tdlight/td/mtproto/DhHandshake.cpp
2021-07-05 21:20:07 +03:00

233 lines
6.0 KiB
C++

//
// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2021
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#include "td/mtproto/DhHandshake.h"
#include "td/mtproto/DhCallback.h"
#include "td/utils/as.h"
#include "td/utils/crypto.h"
#include "td/utils/logging.h"
#include "td/utils/Slice.h"
#include "td/utils/Status.h"
#include "td/utils/UInt.h"
namespace td {
namespace mtproto {
Status DhHandshake::check_config(Slice prime_str, const BigNum &prime, int32 g_int, BigNumContext &ctx,
DhCallback *callback) {
// check that 2^2047 <= p < 2^2048
if (prime.get_num_bits() != 2048) {
return Status::Error("p is not 2048-bit number");
}
// g generates a cyclic subgroup of prime order (p - 1) / 2, i.e. is a quadratic residue mod p.
// Since g is always equal to 2, 3, 4, 5, 6 or 7, this is easily done using quadratic reciprocity law,
// yielding a simple condition on
// * p mod 4g - namely, p mod 8 = 7 for g = 2; p mod 3 = 2 for g = 3;
// * no extra condition for g = 4;
// * p mod 5 = 1 or 4 for g = 5;
// * p mod 24 = 19 or 23 for g = 6;
// * p mod 7 = 3, 5 or 6 for g = 7.
bool mod_ok;
uint32 mod_r;
switch (g_int) {
case 2:
mod_ok = prime % 8 == 7u;
break;
case 3:
mod_ok = prime % 3 == 2u;
break;
case 4:
mod_ok = true;
break;
case 5:
mod_ok = (mod_r = prime % 5) == 1u || mod_r == 4u;
break;
case 6:
mod_ok = (mod_r = prime % 24) == 19u || mod_r == 23u;
break;
case 7:
mod_ok = (mod_r = prime % 7) == 3u || mod_r == 5u || mod_r == 6u;
break;
default:
mod_ok = false;
}
if (!mod_ok) {
return Status::Error("Bad prime mod 4g");
}
// check whether p is a safe prime (meaning that both p and (p - 1) / 2 are prime)
int is_good_prime = -1;
if (callback) {
is_good_prime = callback->is_good_prime(prime_str);
}
if (is_good_prime != -1) {
return is_good_prime ? Status::OK() : Status::Error("p or (p - 1) / 2 is not a prime number");
}
if (!prime.is_prime(ctx)) {
if (callback) {
callback->add_bad_prime(prime_str);
}
return Status::Error("p is not a prime number");
}
BigNum half_prime = prime;
half_prime -= 1;
half_prime /= 2;
if (!half_prime.is_prime(ctx)) {
if (callback) {
callback->add_bad_prime(prime_str);
}
return Status::Error("(p - 1) / 2 is not a prime number");
}
if (callback) {
callback->add_good_prime(prime_str);
}
return Status::OK();
}
Status DhHandshake::dh_check(const BigNum &prime, const BigNum &g_a, const BigNum &g_b) {
// IMPORTANT: Apart from the conditions on the Diffie-Hellman prime dh_prime and generator g, both sides are
// to check that g, g_a and g_b are greater than 1 and less than dh_prime - 1.
// We recommend checking that g_a and g_b are between 2^{2048-64} and dh_prime - 2^{2048-64} as well.
CHECK(prime.get_num_bits() == 2048);
BigNum left;
left.set_value(0);
left.set_bit(2048 - 64);
BigNum right;
BigNum::sub(right, prime, left);
if (BigNum::compare(left, g_a) > 0 || BigNum::compare(g_a, right) > 0 || BigNum::compare(left, g_b) > 0 ||
BigNum::compare(g_b, right) > 0) {
std::string x(2048, '0');
std::string y(2048, '0');
for (int i = 0; i < 2048; i++) {
if (g_a.is_bit_set(i)) {
x[i] = '1';
}
if (g_b.is_bit_set(i)) {
y[i] = '1';
}
}
LOG(ERROR) << x;
LOG(ERROR) << y;
return Status::Error("g^a or g^b is not between 2^{2048-64} and dh_prime - 2^{2048-64}");
}
return Status::OK();
}
void DhHandshake::set_config(int32 g_int, Slice prime_str) {
has_config_ = true;
prime_ = BigNum::from_binary(prime_str);
prime_str_ = prime_str.str();
b_ = BigNum();
g_b_ = BigNum();
BigNum::random(b_, 2048, -1, 0);
// g^b
g_int_ = g_int;
g_.set_value(g_int_);
BigNum::mod_exp(g_b_, g_, b_, prime_, ctx_);
}
Status DhHandshake::check_config(int32 g_int, Slice prime_str, DhCallback *callback) {
BigNumContext ctx;
auto prime = BigNum::from_binary(prime_str);
return check_config(prime_str, prime, g_int, ctx, callback);
}
void DhHandshake::set_g_a_hash(Slice g_a_hash) {
has_g_a_hash_ = true;
ok_g_a_hash_ = false;
CHECK(!has_g_a_);
g_a_hash_ = g_a_hash.str();
}
void DhHandshake::set_g_a(Slice g_a_str) {
has_g_a_ = true;
if (has_g_a_hash_) {
string g_a_hash(32, ' ');
sha256(g_a_str, g_a_hash);
ok_g_a_hash_ = g_a_hash == g_a_hash_;
}
g_a_ = BigNum::from_binary(g_a_str);
}
string DhHandshake::get_g_a() const {
CHECK(has_g_a_);
return g_a_.to_binary();
}
string DhHandshake::get_g_b() const {
CHECK(has_config_);
return g_b_.to_binary();
}
string DhHandshake::get_g_b_hash() const {
string g_b_hash(32, ' ');
sha256(get_g_b(), g_b_hash);
return g_b_hash;
}
Status DhHandshake::run_checks(bool skip_config_check, DhCallback *callback) {
CHECK(has_g_a_ && has_config_);
if (has_g_a_hash_ && !ok_g_a_hash_) {
return Status::Error("g_a_hash mismatch");
}
if (!skip_config_check) {
TRY_STATUS(check_config(prime_str_, prime_, g_int_, ctx_, callback));
}
return dh_check(prime_, g_a_, g_b_);
}
BigNum DhHandshake::get_g() const {
CHECK(has_config_);
return g_;
}
BigNum DhHandshake::get_p() const {
CHECK(has_config_);
return prime_;
}
BigNum DhHandshake::get_b() const {
CHECK(has_config_);
return b_;
}
BigNum DhHandshake::get_g_ab() {
CHECK(has_g_a_ && has_config_);
BigNum g_ab;
BigNum::mod_exp(g_ab, g_a_, b_, prime_, ctx_);
return g_ab;
}
std::pair<int64, string> DhHandshake::gen_key() {
string key = get_g_ab().to_binary(2048 / 8);
auto key_id = calc_key_id(key);
return std::pair<int64, string>(key_id, std::move(key));
}
int64 DhHandshake::calc_key_id(Slice auth_key) {
UInt<160> auth_key_sha1;
sha1(auth_key, auth_key_sha1.raw);
return as<int64>(auth_key_sha1.raw + 12);
}
} // namespace mtproto
} // namespace td