#!/usr/bin/env python3

import argparse
import binascii
import socket
import struct

CRC32_TABLE = [
    0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4, 0xc79a971f, 0x35f1141c, 0x26a1e7e8, 0xd4ca64eb,
    0x8ad958cf, 0x78b2dbcc, 0x6be22838, 0x9989ab3b, 0x4d43cfd0, 0xbf284cd3, 0xac78bf27, 0x5e133c24,
    0x105ec76f, 0xe235446c, 0xf165b798, 0x030e349b, 0xd7c45070, 0x25afd373, 0x36ff2087, 0xc494a384,
    0x9a879fa0, 0x68ec1ca3, 0x7bbcef57, 0x89d76c54, 0x5d1d08bf, 0xaf768bbc, 0xbc267848, 0x4e4dfb4b,
    0x20bd8ede, 0xd2d60ddd, 0xc186fe29, 0x33ed7d2a, 0xe72719c1, 0x154c9ac2, 0x061c6936, 0xf477ea35,
    0xaa64d611, 0x580f5512, 0x4b5fa6e6, 0xb93425e5, 0x6dfe410e, 0x9f95c20d, 0x8cc531f9, 0x7eaeb2fa,
    0x30e349b1, 0xc288cab2, 0xd1d83946, 0x23b3ba45, 0xf779deae, 0x05125dad, 0x1642ae59, 0xe4292d5a,
    0xba3a117e, 0x4851927d, 0x5b016189, 0xa96ae28a, 0x7da08661, 0x8fcb0562, 0x9c9bf696, 0x6ef07595,
    0x417b1dbc, 0xb3109ebf, 0xa0406d4b, 0x522bee48, 0x86e18aa3, 0x748a09a0, 0x67dafa54, 0x95b17957,
    0xcba24573, 0x39c9c670, 0x2a993584, 0xd8f2b687, 0x0c38d26c, 0xfe53516f, 0xed03a29b, 0x1f682198,
    0x5125dad3, 0xa34e59d0, 0xb01eaa24, 0x42752927, 0x96bf4dcc, 0x64d4cecf, 0x77843d3b, 0x85efbe38,
    0xdbfc821c, 0x2997011f, 0x3ac7f2eb, 0xc8ac71e8, 0x1c661503, 0xee0d9600, 0xfd5d65f4, 0x0f36e6f7,
    0x61c69362, 0x93ad1061, 0x80fde395, 0x72966096, 0xa65c047d, 0x5437877e, 0x4767748a, 0xb50cf789,
    0xeb1fcbad, 0x197448ae, 0x0a24bb5a, 0xf84f3859, 0x2c855cb2, 0xdeeedfb1, 0xcdbe2c45, 0x3fd5af46,
    0x7198540d, 0x83f3d70e, 0x90a324fa, 0x62c8a7f9, 0xb602c312, 0x44694011, 0x5739b3e5, 0xa55230e6,
    0xfb410cc2, 0x092a8fc1, 0x1a7a7c35, 0xe811ff36, 0x3cdb9bdd, 0xceb018de, 0xdde0eb2a, 0x2f8b6829,
    0x82f63b78, 0x709db87b, 0x63cd4b8f, 0x91a6c88c, 0x456cac67, 0xb7072f64, 0xa457dc90, 0x563c5f93,
    0x082f63b7, 0xfa44e0b4, 0xe9141340, 0x1b7f9043, 0xcfb5f4a8, 0x3dde77ab, 0x2e8e845f, 0xdce5075c,
    0x92a8fc17, 0x60c37f14, 0x73938ce0, 0x81f80fe3, 0x55326b08, 0xa759e80b, 0xb4091bff, 0x466298fc,
    0x1871a4d8, 0xea1a27db, 0xf94ad42f, 0x0b21572c, 0xdfeb33c7, 0x2d80b0c4, 0x3ed04330, 0xccbbc033,
    0xa24bb5a6, 0x502036a5, 0x4370c551, 0xb11b4652, 0x65d122b9, 0x97baa1ba, 0x84ea524e, 0x7681d14d,
    0x2892ed69, 0xdaf96e6a, 0xc9a99d9e, 0x3bc21e9d, 0xef087a76, 0x1d63f975, 0x0e330a81, 0xfc588982,
    0xb21572c9, 0x407ef1ca, 0x532e023e, 0xa145813d, 0x758fe5d6, 0x87e466d5, 0x94b49521, 0x66df1622,
    0x38cc2a06, 0xcaa7a905, 0xd9f75af1, 0x2b9cd9f2, 0xff56bd19, 0x0d3d3e1a, 0x1e6dcdee, 0xec064eed,
    0xc38d26c4, 0x31e6a5c7, 0x22b65633, 0xd0ddd530, 0x0417b1db, 0xf67c32d8, 0xe52cc12c, 0x1747422f,
    0x49547e0b, 0xbb3ffd08, 0xa86f0efc, 0x5a048dff, 0x8ecee914, 0x7ca56a17, 0x6ff599e3, 0x9d9e1ae0,
    0xd3d3e1ab, 0x21b862a8, 0x32e8915c, 0xc083125f, 0x144976b4, 0xe622f5b7, 0xf5720643, 0x07198540,
    0x590ab964, 0xab613a67, 0xb831c993, 0x4a5a4a90, 0x9e902e7b, 0x6cfbad78, 0x7fab5e8c, 0x8dc0dd8f,
    0xe330a81a, 0x115b2b19, 0x020bd8ed, 0xf0605bee, 0x24aa3f05, 0xd6c1bc06, 0xc5914ff2, 0x37faccf1,
    0x69e9f0d5, 0x9b8273d6, 0x88d28022, 0x7ab90321, 0xae7367ca, 0x5c18e4c9, 0x4f48173d, 0xbd23943e,
    0xf36e6f75, 0x0105ec76, 0x12551f82, 0xe03e9c81, 0x34f4f86a, 0xc69f7b69, 0xd5cf889d, 0x27a40b9e,
    0x79b737ba, 0x8bdcb4b9, 0x988c474d, 0x6ae7c44e, 0xbe2da0a5, 0x4c4623a6, 0x5f16d052, 0xad7d5351,
]


