trezor-firmware/embed/extmod/modtrezorcrypto/modtrezorcrypto-secp256k1.h

/*
 * Copyright (c) Pavol Rusnak, SatoshiLabs
 *
 * Licensed under TREZOR License
 * see LICENSE file for details
 */

#include "py/objstr.h"

#include "ecdsa.h"
#include "secp256k1.h"

/// def generate_secret() -> bytes:
///     '''
///     Generate secret key.
///     '''
STATIC mp_obj_t mod_trezorcrypto_secp256k1_generate_secret() {
    vstr_t vstr;
    vstr_init_len(&vstr, 32);
    for (;;) {
        random_buffer((uint8_t *)vstr.buf, 32);
        // check whether secret > 0 && secret < curve_order
        if (0 == memcmp(vstr.buf, "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", 32)) continue;
        if (0 <= memcmp(vstr.buf, "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFE\xBA\xAE\xDC\xE6\xAF\x48\xA0\x3B\xBF\xD2\x5E\x8C\xD0\x36\x41\x41", 32)) continue;
        break;
    }
    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_0(mod_trezorcrypto_secp256k1_generate_secret_obj, mod_trezorcrypto_secp256k1_generate_secret);

/// def publickey(secret_key: bytes, compressed: bool = True) -> bytes:
///     '''
///     Computes public key from secret key.
///     '''
STATIC mp_obj_t mod_trezorcrypto_secp256k1_publickey(size_t n_args, const mp_obj_t *args) {
    mp_buffer_info_t sk;
    mp_get_buffer_raise(args[0], &sk, MP_BUFFER_READ);
    if (sk.len != 32) {
        mp_raise_ValueError("Invalid length of secret key");
    }
    bool compressed = n_args < 2 || args[1] == mp_const_true;
    vstr_t vstr;
    if (compressed) {
        vstr_init_len(&vstr, 33);
        ecdsa_get_public_key33(&secp256k1, (const uint8_t *)sk.buf, (uint8_t *)vstr.buf);
    } else {
        vstr_init_len(&vstr, 65);
        ecdsa_get_public_key65(&secp256k1, (const uint8_t *)sk.buf, (uint8_t *)vstr.buf);
    }
    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorcrypto_secp256k1_publickey_obj, 1, 2, mod_trezorcrypto_secp256k1_publickey);

/// def sign(secret_key: bytes, digest: bytes, compressed: bool = True) -> bytes:
///     '''
///     Uses secret key to produce the signature of the digest.
///     '''
STATIC mp_obj_t mod_trezorcrypto_secp256k1_sign(size_t n_args, const mp_obj_t *args) {
    mp_buffer_info_t sk, dig;
    mp_get_buffer_raise(args[0], &sk, MP_BUFFER_READ);
    mp_get_buffer_raise(args[1], &dig, MP_BUFFER_READ);
    bool compressed = n_args < 3 || args[2] == mp_const_true;
    if (sk.len != 32) {
        mp_raise_ValueError("Invalid length of secret key");
    }
    if (dig.len != 32) {
        mp_raise_ValueError("Invalid length of digest");
    }
    vstr_t vstr;
    vstr_init_len(&vstr, 65);
    uint8_t pby;
    if (0 != ecdsa_sign_digest(&secp256k1, (const uint8_t *)sk.buf, (const uint8_t *)dig.buf, (uint8_t *)vstr.buf + 1, &pby, NULL)) {
        mp_raise_ValueError("Signing failed");
    }
    vstr.buf[0] = 27 + pby + compressed * 4;
    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorcrypto_secp256k1_sign_obj, 2, 3, mod_trezorcrypto_secp256k1_sign);

/// def verify(public_key: bytes, signature: bytes, digest: bytes) -> bool:
///     '''
///     Uses public key to verify the signature of the digest.
///     Returns True on success.
///     '''
STATIC mp_obj_t mod_trezorcrypto_secp256k1_verify(mp_obj_t public_key, mp_obj_t signature, mp_obj_t digest) {
    mp_buffer_info_t pk, sig, dig;
    mp_get_buffer_raise(public_key, &pk, MP_BUFFER_READ);
    mp_get_buffer_raise(signature, &sig, MP_BUFFER_READ);
    mp_get_buffer_raise(digest, &dig, MP_BUFFER_READ);
    if (pk.len != 33 && pk.len != 65) {
        mp_raise_ValueError("Invalid length of public key");
    }
    if (sig.len != 64 && sig.len != 65) {
        mp_raise_ValueError("Invalid length of signature");
    }
    int offset = sig.len - 64;
    if (dig.len != 32) {
        mp_raise_ValueError("Invalid length of digest");
    }
    return mp_obj_new_bool(0 == ecdsa_verify_digest(&secp256k1, (const uint8_t *)pk.buf, (const uint8_t *)sig.buf + offset, (const uint8_t *)dig.buf));
}
STATIC MP_DEFINE_CONST_FUN_OBJ_3(mod_trezorcrypto_secp256k1_verify_obj, mod_trezorcrypto_secp256k1_verify);

