mod(dsa.group_g(), dsa.group_p());
powermod_y_p = Fixed_Base_Power_Mod(y, dsa.group_p());
mod_p = Modular_Reducer(dsa.group_p());
mod_q = Modular_Reducer(dsa.group_q());
}
bool DSA_Verification_Operation::verify(const byte msg[], u32bit msg_len,
const byte sig[], u32bit sig_len)
{
const BigInt& q = mod_q.get_modulus();
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);
}
}
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