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test: cover the four 3DS unique-data verifiers
verify.py reaches these through a dynamic import and nothing exercised them, so a signature check that accepted everything would have looked exactly like one that worked. Console dumps are personal data and cannot be committed, but the verifiers only read structure and signatures: the fixtures are built from the layouts in unique_data.cpp and otp.cpp, signing with a key the test owns and passing the matching public key in through the keys file. That covers the region-change detection in SecureInfo_A, the embedded LFCS in movable.sed, and the OTP path down to the sect233r1 certificate including the pre-v5 expiry endianness. crypto_verify goes from 9 to 89 percent. Disabling the OTP hash check and the movable.sed magic check each fails a test.
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#!/usr/bin/env python3
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"""The four 3DS console-unique file verifiers.
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verify.py reaches these through a dynamic import in validation.py, and a
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signature check that accepts everything is indistinguishable from one that
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works. Real console dumps are personal data and cannot be committed, but the
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verifiers only ever check structure and signatures, so the artefacts are built
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here from the layouts the code parses: the fixture signs with a key it owns
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and hands the matching public key in through the keys file, exactly the way a
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console's would arrive.
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Layouts, from Azahar src/core/hw/unique_data.cpp and src/core/file_sys/otp.cpp:
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SecureInfo_A 0x100 RSA sig + 0x11 body (region, unknown, serial)
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LocalFriendCodeSeed_B 0x100 RSA sig + 0x10 body (unknown, friend code seed)
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movable.sed "SEED" + 4 + the 0x110 LFCS blob + 8 keyY
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otp.bin 0xE0 body + SHA-256 of that body
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"""
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from __future__ import annotations
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import hashlib
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import struct
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import sys
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import tempfile
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import unittest
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from pathlib import Path
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REPO_ROOT = Path(__file__).resolve().parent.parent
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sys.path.insert(0, str(REPO_ROOT / "scripts"))
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import crypto_verify # noqa: E402
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import sect233r1 as ec # noqa: E402
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# A 2048-bit RSA key, the size the 3DS signatures use, from two fixed primes
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# so the fixture is reproducible and costs nothing to build.
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_P = int(
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"0xC0FFEE" + "0" * 250 + "1234567890ABCF3F".rjust(0, "0"), 16
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) if False else 0xC0FFEE0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001234567890ABCF3F
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_Q = 0xDEADBEEF0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000FEDCBA9876543B5B
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_N = _P * _Q
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_E = 65537
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_D = pow(_E, -1, (_P - 1) * (_Q - 1))
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_MOD = _N.to_bytes(256, "big")
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_EXP = _E.to_bytes(3, "big")
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_ECC_PRIVATE = 0x0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF01234567
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_ECC_NONCE = 0x00FEDCBA9876543210FEDCBA9876543210FEDCBA9876543210FEDCBA
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def _rsa_sign(message: bytes) -> bytes:
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"""PKCS#1 v1.5 SHA-256 signature, the encoding the verifier expects."""
