# Copyright (c) 2023 Yubico AB
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from __future__ import annotations

import abc
import logging
import os
import struct
from dataclasses import dataclass, field
from enum import IntEnum, unique
from typing import Callable, NamedTuple, Sequence

from cryptography import x509
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import cmac, constant_time, hashes, serialization
from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.primitives.kdf.x963kdf import X963KDF

from .. import BadResponseError, Tlv

logger = logging.getLogger(__name__)


INS_INITIALIZE_UPDATE = 0x50
INS_EXTERNAL_AUTHENTICATE = 0x82
INS_INTERNAL_AUTHENTICATE = 0x88
INS_PERFORM_SECURITY_OPERATION = 0x2A

_DEFAULT_KEY = b"\x40\x41\x42\x43\x44\x45\x46\x47\x48\x49\x4a\x4b\x4c\x4d\x4e\x4f"

_KEY_ENC = 0x04
_KEY_MAC = 0x06
_KEY_RMAC = 0x07
_CARD_CRYPTOGRAM = 0x00
_HOST_CRYPTOGRAM = 0x01


def _derive(key: bytes, t: int, context: bytes, L: int = 0x80) -> bytes:
    # this only supports aes128
    if L != 0x80 and L != 0x40:
        raise ValueError("L must be 0x40 or 0x80")

    i = b"\0" * 11 + struct.pack("!BBHB", t, 0, L, 1) + context

    c = cmac.CMAC(algorithms.AES(key), backend=default_backend())
    c.update(i)
    return c.finalize()[: L // 8]


def _calculate_mac(key: bytes, chain: bytes, message: bytes) -> tuple[bytes, bytes]:
    c = cmac.CMAC(algorithms.AES(key), backend=default_backend())
    c.update(chain)
    c.update(message)
    chain = c.finalize()
    return chain, chain[:8]


def _init_cipher(key: bytes, counter: int, response=False) -> Cipher:
    encryptor = Cipher(
        algorithms.AES(key),
        modes.ECB(),  # noqa: S305
        backend=default_backend(),
    ).encryptor()
    iv_data = (b"\x80" if response else b"\x00") + int.to_bytes(counter, 15, "big")
    iv = encryptor.update(iv_data) + encryptor.finalize()
    return Cipher(
        algorithms.AES(key),
        modes.CBC(iv),
        backend=default_backend(),
    )


class SessionKeys(NamedTuple):
    """SCP Session Keys."""

    key_senc: bytes
    key_smac: bytes
    key_srmac: bytes
    key_dek: bytes | None = None


class StaticKeys(NamedTuple):
    """SCP03 Static Keys."""

    key_enc: bytes
    key_mac: bytes
    key_dek: bytes | None = None

    @classmethod
    def default(cls) -> StaticKeys:
        return cls(_DEFAULT_KEY, _DEFAULT_KEY, _DEFAULT_KEY)

    def derive(self, context: bytes) -> SessionKeys:
        return SessionKeys(
            _derive(self.key_enc, _KEY_ENC, context),
            _derive(self.key_mac, _KEY_MAC, context),
            _derive(self.key_mac, _KEY_RMAC, context),
            self.key_dek,
        )


@unique
class ScpKid(IntEnum):
    SCP03 = 0x1
    SCP11a = 0x11
    SCP11b = 0x13
    SCP11c = 0x15


class KeyRef(bytes):
    @property
    def kid(self) -> int:
        return self[0]

    @property
    def kvn(self) -> int:
        return self[1]

    def __new__(cls, kid_or_data: int | bytes, kvn: int | None = None):
        """This allows creation by passing either binary data, or kid and kvn."""
        if isinstance(kid_or_data, int):  # kid and kvn
            if kvn is None:
                raise ValueError("Missing kvn")
            data = bytes([kid_or_data, kvn])
        else:  # Binary id and version
            if kvn is not None:
                raise ValueError("kvn can only be provided if kid_or_data is a kid")
            data = kid_or_data

        # mypy thinks this is wrong
        return super(KeyRef, cls).__new__(cls, data)  # type: ignore

    def __init__(self, kid_or_data: int | bytes, kvn: int | None = None):
        if len(self) != 2:
            raise ValueError("Incorrect length")

    def __repr__(self):
        return f"KeyRef(kid=0x{self.kid:02x}, kvn=0x{self.kvn:02x})"

    def __str__(self):
        return repr(self)


