trezor-firmware/core/embed/extmod/modtrezorcrypto/modtrezorcrypto-curve25519.h

/*
 * This file is part of the Trezor project, https://trezor.io/
 *
 * Copyright (c) SatoshiLabs
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "py/objstr.h"

#include "ed25519-donna/ed25519.h"

#include "rand.h"

/// package: trezorcrypto.curve25519

/// def generate_secret() -> bytes:
///     """
///     Generate secret key.
///     """
STATIC mp_obj_t mod_trezorcrypto_curve25519_generate_secret() {
  vstr_t sk = {0};
  vstr_init_len(&sk, 32);
  random_buffer((uint8_t *)sk.buf, sk.len);
  // taken from https://cr.yp.to/ecdh.html
  sk.buf[0] &= 248;
  sk.buf[31] &= 127;
  sk.buf[31] |= 64;
  return mp_obj_new_str_from_vstr(&mp_type_bytes, &sk);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_0(
    mod_trezorcrypto_curve25519_generate_secret_obj,
    mod_trezorcrypto_curve25519_generate_secret);

/// def publickey(secret_key: bytes) -> bytes:
///     """
///     Computes public key from secret key.
///     """
STATIC mp_obj_t mod_trezorcrypto_curve25519_publickey(mp_obj_t secret_key) {
  mp_buffer_info_t sk = {0};
  mp_get_buffer_raise(secret_key, &sk, MP_BUFFER_READ);
  if (sk.len != 32) {
    mp_raise_ValueError("Invalid length of secret key");
  }
  vstr_t pk = {0};
  vstr_init_len(&pk, 32);
  curve25519_scalarmult_basepoint((uint8_t *)pk.buf, (const uint8_t *)sk.buf);
  return mp_obj_new_str_from_vstr(&mp_type_bytes, &pk);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_trezorcrypto_curve25519_publickey_obj,
                                 mod_trezorcrypto_curve25519_publickey);

/// def multiply(secret_key: bytes, public_key: bytes) -> bytes:
///     """
///     Multiplies point defined by public_key with scalar defined by
///     secret_key. Useful for ECDH.
///     """
STATIC mp_obj_t mod_trezorcrypto_curve25519_multiply(mp_obj_t secret_key,
                                                     mp_obj_t public_key) {
  mp_buffer_info_t sk = {0}, pk = {0};
  mp_get_buffer_raise(secret_key, &sk, MP_BUFFER_READ);
  mp_get_buffer_raise(public_key, &pk, MP_BUFFER_READ);
  if (sk.len != 32) {
    mp_raise_ValueError("Invalid length of secret key");
  }
  if (pk.len != 32) {
    mp_raise_ValueError("Invalid length of public key");
  }
  vstr_t out = {0};
  vstr_init_len(&out, 32);
  curve25519_scalarmult((uint8_t *)out.buf, (const uint8_t *)sk.buf,
                        (const uint8_t *)pk.buf);
  return mp_obj_new_str_from_vstr(&mp_type_bytes, &out);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorcrypto_curve25519_multiply_obj,
                                 mod_trezorcrypto_curve25519_multiply);

STATIC const mp_rom_map_elem_t mod_trezorcrypto_curve25519_globals_table[] = {
    {MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_curve25519)},
    {MP_ROM_QSTR(MP_QSTR_generate_secret),
     MP_ROM_PTR(&mod_trezorcrypto_curve25519_generate_secret_obj)},
    {MP_ROM_QSTR(MP_QSTR_publickey),
     MP_ROM_PTR(&mod_trezorcrypto_curve25519_publickey_obj)},
    {MP_ROM_QSTR(MP_QSTR_multiply),
     MP_ROM_PTR(&mod_trezorcrypto_curve25519_multiply_obj)},
};
STATIC MP_DEFINE_CONST_DICT(mod_trezorcrypto_curve25519_globals,
                            mod_trezorcrypto_curve25519_globals_table);

STATIC const mp_obj_module_t mod_trezorcrypto_curve25519_module = {
    .base = {&mp_type_module},
    .globals = (mp_obj_dict_t *)&mod_trezorcrypto_curve25519_globals,
};