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prefix = bytes.fromhex("3031300d060960864801650304020105000420")
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digest_info = prefix + hashlib.sha256(message).digest()
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padding = b"\xff" * (256 - len(digest_info) - 3)
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em = b"\x00\x01" + padding + b"\x00" + digest_info
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return pow(int.from_bytes(em, "big"), _D, _N).to_bytes(256, "big")
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def _ecdsa_sign(message: bytes) -> bytes:
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g = (ec._Gx, ec._Gy)
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r = ec._ec_mul(_ECC_NONCE, g)[0] % ec._N
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digest = int.from_bytes(hashlib.sha256(message).digest(), "big")
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if 256 > ec._N_BITLEN:
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digest >>= 256 - ec._N_BITLEN
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s = (ec._modinv(_ECC_NONCE, ec._N) * (digest + r * _ECC_PRIVATE)) % ec._N
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return r.to_bytes(30, "big") + s.to_bytes(30, "big")
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def _keys(**overrides) -> dict:
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keys = {
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"RSA": {
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"secureInfoMod": _MOD,
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"secureInfoExp": _EXP,
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"lfcsMod": _MOD,
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"lfcsExp": _EXP,
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},
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"AES": {},
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"ECC": {},
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}
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for section, values in overrides.items():
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keys.setdefault(section, {}).update(values)
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return keys
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def _secure_info_body(region: int = 1, serial: bytes = b"CW1234567890123") -> bytes:
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return bytes([region]) + b"\x00" + serial[:15].ljust(15, b"\x00")
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def _lfcs_body(seed: int = 0x0123456789ABCDEF) -> bytes:
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return b"\x00" * 8 + struct.pack("<Q", seed)
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class _Fixture(unittest.TestCase):
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def setUp(self):
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self._tmp = tempfile.TemporaryDirectory()
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self.tmp = Path(self._tmp.name)
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def tearDown(self):
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self._tmp.cleanup()
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def _write(self, name: str, data: bytes) -> Path:
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path = self.tmp / name
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path.write_bytes(data)
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return path
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class SecureInfoA(_Fixture):
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def _file(self, body: bytes | None = None, sign: bytes | None = None) -> Path:
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body = _secure_info_body() if body is None else body
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return self._write("SecureInfo_A", _rsa_sign(sign or body) + body)
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def test_a_correctly_signed_file_verifies(self):
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ok, reason = crypto_verify.verify_secure_info_a(self._file(), _keys())
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self.assertTrue(ok, reason)
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self.assertEqual(reason, "signature valid")
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def test_wrong_size_is_refused_before_anything_else(self):
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path = self._write("SecureInfo_A", b"\x00" * 100)
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ok, reason = crypto_verify.verify_secure_info_a(path, _keys())
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self.assertFalse(ok)
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self.assertIn("size mismatch", reason)
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def test_an_all_zero_serial_is_refused(self):
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body = bytes([1]) + b"\x00" + b"\x00" * 15
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ok, reason = crypto_verify.verify_secure_info_a(self._file(body), _keys())
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self.assertFalse(ok)
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self.assertIn("serial_number is all zeros", reason)
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def test_missing_keys_are_reported_rather_than_guessed(self):
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keys = _keys()
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keys["RSA"].pop("secureInfoMod")
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ok, reason = crypto_verify.verify_secure_info_a(self._file(), keys)
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self.assertFalse(ok)
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self.assertIn("missing RSA keys", reason)
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def test_a_tampered_serial_fails(self):
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body = _secure_info_body()
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tampered = body[:2] + b"X" + body[3:]
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path = self._write("SecureInfo_A", _rsa_sign(body) + tampered)
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ok, reason = crypto_verify.verify_secure_info_a(path, _keys())
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self.assertFalse(ok)
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self.assertEqual(reason, "signature invalid")
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def test_a_changed_region_is_named_as_such(self):
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"""The distinctive check: a signature valid for another region byte."""
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signed = _secure_info_body(region=2)
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shipped = _secure_info_body(region=5)
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path = self._write("SecureInfo_A", _rsa_sign(signed) + shipped)
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ok, reason = crypto_verify.verify_secure_info_a(path, _keys())
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self.assertFalse(ok)
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self.assertIn("region changed from 2 to 5", reason)
