boltcard-writer/tests/test_vectors.py

"""Replays the worked examples of NXP AN12196 against our implementation.

Vectors transcribed from the application note (tables 14, 19, 20, 22, 27),
same set pylibsdm uses. No hardware needed.
"""

import pytest

from boltcard_writer import ntag424 as nt
from boltcard_writer.ntag424 import Ntag424, Ntag424Error, Session


class FakeTransport:
    def __init__(self, table: dict[str, str]):
        self.table = {k.upper(): v.upper() for k, v in table.items()}
        self.sent: list[str] = []

    def transmit(self, apdu: bytes) -> bytes:
        h = apdu.hex().upper()
        self.sent.append(h)
        if h not in self.table:
            raise AssertionError(f"unexpected APDU {h}")
        return bytes.fromhex(self.table[h])


AUTH_TABLE = {
    "00A4040007D276000085010100": "9000",
    # key 0, RndA = 13C5DB8A5930439FC3DEF9A4C675360F
    "9071000002000000": "A04C124213C186F22399D33AC2A3021591AF",
    "90AF00002035C3E05A752E0144BAC0DE51C1F22C56B34408A23D8AEA266CAB947EA8E0118D00": "3FA64DB5446D1F34CD6EA311167F5E4985B89690C04A05F17FA7AB2F081206639100",
    # key 3, RndA = B98F4C50CF1C2E084FD150E33992B048
    "9071000002030000": "B875CEB0E66A6C5CD00898DC371F92D191AF",
    "90AF000020FF0306E47DFBC50087C4D8A78E88E62DE1E8BE457AA477C707E2F0874916A8B100": "0CC9A8094A8EEA683ECAAC5C7BF20584206D0608D477110FC6B3D5D3F65C3A6A9100",
}


def test_authenticate_ev2_first_key0():
    t = FakeTransport(AUTH_TABLE)
    tag = Ntag424(t)
    tag.select_application()
    s = tag.authenticate_ev2_first(0, nt.ZERO_KEY, rnd_a=bytes.fromhex("13C5DB8A5930439FC3DEF9A4C675360F"))
    assert s.ti == bytes.fromhex("9D00C4DF")
    assert s.enc_key == bytes.fromhex("1309C877509E5A215007FF0ED19CA564")
    assert s.mac_key == bytes.fromhex("4C6626F5E72EA694202139295C7A7FC7")
    assert s.cmd_ctr == 0


def test_authenticate_ev2_first_key3():
    t = FakeTransport(AUTH_TABLE)
    tag = Ntag424(t)
    s = tag.authenticate_ev2_first(3, nt.ZERO_KEY, rnd_a=bytes.fromhex("B98F4C50CF1C2E084FD150E33992B048"))
    assert s.ti == bytes.fromhex("7614281A")
    assert s.enc_key == bytes.fromhex("7A93D6571E4B180FCA6AC90C9A7488D4")
    assert s.mac_key == bytes.fromhex("FC4AF159B62E549B5812394CAB1918CC")


def test_authenticate_detects_wrong_rnda():
    table = dict(AUTH_TABLE)
    # tamper the part-2 response
    table["90AF00002035C3E05A752E0144BAC0DE51C1F22C56B34408A23D8AEA266CAB947EA8E0118D00"] = "00" * 32 + "9100"
    tag = Ntag424(FakeTransport(table))
    with pytest.raises(Ntag424Error, match="RndA"):
        tag.authenticate_ev2_first(0, nt.ZERO_KEY, rnd_a=bytes.fromhex("13C5DB8A5930439FC3DEF9A4C675360F"))


def _session(enc: str, mac: str, ti: str, ctr: int, key_no: int = 0) -> Session:
    return Session(key_no=key_no, ti=bytes.fromhex(ti), enc_key=bytes.fromhex(enc), mac_key=bytes.fromhex(mac), cmd_ctr=ctr)


def test_iv_cmd():
    s = _session("4CF3CB41A22583A61E89B158D252FC53", "00" * 16, "7614281A", 3)
    assert s.iv_cmd() == bytes.fromhex("01602D579423B2797BE8B478B0B4D27B")