@dataclass(frozen=True)
class ScpKeyParams(abc.ABC):
    ref: KeyRef


@dataclass(frozen=True)
class Scp03KeyParams(ScpKeyParams):
    ref: KeyRef = KeyRef(ScpKid.SCP03, 0)
    keys: StaticKeys = StaticKeys.default()


@dataclass(frozen=True)
class Scp11KeyParams(ScpKeyParams):
    pk_sd_ecka: ec.EllipticCurvePublicKey
    # For SCP11 a/c we need an OCE key, with its trust chain
    oce_ref: KeyRef | None = None
    sk_oce_ecka: ec.EllipticCurvePrivateKey | None = None
    # Certificate chain for sk_oce_ecka, leaf-last order
    certificates: Sequence[x509.Certificate] = field(default_factory=list)


SendApdu = Callable[[int, int, int, int, bytes], bytes]


class ScpState:
    def __init__(
        self,
        session_keys: SessionKeys,
        mac_chain: bytes = b"\0" * 16,
        enc_counter: int = 1,
    ):
        self._keys = session_keys
        self._mac_chain = mac_chain
        self._enc_counter = enc_counter

    def encrypt(self, data: bytes) -> bytes:
        # Pad the data
        msg = data
        padlen = 15 - len(msg) % 16
        msg += b"\x80"
        msg = msg.ljust(len(msg) + padlen, b"\0")

        # Encrypt
        cipher = _init_cipher(self._keys.key_senc, self._enc_counter)
        encryptor = cipher.encryptor()
        encrypted = encryptor.update(msg) + encryptor.finalize()
        self._enc_counter += 1
        return encrypted

    def mac(self, data: bytes) -> bytes:
        next_mac_chain, mac = _calculate_mac(self._keys.key_smac, self._mac_chain, data)
        self._mac_chain = next_mac_chain
        return mac

    def unmac(self, data: bytes, sw: int) -> bytes:
        msg, mac = data[:-8], data[-8:]
        rmac = _calculate_mac(
            self._keys.key_srmac, self._mac_chain, msg + struct.pack("!H", sw)
        )[1]
        if not constant_time.bytes_eq(mac, rmac):
            raise BadResponseError("Wrong MAC")
        return msg

    def decrypt(self, encrypted: bytes) -> bytes:
        # Decrypt
        cipher = _init_cipher(self._keys.key_senc, self._enc_counter - 1, True)
        decryptor = cipher.decryptor()
        decrypted = decryptor.update(encrypted) + decryptor.finalize()

        # Unpad
        unpadded = decrypted.rstrip(b"\x00")
        if unpadded[-1] != 0x80:
            raise BadResponseError("Wrong padding")
        unpadded = unpadded[:-1]

        return unpadded

    @classmethod
    def scp03_init(
        cls,
        send_apdu: SendApdu,
        key_params: Scp03KeyParams,
        *,
        host_challenge: bytes | None = None,
    ) -> tuple[ScpState, bytes]:
        logger.debug("Initializing SCP03 handshake")
        host_challenge = host_challenge or os.urandom(8)
        resp = send_apdu(
            0x80, INS_INITIALIZE_UPDATE, key_params.ref.kvn, 0x00, host_challenge
        )

        diversification_data = resp[:10]  # noqa: F841
        key_info = resp[10:13]  # noqa: F841
        card_challenge = resp[13:21]
        card_cryptogram = resp[21:29]

        context = host_challenge + card_challenge
        session_keys = key_params.keys.derive(context)

        gen_card_crypto = _derive(
            session_keys.key_smac, _CARD_CRYPTOGRAM, context, 0x40
        )
        if not constant_time.bytes_eq(gen_card_crypto, card_cryptogram):
            # This means wrong keys
            raise BadResponseError("Wrong SCP03 key set")

        host_cryptogram = _derive(
            session_keys.key_smac, _HOST_CRYPTOGRAM, context, 0x40
        )

        return cls(session_keys), host_cryptogram

    @classmethod
    def scp11_init(
        cls,
        send_apdu: SendApdu,
        key_params: Scp11KeyParams,
    ) -> ScpState:
        kid = ScpKid(key_params.ref.kid)
        logger.debug(f"Initializing {kid.name} handshake")