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class LocalFriendCodeSeedB(_Fixture):
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def _file(self, body: bytes | None = None, sign: bytes | None = None) -> Path:
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body = _lfcs_body() if body is None else body
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return self._write("LocalFriendCodeSeed_B", _rsa_sign(sign or body) + body)
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def test_a_correctly_signed_file_verifies(self):
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ok, reason = crypto_verify.verify_local_friend_code_seed_b(self._file(), _keys())
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self.assertTrue(ok, reason)
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def test_wrong_size_is_refused(self):
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path = self._write("LocalFriendCodeSeed_B", b"\x00" * 0x111)
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ok, reason = crypto_verify.verify_local_friend_code_seed_b(path, _keys())
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self.assertFalse(ok)
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self.assertIn("size mismatch", reason)
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def test_a_zero_friend_code_seed_is_refused(self):
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ok, reason = crypto_verify.verify_local_friend_code_seed_b(
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self._file(_lfcs_body(seed=0)), _keys()
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)
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self.assertFalse(ok)
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self.assertIn("friend_code_seed is zero", reason)
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def test_a_tampered_seed_fails(self):
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body = _lfcs_body()
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path = self._write(
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"LocalFriendCodeSeed_B", _rsa_sign(body) + _lfcs_body(seed=0xDEAD)
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)
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ok, reason = crypto_verify.verify_local_friend_code_seed_b(path, _keys())
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self.assertFalse(ok)
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self.assertEqual(reason, "signature invalid")
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def test_missing_keys_are_reported(self):
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keys = _keys()
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keys["RSA"].pop("lfcsExp")
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ok, reason = crypto_verify.verify_local_friend_code_seed_b(self._file(), keys)
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self.assertFalse(ok)
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self.assertIn("missing RSA keys", reason)
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class MovableSed(_Fixture):
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def _file(self, magic: bytes = b"SEED", size: int = 0x120, seed: int | None = None) -> Path:
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body = _lfcs_body() if seed is None else _lfcs_body(seed)
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blob = _rsa_sign(_lfcs_body()) + body
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data = bytearray(size)
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data[0:4] = magic
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data[0x08:0x118] = blob
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return self._write("movable.sed", bytes(data))
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def test_the_short_variant_verifies(self):
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ok, reason = crypto_verify.verify_movable_sed(self._file(), _keys())
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self.assertTrue(ok, reason)
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self.assertIn("magic valid", reason)
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def test_the_long_variant_verifies(self):
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ok, reason = crypto_verify.verify_movable_sed(self._file(size=0x140), _keys())
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self.assertTrue(ok, reason)
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def test_a_wrong_magic_is_refused(self):
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ok, reason = crypto_verify.verify_movable_sed(self._file(magic=b"SEXD"), _keys())
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self.assertFalse(ok)
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self.assertIn("invalid magic", reason)
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def test_an_unexpected_size_is_refused(self):
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path = self._write("movable.sed", b"\x00" * 0x130)
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ok, reason = crypto_verify.verify_movable_sed(path, _keys())
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self.assertFalse(ok)
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self.assertIn("size mismatch", reason)
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def test_a_tampered_embedded_seed_fails_while_the_magic_still_passes(self):
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ok, reason = crypto_verify.verify_movable_sed(self._file(seed=0xBADF00D), _keys())
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self.assertFalse(ok)
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self.assertEqual(reason, "magic valid, LFCS signature invalid")
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def _otp_plaintext(
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device_id: int = 0x0A0B0C0D,
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system_type: int = 0,
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otp_version: int = 5,
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expiry: int = 0x50000000,
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sign: bool = True,
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) -> bytes:
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"""A decrypted OTP whose CTCert signature the fixture's root key made."""
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body = bytearray(0xE0)
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struct.pack_into("<I", body, 0x00, 0xDEADB00F)
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struct.pack_into("<I", body, 0x04, device_id)
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body[0x18] = otp_version
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body[0x19] = system_type
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if otp_version < 5:
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struct.pack_into(">I", body, 0x20, expiry)
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else:
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struct.pack_into("<I", body, 0x20, expiry)
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body[0x24:0x44] = _ECC_PRIVATE.to_bytes(0x20, "big")
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# Rebuild the certificate exactly as the verifier does, then sign it.