def test_change_key_0():
    t = FakeTransport({"90C400002900C0EB4DEEFEDDF0B513A03A95A75491818580503190D4D05053FF75668A01D6FDA6610234BDED643200": "9100"})
    tag = Ntag424(t)
    tag.session = _session("4CF3CB41A22583A61E89B158D252FC53", "5529860B2FC5FB6154B7F28361D30BF9", "7614281A", 3)
    tag.change_key(0, bytes.fromhex("5004BF991F408672B1EF00F08F9E8647"), version=1)
    assert tag.session is None  # changing key 0 ends the session


def test_change_key_2_and_response_mac():
    t = FakeTransport(
        {"90C4000029022CF362B7BF4311FF3BE1DAA295E8C68DE09050560D19B9E16C2393AE9CD1FAC75D0CE20BCD1D06E600": "203BB55D1089D5879100"}
    )
    tag = Ntag424(t)
    tag.session = _session("4CF3CB41A22583A61E89B158D252FC53", "5529860B2FC5FB6154B7F28361D30BF9", "7614281A", 2)
    tag.change_key(2, bytes.fromhex("F3847D627727ED3BC9C4CC050489B966"), nt.ZERO_KEY, version=1)
    assert tag.session is not None and tag.session.cmd_ctr == 3


def test_change_key_bad_response_mac():
    t = FakeTransport(
        {"90C4000029022CF362B7BF4311FF3BE1DAA295E8C68DE09050560D19B9E16C2393AE9CD1FAC75D0CE20BCD1D06E600": "00000000000000009100"}
    )
    tag = Ntag424(t)
    tag.session = _session("4CF3CB41A22583A61E89B158D252FC53", "5529860B2FC5FB6154B7F28361D30BF9", "7614281A", 2)
    with pytest.raises(Ntag424Error, match="MAC"):
        tag.change_key(2, bytes.fromhex("F3847D627727ED3BC9C4CC050489B966"), nt.ZERO_KEY, version=1)


def test_write_data_full():
    t = FakeTransport({"908D00001F030000000A00006B5E6804909962FC4E3FF5522CF0F8436C0C53315B9C73AA00": "C26D236E4A7C046D9100"})
    tag = Ntag424(t)
    tag.session = _session("7A93D6571E4B180FCA6AC90C9A7488D4", "FC4AF159B62E549B5812394CAB1918CC", "7614281A", 0, key_no=3)
    tag.write_data(3, 0, bytes.fromhex("0102030405060708090A"))
    assert tag.session.cmd_ctr == 1


def test_change_file_settings_an12196_table19():
    """AN12196 table 19 (SDM enabled, offsets 32/67/67). pylibsdm marks this
    vector as broken in the spec; we keep it as a regression check on our
    encoding path and skip if it ever disagrees with the note."""
    expected = "905F0000190261B6D97903566E84C3AE5274467E89EAD799B7C1A0EF7A0400"
    settings = bytes.fromhex("4000E0C1F121") + nt.le3(32) + nt.le3(67) + nt.le3(67)
    t = FakeTransport({expected: "9100" + "00" * 0})
    tag = Ntag424(t)
    tag.session = _session("1309C877509E5A215007FF0ED19CA564", "4C6626F5E72EA694202139295C7A7FC7", "9D00C4DF", 0)
    try:
        tag.change_file_settings(2, settings)
    except AssertionError as e:
        pytest.xfail(f"spec vector mismatch: {e}")
    except Ntag424Error:
        pass  # the fake returned no MAC; the APDU itself matched, which is what we check


def test_crc32_nk_and_helpers():
    # JAMCRC of "123456789" is 0x340BC6D9 (standard CRC-32 is 0xCBF43926)
    assert nt.crc32_nk(b"123456789") == (0x340BC6D9).to_bytes(4, "little")
    assert nt.truncate_mac(bytes(range(16))) == bytes([1, 3, 5, 7, 9, 11, 13, 15])
    assert nt.rotate_left(b"\x01\x02\x03") == b"\x02\x03\x01"
    assert nt.pad_enc(b"\x01" * 16) == b"\x01" * 16 + b"\x80" + bytes(15)
    assert nt.unpad_enc(nt.pad_enc(b"abc")) == b"abc"


def test_status_error_clears_session():
    t = FakeTransport({"90640000010100": "919D"})
    tag = Ntag424(t)
    tag.session = _session("00" * 16, "00" * 16, "00000000", 0)
    with pytest.raises(Ntag424Error, match="PERMISSION_DENIED"):
        tag.get_key_version(1)
    assert tag.session is None