yubi.py

from Crypto.Cipher import AES

def crc16(data):
    """
    Calculate an ISO13239 CRC checksum of the input buffer (bytestring).
    """
    m_crc = 0xffff
    for this in data:
        m_crc ^= ord(this)
        for _ in xrange(8):
            j = m_crc & 1
            m_crc >>= 1
            if j:
                m_crc ^= 0x8408
    return m_crc


otp = "cctglbkvkdglnnerijrlcldevckbbbninjccibignvln"
key = "a113f491bee316c628508b2e31fa8ca4".decode("hex")

mh = {
    'c': '0', 'b': '1', 'd': '2', 'e': '3', 
    'f': '4', 'g': '5', 'h': '6', 'i': '7',
    'j': '8', 'k': '9', 'l': 'a', 'n': 'b', 
    'r': 'c', 't': 'd', 'u': 'e', 'v': 'f'
}

mh_otp = ''.join(mh[i] for i in otp)
pub_id = mh_otp[:2*6] # length-6 id
msg = mh_otp[-32:].decode('hex')

cipher = AES.new(key, AES.MODE_ECB)
dec = cipher.decrypt(msg)
data = [ord(c) for c in dec]

assert(crc16(dec) == 0xf0b8)

# Parse data
response = {
    "uid": dec[0:6],
    "ctr": data[6] + (data[7] << 8),
    "tst": data[8] + (data[9] << 8) + (data[10] << 16),
    "scr": data[11],
    "rnd": data[12] + (data[13] << 8),
    "crc": data[14] + (data[15] << 8)
}