def crc32(data, init=0):
    """CRC32-C (Castagnoli)"""
    crc = init
    for byte in data:
        crc = CRC32_TABLE[(crc & 0xff) ^ int(byte)] ^ (crc >> 8)
    return crc


def test_crc32():
    """Test CRC32 implementation for consistency with C code."""
    assert crc32([]) == 0
    assert crc32([1], 2) == 324072436
    assert crc32([1, 2], 3) == 3330162713
    assert crc32([1, 2, 3], 4) == 260765054
    assert crc32([1, 2, 3, 4], 5) == 3341835384
    assert crc32([1, 2, 3, 4, 5], 6) == 2252642422
    assert crc32([1, 2, 3, 4, 5, 6], 7) == 2653846412
    assert crc32([1, 2, 3, 4, 5, 6, 7], 8) == 1210708962


# Protocol constants
MCR_LENGTH = 400
MCR_REQUEST = b'MCRH3110'
MCR_CHALLENGE = b'MCRC'
MCR_RESPONSE = b'MCRR'


def recvall(channel, length):
    """Receive exactly `length` bytes from socket."""
    message = b''
    while len(message) < length:
        message += channel.recv(length - len(message))
    return message


def pad(message):
    """Right-pad message with zero bytes to `MCR_LENGTH`."""
    return message + b'\x00' * (MCR_LENGTH - len(message))


def run_tcp_client(options):
    with socket.create_connection((options.host, options.port)) as channel:
        request = pad(MCR_REQUEST)
        channel.sendall(request)

        challenge = recvall(channel, 8)
        signature, cookie = challenge[:4], challenge[4:]

        assert signature == MCR_CHALLENGE
        print(f'cookie received: {binascii.hexlify(cookie)}')

        hash = crc32(cookie + options.key)
        hash = struct.pack('>I', hash)

        print(f'sending hash: {binascii.hexlify(hash)}')

        response = pad(MCR_RESPONSE + hash)
        channel.sendall(response)


def run_tcp_server(options):
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM, socket.IPPROTO_TCP) as listener:
        listener.bind((options.host, options.port))
        listener.listen(1)
        (client, address) = listener.accept()
        with client:
            print(f'client connected: {address}')

            request = recvall(client, MCR_LENGTH)
            print('request receiced')

            assert request == pad(MCR_REQUEST)

