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"""
utility functions for Yubico modules
"""
# Copyright (c) 2010, Yubico AB
# See the file COPYING for licence statement.
__all__ = [
# constants
# functions
'crc16',
'validate_crc16',
'hexdump',
'modhex_decode',
'hotp_truncate',
# classes
]
import sys
import string
from .yubico_version import __version__
from . import yubikey_defs
from . import yubico_exception
_CRC_OK_RESIDUAL = 0xf0b8
def ord_byte(byte):
"""Convert a byte to its integer value"""
if sys.version_info < (3, 0):
return ord(byte)
else:
# In Python 3, single bytes are represented as integers
return int(byte)
def chr_byte(number):
"""Convert an integer value to a length-1 bytestring"""
if sys.version_info < (3, 0):
return chr(number)
else:
return bytes([number])
def crc16(data):
"""
Calculate an ISO13239 CRC checksum of the input buffer (bytestring).
"""
m_crc = 0xffff
for this in data:
m_crc ^= ord_byte(this)
for _ in range(8):
j = m_crc & 1
m_crc >>= 1
if j:
m_crc ^= 0x8408
return m_crc
def validate_crc16(data):
"""
Validate that the CRC of the contents of buffer is the residual OK value.
The input is a bytestring.
"""
return crc16(data) == _CRC_OK_RESIDUAL
class DumpColors:
""" Class holding ANSI colors for colorization of hexdump output """
def __init__(self):
self.colors = {'BLUE': '\033[94m',
'GREEN': '\033[92m',
'RESET': '\033[0m',
}
self.enabled = True
return None
def get(self, what):
"""
Get the ANSI code for 'what'
Returns an empty string if disabled/not found
"""
if self.enabled:
if what in self.colors:
return self.colors[what]
return ''
def enable(self):
""" Enable colorization """
self.enabled = True
def disable(self):
""" Disable colorization """
self.enabled = False
def hexdump(src, length=8, colorize=False):
""" Produce a string hexdump of src, for debug output.
Input: bytestring; output: text string
"""
if not src:
return str(src)
if type(src) is not bytes:
raise yubico_exception.InputError('Hexdump \'src\' must be bytestring (got %s)' % type(src))
offset = 0
result = ''
for this in group(src, length):
if colorize:
last, this = this[-1], this[:-1]
colors = DumpColors()
color = colors.get('RESET')
if ord_byte(last) & yubikey_defs.RESP_PENDING_FLAG:
# write to key
color = colors.get('BLUE')
elif ord_byte(last) & yubikey_defs.SLOT_WRITE_FLAG:
color = colors.get('GREEN')
hex_s = color + ' '.join(["%02x" % ord_byte(x) for x in this]) + colors.get('RESET')
hex_s += " %02x" % ord_byte(last)
else:
hex_s = ' '.join(["%02x" % ord_byte(x) for x in this])
result += "%04X %s\n" % (offset, hex_s)
offset += length
return result
def group(data, num):
""" Split data into chunks of num chars each """
return [data[i:i+num] for i in range(0, len(data), num)]
def modhex_decode(data):
""" Convert a modhex bytestring to ordinary hex. """
try:
maketrans = string.maketrans
except AttributeError:
# Python 3
maketrans = bytes.maketrans
t_map = maketrans(b"cbdefghijklnrtuv", b"0123456789abcdef")
return data.translate(t_map)
def hotp_truncate(hmac_result, length=6):
""" Perform the HOTP Algorithm truncating.
Input is a bytestring.
"""
if len(hmac_result) != 20:
raise yubico_exception.YubicoError("HMAC-SHA-1 not 20 bytes long")
offset = ord_byte(hmac_result[19]) & 0xf
bin_code = (ord_byte(hmac_result[offset]) & 0x7f) << 24 \
| (ord_byte(hmac_result[offset+1]) & 0xff) << 16 \
| (ord_byte(hmac_result[offset+2]) & 0xff) << 8 \
| (ord_byte(hmac_result[offset+3]) & 0xff)
return bin_code % (10 ** length)
def tlv_parse(data):
""" Parses a bytestring of TLV values into a dict with the tags as keys."""
parsed = {}
while data:
t, l, data = ord_byte(data[0]), ord_byte(data[1]), data[2:]
parsed[t], data = data[:l], data[l:]
return parsed
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