        # GPC v2.3 Amendment F (SCP11) v1.4 §7.1.1
        if kid == ScpKid.SCP11a:
            params = 0b01
        elif kid == ScpKid.SCP11b:
            params = 0b00
        elif kid == ScpKid.SCP11c:
            params = 0b11
        else:
            raise ValueError("Invalid SCP KID")

        if kid in (ScpKid.SCP11a, ScpKid.SCP11c):
            # GPC v2.3 Amendment F (SCP11) v1.4 §7.5
            assert key_params.sk_oce_ecka  # noqa: S101
            n = len(key_params.certificates) - 1
            assert n >= 0  # noqa: S101
            oce_ref = key_params.oce_ref or KeyRef(0, 0)
            logger.debug("Sending certificate chain")
            for i, cert in enumerate(key_params.certificates):
                p2 = oce_ref.kid | (0x80 if i < n else 0)
                data = cert.public_bytes(serialization.Encoding.DER)
                logger.debug(f"Sending cert: {cert.subject}")
                send_apdu(0x80, INS_PERFORM_SECURITY_OPERATION, oce_ref.kvn, p2, data)

        key_usage = bytes(
            [0x3C]
        )  # AUTHENTICATED | C_MAC | C_DECRYPTION | R_MAC | R_ENCRYPTION
        key_type = bytes([0x88])  # AES
        key_len = bytes([16])  # 128-bit

        # Host ephemeral key
        esk_oce_ecka = ec.generate_private_key(key_params.pk_sd_ecka.curve)
        epk_oce_ecka = esk_oce_ecka.public_key()

        # GPC v2.3 Amendment F (SCP11) v1.4 §7.6.2.3
        data = Tlv(
            0xA6,
            Tlv(0x90, bytes([0x11, params]))
            + Tlv(0x95, key_usage)
            + Tlv(0x80, key_type)
            + Tlv(0x81, key_len),
        ) + Tlv(
            0x5F49,
            epk_oce_ecka.public_bytes(
                serialization.Encoding.X962,
                serialization.PublicFormat.UncompressedPoint,
            ),
        )

        # Static host key (SCP11a/c), or ephemeral key again (SCP11b)
        sk_oce_ecka = key_params.sk_oce_ecka or esk_oce_ecka

        logger.debug("Performing key agreement")
        ins = (
            INS_INTERNAL_AUTHENTICATE
            if key_params.ref.kid == ScpKid.SCP11b
            else INS_EXTERNAL_AUTHENTICATE
        )
        resp = send_apdu(0x80, ins, key_params.ref.kvn, key_params.ref.kid, data)

        epk_sd_ecka_tlv, resp = Tlv.parse_from(resp)
        epk_sd_ecka = Tlv.unpack(0x5F49, epk_sd_ecka_tlv)
        receipt = Tlv.unpack(0x86, resp)

        # GPC v2.3 Amendment F (SCP11) v1.3 §3.1.2 Key Derivation
        key_agreement_data = data + epk_sd_ecka_tlv
        sharedinfo = key_usage + key_type + key_len
        keys = X963KDF(hashes.SHA256(), 5 * key_len[0], sharedinfo).derive(
            esk_oce_ecka.exchange(
                ec.ECDH(),
                ec.EllipticCurvePublicKey.from_encoded_point(
                    sk_oce_ecka.curve, epk_sd_ecka
                ),
            )
            + sk_oce_ecka.exchange(ec.ECDH(), key_params.pk_sd_ecka)
        )

        # 5 keys were derived, one for verification of receipt
        ln = key_len[0]
        keys = [keys[i : i + ln] for i in range(0, ln * 5, ln)]
        c = cmac.CMAC(algorithms.AES(keys.pop(0)))
        c.update(key_agreement_data)
        c.verify(receipt)
        # The 4 remaining keys are session keys
        session_keys = SessionKeys(*keys)

        return cls(session_keys, receipt)
