trezor-firmware/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"

/// def generate_secret() -> bytes:
///     '''
///     Generate secret key.
///     '''
STATIC mp_obj_t mod_trezorcrypto_curve25519_generate_secret() {
    uint8_t out[32];
    random_buffer(out, 32);
    // taken from https://cr.yp.to/ecdh.html
    out[0] &= 248;
    out[31] &= 127;
    out[31] |= 64;
    return mp_obj_new_bytes(out, sizeof(out));
}
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;
    mp_get_buffer_raise(secret_key, &sk, MP_BUFFER_READ);
    if (sk.len != 32) {
        mp_raise_ValueError("Invalid length of secret key");
    }
    uint8_t out[32];
    curve25519_scalarmult_basepoint(out, (const uint8_t *)sk.buf);
    return mp_obj_new_bytes(out, sizeof(out));
}
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, pk;
    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");
    }
    uint8_t out[32];
    curve25519_scalarmult(out, (const uint8_t *)sk.buf, (const uint8_t *)pk.buf);
    return mp_obj_new_bytes(out, sizeof(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,
};