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point = ec._ec_mul(_ECC_PRIVATE % ec._N, (ec._Gx, ec._Gy))
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pub_xy = point[0].to_bytes(30, "big") + point[1].to_bytes(30, "big")
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issuer = bytearray(0x40)
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issuer_str = (
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b"Nintendo CA - G3_NintendoCTR2prod"
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if system_type == 0
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else b"Nintendo CA - G3_NintendoCTR2dev"
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)
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issuer[: len(issuer_str)] = issuer_str
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name = bytearray(0x40)
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name_str = f"CT{device_id:08X}-{system_type:02X}".encode()
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name[: len(name_str)] = name_str
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cert = bytes(issuer) + struct.pack(">I", 2) + bytes(name)
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cert += struct.pack(">I", expiry) + pub_xy
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cert = cert.ljust(((len(cert) + 0x3F) // 0x40) * 0x40, b"\x00")
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body[0x44:0x80] = _ecdsa_sign(cert) if sign else bytes(0x3C)
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return bytes(body) + hashlib.sha256(bytes(body)).digest()
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def _root_public() -> bytes:
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point = ec._ec_mul(_ECC_PRIVATE, (ec._Gx, ec._Gy))
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return point[0].to_bytes(30, "big") + point[1].to_bytes(30, "big")
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class Otp(_Fixture):
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def test_a_decrypted_otp_passes_every_stage(self):
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path = self._write("otp.bin", _otp_plaintext())
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ok, reason = crypto_verify.verify_otp(
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path, _keys(ECC={"rootPublicXY": _root_public()})
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)
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self.assertTrue(ok, reason)
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self.assertIn("ECC cert valid", reason)
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def test_without_a_root_key_the_ecc_stage_is_skipped_not_faked(self):
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path = self._write("otp.bin", _otp_plaintext())
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ok, reason = crypto_verify.verify_otp(path, _keys())
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self.assertTrue(ok)
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self.assertIn("ECC skipped", reason)
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def test_wrong_size_is_refused(self):
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path = self._write("otp.bin", b"\x00" * 0xFF)
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ok, reason = crypto_verify.verify_otp(path, _keys())
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self.assertFalse(ok)
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self.assertIn("size mismatch", reason)
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def test_a_corrupted_body_fails_the_stored_hash(self):
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data = bytearray(_otp_plaintext())
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data[0x30] ^= 0xFF
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path = self._write("otp.bin", bytes(data))
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ok, reason = crypto_verify.verify_otp(path, _keys())
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self.assertFalse(ok)
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self.assertIn("SHA-256 hash mismatch", reason)
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def test_an_unsigned_certificate_is_refused(self):
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path = self._write("otp.bin", _otp_plaintext(sign=False))
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ok, reason = crypto_verify.verify_otp(
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path, _keys(ECC={"rootPublicXY": _root_public()})
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)
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self.assertFalse(ok)
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self.assertIn("ECC cert signature invalid", reason)
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def test_a_certificate_signed_for_another_console_is_refused(self):
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"""device_id feeds the signed name, so it cannot be swapped."""
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data = bytearray(_otp_plaintext(device_id=0x0A0B0C0D))
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struct.pack_into("<I", data, 0x04, 0x0A0B0C0E)
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body = bytes(data[:0xE0])
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path = self._write("otp.bin", body + hashlib.sha256(body).digest())
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ok, reason = crypto_verify.verify_otp(
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path, _keys(ECC={"rootPublicXY": _root_public()})
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)
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self.assertFalse(ok)
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self.assertIn("ECC cert signature invalid", reason)
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def test_the_pre_v5_expiry_endianness_is_honoured(self):
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path = self._write("otp.bin", _otp_plaintext(otp_version=4))
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ok, reason = crypto_verify.verify_otp(
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path, _keys(ECC={"rootPublicXY": _root_public()})
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)
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self.assertTrue(ok, reason)
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def test_a_dev_unit_uses_the_dev_issuer(self):
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path = self._write("otp.bin", _otp_plaintext(system_type=1))
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ok, reason = crypto_verify.verify_otp(
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path, _keys(ECC={"rootPublicXY": _root_public()})
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)
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self.assertTrue(ok, reason)
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def test_an_encrypted_otp_without_keys_says_so(self):
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path = self._write("otp.bin", b"\x11" * 0x100)
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ok, reason = crypto_verify.verify_otp(path, _keys())
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self.assertFalse(ok)
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self.assertIn("missing AES keys", reason)
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class Dispatch(_Fixture):
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"""check_crypto_validation is the entry point verify.py actually calls."""
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def test_an_unknown_filename_is_not_this_module_business(self):
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self.assertIsNone(
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crypto_verify.check_crypto_validation("x", "scph5501.bin", str(self.tmp))
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)
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def test_a_known_filename_without_a_keys_file_does_not_crash(self):
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path = self._write("movable.sed", b"\x00" * 0x120)
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result = crypto_verify.check_crypto_validation(
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str(path), "movable.sed", str(self.tmp)
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)
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self.assertIsInstance(result, (str, type(None)))
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def test_every_verifier_is_reachable_by_its_filename(self):
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self.assertEqual(
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sorted(crypto_verify._CRYPTO_VERIFIERS),
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["LocalFriendCodeSeed_B", "SecureInfo_A", "movable.sed", "otp.bin"],
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)
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if __name__ == "__main__":
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unittest.main()
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