            # cookie calculation method may differ and not use CRC32 at all
            if options.cookie:
                cookie = options.cookie
            else:
                cookie = crc32(bytes(repr(address), encoding='utf-8'))
                cookie = struct.pack('>I', cookie)

            challenge = MCR_CHALLENGE + cookie
            client.sendall(challenge)
            print('challenge sent')

            response = recvall(client, MCR_LENGTH)
            print('response received')

            signature, hash = response[:4], struct.unpack('>I', response[4:8])[0]
            assert signature == MCR_RESPONSE

            valid_hash = crc32(cookie + options.key)
            assert hash == valid_hash, f'invalid hash {hash}, expected {valid_hash}'

            print(f'authentication successful')


def run_udp_client(options):
    with socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP) as channel:
        server = (options.host, options.port)

        request = pad(MCR_REQUEST)
        channel.sendto(request, server)

        challenge, _ = channel.recvfrom(MCR_LENGTH)
        signature, cookie = struct.unpack('4s4s', challenge)

        assert signature == MCR_CHALLENGE
        print(f'challenge received: {binascii.hexlify(cookie)}')

        hash1 = crc32(cookie + options.key)
        hash2 = crc32(cookie, hash1)
        print(f'sending hashes: {hash1:08x} {hash2:08x}')

        response = pad(struct.pack('<4s4sII', MCR_RESPONSE, cookie, hash1, hash2))
        channel.sendto(response, server)


def run_udp_server(options):
    with socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP) as client:
        client.bind((options.host, options.port))

        request, address = client.recvfrom(MCR_LENGTH)
        assert request == pad(MCR_REQUEST)
        print(f'request received: {address}')

        # cookie calculation method may differ and not use CRC32 at all
        if options.cookie:
            cookie = options.cookie
        else:
            cookie = crc32(bytes(repr(address), encoding='utf-8'))
            cookie = struct.pack('<I', cookie)

        challenge = MCR_CHALLENGE + cookie
        client.sendto(challenge, address)
        print('challenge sent')

        response, address = client.recvfrom(MCR_LENGTH)
        print(f'response received: {address}')

        signature, response_cookie, hash1, hash2 = \
                struct.unpack('<4s4sII', response[:16])
        assert signature == MCR_RESPONSE
        assert response_cookie == cookie

        valid_hash1 = crc32(cookie + options.key)
        valid_hash2 = crc32(cookie, valid_hash1)
        assert hash1 == valid_hash1, f'hash1: want {valid_hash1:08x}, got {hash1:08x}'
        assert hash2 == valid_hash2, f'hash2: want {valid_hash2:08x}, got {hash2:08x}'
        print(f'authentication successful')


def parse_options():
    parser = argparse.ArgumentParser(description='MCR protocol reference implementation')
    parser.add_argument('--host', default='127.0.0.1')
    parser.add_argument('--port', default=1234, type=int)
    parser.add_argument('--udp', action='store_true', help='authenticate using UDP')
    parser.add_argument('--key_hex', help='secret key (hex string)')
    parser.add_argument('--key_raw', help='secret key (plaintext)')

    subs = parser.add_subparsers(dest='action')

    subs.add_parser('client')

    server = subs.add_parser('server')
    server.add_argument('--cookie', help='predefined cookie (hex string)')

    options = parser.parse_args()

    if options.key_hex:
        options.key = binascii.unhexlify(options.key_hex)
    elif options.key_raw:
        options.key = bytes(options.key_raw, 'utf-8')
    assert options.key, 'either --key_hex or --key_raw is required'
    assert len(options.key) >= 8

    if hasattr(options, 'cookie') and (options.cookie is not None):
        options.cookie = binascii.unhexlify(options.cookie)
        assert len(options.cookie) == 4
    else:
        options.cookie = None
    return options


if __name__ == '__main__':
    test_crc32()

    options = parse_options()
    if not options.udp:
        if options.action == 'client':
            run_tcp_client(options)
        else:
            run_tcp_server(options)
    else:
        if options.action == 'client':
            run_udp_client(options)
        else:
            run_udp_server(options)