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/*
* SRP-6a
* (C) 2011 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/srp6.h>
#include <botan/dl_group.h>
#include <botan/libstate.h>
#include <botan/numthry.h>
#include <memory>
namespace Botan {
namespace {
BigInt hash_seq(const std::string& hash_id,
size_t pad_to,
const BigInt& in1,
const BigInt& in2)
{
std::auto_ptr<HashFunction> hash_fn(
global_state().algorithm_factory().make_hash_function(hash_id));
hash_fn->update(BigInt::encode_1363(in1, pad_to));
hash_fn->update(BigInt::encode_1363(in2, pad_to));
return BigInt::decode(hash_fn->final());
}
BigInt hash_seq(const std::string& hash_id,
size_t pad_to,
const BigInt& in1,
const BigInt& in2,
const BigInt& in3)
{
std::auto_ptr<HashFunction> hash_fn(
global_state().algorithm_factory().make_hash_function(hash_id));
hash_fn->update(BigInt::encode_1363(in1, pad_to));
hash_fn->update(BigInt::encode_1363(in2, pad_to));
hash_fn->update(BigInt::encode_1363(in3, pad_to));
return BigInt::decode(hash_fn->final());
}
BigInt compute_x(const std::string& hash_id,
const std::string& identifier,
const std::string& password,
const MemoryRegion<byte>& salt)
{
std::auto_ptr<HashFunction> hash_fn(
global_state().algorithm_factory().make_hash_function(hash_id));
hash_fn->update(identifier);
hash_fn->update(":");
hash_fn->update(password);
SecureVector<byte> inner_h = hash_fn->final();
hash_fn->update(salt);
hash_fn->update(inner_h);
SecureVector<byte> outer_h = hash_fn->final();
return BigInt::decode(outer_h);
}
}
std::pair<BigInt, SymmetricKey>
SRP6_Client_Session:: step1(const std::string& identifier,
const std::string& password,
const std::string& group_id,
const std::string& hash_id,
const MemoryRegion<byte>& salt,
const BigInt& B,
RandomNumberGenerator& rng)
{
DL_Group group(group_id);
const BigInt& g = group.get_g();
const BigInt& p = group.get_p();
const size_t p_bytes = group.get_p().bytes();
if(B % p == 0)
throw std::runtime_error("Invalid SRP parameter from server");
BigInt k = hash_seq(hash_id, p_bytes, p, g);
BigInt a(rng, p.bits() - 1);
BigInt A = power_mod(g, a, p);
BigInt u = hash_seq(hash_id, p_bytes, A, B);
const BigInt x = compute_x(hash_id, identifier, password, salt);
BigInt S = power_mod((B - (k * power_mod(g, x, p))) % p, (a + (u * x)), p);
SymmetricKey Sk(BigInt::encode_1363(S, p_bytes));
return std::make_pair(A, Sk);
}
BigInt SRP6_Client_Session::generate_verifier(const std::string& identifier,
const std::string& password,
const MemoryRegion<byte>& salt,
const std::string& group_id,
const std::string& hash_id)
{
const BigInt x = compute_x(hash_id, identifier, password, salt);
DL_Group group(group_id);
return power_mod(group.get_g(), x, group.get_p());
}
BigInt SRP6_Server_Session::step1(const BigInt& v,
const std::string& group_id,
const std::string& hash_id,
RandomNumberGenerator& rng)
{
DL_Group group(group_id);
const BigInt& g = group.get_g();
const BigInt& p = group.get_p();
p_bytes = p.bytes();
BigInt k = hash_seq(hash_id, p_bytes, p, g);
BigInt b(rng, p.bits() - 1);
B = (v*k + power_mod(g, b, p)) % p;
this->v = v;
this->b = b;
this->p = p;
this->hash_id = hash_id;
return B;
}
SymmetricKey SRP6_Server_Session::step2(const BigInt& A)
{
if(A % p == 0)
throw std::runtime_error("Invalid SRP parameter from client");
BigInt u = hash_seq(hash_id, p_bytes, A, B);
BigInt S = power_mod(A * power_mod(v, u, p), b, p);
return BigInt::encode_1363(S, p_bytes);
}
}
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