skip32

skip32.py

# -*- coding: utf-8 -*-

from functools import partial


SKIP32_FTABLE = [
    0xa3, 0xd7, 0x09, 0x83, 0xf8, 0x48, 0xf6, 0xf4,
    0xb3, 0x21, 0x15, 0x78, 0x99, 0xb1, 0xaf, 0xf9,
    0xe7, 0x2d, 0x4d, 0x8a, 0xce, 0x4c, 0xca, 0x2e,
    0x52, 0x95, 0xd9, 0x1e, 0x4e, 0x38, 0x44, 0x28,
    0x0a, 0xdf, 0x02, 0xa0, 0x17, 0xf1, 0x60, 0x68,
    0x12, 0xb7, 0x7a, 0xc3, 0xe9, 0xfa, 0x3d, 0x53,
    0x96, 0x84, 0x6b, 0xba, 0xf2, 0x63, 0x9a, 0x19,
    0x7c, 0xae, 0xe5, 0xf5, 0xf7, 0x16, 0x6a, 0xa2,
    0x39, 0xb6, 0x7b, 0x0f, 0xc1, 0x93, 0x81, 0x1b,
    0xee, 0xb4, 0x1a, 0xea, 0xd0, 0x91, 0x2f, 0xb8,
    0x55, 0xb9, 0xda, 0x85, 0x3f, 0x41, 0xbf, 0xe0,
    0x5a, 0x58, 0x80, 0x5f, 0x66, 0x0b, 0xd8, 0x90,
    0x35, 0xd5, 0xc0, 0xa7, 0x33, 0x06, 0x65, 0x69,
    0x45, 0x00, 0x94, 0x56, 0x6d, 0x98, 0x9b, 0x76,
    0x97, 0xfc, 0xb2, 0xc2, 0xb0, 0xfe, 0xdb, 0x20,
    0xe1, 0xeb, 0xd6, 0xe4, 0xdd, 0x47, 0x4a, 0x1d,
    0x42, 0xed, 0x9e, 0x6e, 0x49, 0x3c, 0xcd, 0x43,
    0x27, 0xd2, 0x07, 0xd4, 0xde, 0xc7, 0x67, 0x18,
    0x89, 0xcb, 0x30, 0x1f, 0x8d, 0xc6, 0x8f, 0xaa,
    0xc8, 0x74, 0xdc, 0xc9, 0x5d, 0x5c, 0x31, 0xa4,
    0x70, 0x88, 0x61, 0x2c, 0x9f, 0x0d, 0x2b, 0x87,
    0x50, 0x82, 0x54, 0x64, 0x26, 0x7d, 0x03, 0x40,
    0x34, 0x4b, 0x1c, 0x73, 0xd1, 0xc4, 0xfd, 0x3b,
    0xcc, 0xfb, 0x7f, 0xab, 0xe6, 0x3e, 0x5b, 0xa5,
    0xad, 0x04, 0x23, 0x9c, 0x14, 0x51, 0x22, 0xf0,
    0x29, 0x79, 0x71, 0x7e, 0xff, 0x8c, 0x0e, 0xe2,
    0x0c, 0xef, 0xbc, 0x72, 0x75, 0x6f, 0x37, 0xa1,
    0xec, 0xd3, 0x8e, 0x62, 0x8b, 0x86, 0x10, 0xe8,
    0x08, 0x77, 0x11, 0xbe, 0x92, 0x4f, 0x24, 0xc5,
    0x32, 0x36, 0x9d, 0xcf, 0xf3, 0xa6, 0xbb, 0xac,
    0x5e, 0x6c, 0xa9, 0x13, 0x57, 0x25, 0xb5, 0xe3,
    0xbd, 0xa8, 0x3a, 0x01, 0x05, 0x59, 0x2a, 0x46,
]


def skip32_op(op, data, key):
    assert isinstance(data, int) and data & 0xFFFFFFFF == data, 'data should be int32'
    assert isinstance(key, str) and len(key) == 10, 'key should be 80bit string'

    key = [ord(i) for i in key]

    def g(k, w):
        g1 = (w >> 8) & 0xFF
        g2 = w & 0xFF

        g3 = SKIP32_FTABLE[g2 ^ key[(4 * k) % 10]] ^ g1
        g4 = SKIP32_FTABLE[g3 ^ key[(4 * k + 1) % 10]] ^ g2
        g5 = SKIP32_FTABLE[g4 ^ key[(4 * k + 2) % 10]] ^ g3
        g6 = SKIP32_FTABLE[g5 ^ key[(4 * k + 3) % 10]] ^ g4

        return (g5 << 8) + g6

    if op:
        kstep = 1
        k = 0
    else:
        kstep = -1
        k = 23

    # assuming littie-endian
    wl = data & 0xFFFF
    wr = data >> 16

    for i in xrange(0, 24 / 2):
        wr ^= g(k, wl) ^ k
        k += kstep
        wl ^= g(k, wr) ^ k
        k += kstep

    return (wl << 16) + wr


encrypt = partial(skip32_op, 1)
decrypt = partial(skip32_op, 0)