/// def verify_recover(signature: bytes, digest: bytes) -> bytes:
///     '''
///     Uses signature of the digest to verify the digest and recover the public key.
///     Returns public key on success, None on failure.
///     '''
STATIC mp_obj_t mod_trezorcrypto_secp256k1_verify_recover(mp_obj_t signature, mp_obj_t digest) {
    mp_buffer_info_t sig, dig;
    mp_get_buffer_raise(signature, &sig, MP_BUFFER_READ);
    mp_get_buffer_raise(digest, &dig, MP_BUFFER_READ);
    if (sig.len != 65) {
        mp_raise_ValueError("Invalid length of signature");
    }
    if (dig.len != 32) {
        mp_raise_ValueError("Invalid length of digest");
    }
    uint8_t recid = ((const uint8_t *)sig.buf)[0] - 27;
    if (recid >= 8) {
        mp_raise_ValueError("Invalid recid in signature");
    }
    bool compressed = (recid >= 4);
    recid &= 3;
    vstr_t vstr;
    vstr_init_len(&vstr, 65);
    if (0 == ecdsa_verify_digest_recover(&secp256k1, (uint8_t *)vstr.buf, (const uint8_t *)sig.buf + 1, (const uint8_t *)dig.buf, recid)) {
        if (compressed) {
            vstr.buf[0] = 0x02 | (vstr.buf[64] & 1);
            vstr.len = 33;
        }
        return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
    } else {
        return mp_const_none;
    }
}
STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorcrypto_secp256k1_verify_recover_obj, mod_trezorcrypto_secp256k1_verify_recover);

/// 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_secp256k1_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 != 33 && pk.len != 65) {
        mp_raise_ValueError("Invalid length of public key");
    }
    vstr_t vstr;
    vstr_init_len(&vstr, 65);
    if (0 != ecdh_multiply(&secp256k1, (const uint8_t *)sk.buf, (const uint8_t *)pk.buf, (uint8_t *)vstr.buf)) {
        mp_raise_ValueError("Multiply failed");
    }
    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorcrypto_secp256k1_multiply_obj, mod_trezorcrypto_secp256k1_multiply);

STATIC const mp_rom_map_elem_t mod_trezorcrypto_secp256k1_globals_table[] = {
    { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_secp256k1) },
    { MP_ROM_QSTR(MP_QSTR_generate_secret), MP_ROM_PTR(&mod_trezorcrypto_secp256k1_generate_secret_obj) },
    { MP_ROM_QSTR(MP_QSTR_publickey), MP_ROM_PTR(&mod_trezorcrypto_secp256k1_publickey_obj) },
    { MP_ROM_QSTR(MP_QSTR_sign), MP_ROM_PTR(&mod_trezorcrypto_secp256k1_sign_obj) },
    { MP_ROM_QSTR(MP_QSTR_verify), MP_ROM_PTR(&mod_trezorcrypto_secp256k1_verify_obj) },
    { MP_ROM_QSTR(MP_QSTR_verify_recover), MP_ROM_PTR(&mod_trezorcrypto_secp256k1_verify_recover_obj) },
    { MP_ROM_QSTR(MP_QSTR_multiply), MP_ROM_PTR(&mod_trezorcrypto_secp256k1_multiply_obj) },
};
STATIC MP_DEFINE_CONST_DICT(mod_trezorcrypto_secp256k1_globals, mod_trezorcrypto_secp256k1_globals_table);

STATIC const mp_obj_module_t mod_trezorcrypto_secp256k1_module = {
    .base = { &mp_type_module },
    .globals = (mp_obj_dict_t*)&mod_trezorcrypto_secp256k1_globals,
};