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"""
Implementation of `modhex encoding <http://www.yubico.com/modhex-calculator>`_,
which uses keyboard-independent characters.
::
hex digit: 0123456789abcdef
modhex digit: cbdefghijklnrtuv
"""
from binascii import hexlify, unhexlify
from functools import partial
import struct
__all__ = ['modhex', 'unmodhex', 'is_modhex', 'hex_to_modhex', 'modhex_to_hex']
def modhex(data):
"""
Encode a string of bytes as modhex.
>>> modhex(b'abcdefghijklmnop') == b'hbhdhehfhghhhihjhkhlhnhrhthuhvic'
True
"""
return hex_to_modhex(hexlify(data))
def unmodhex(encoded):
"""
Decode a modhex string to its binary form.
>>> unmodhex(b'hbhdhehfhghhhihjhkhlhnhrhthuhvic') == b'abcdefghijklmnop'
True
"""
return unhexlify(modhex_to_hex(encoded))
def is_modhex(encoded):
"""
Returns ``True`` iff the given string is valid modhex.
>>> is_modhex(b'cbdefghijklnrtuv')
True
>>> is_modhex(b'cbdefghijklnrtuvv')
False
>>> is_modhex(b'cbdefghijklnrtuvyy')
False
"""
if any(c not in modhex_chars for c in encoded):
return False
elif len(encoded) % 2 != 0:
return False
else:
return True
def hex_to_modhex(hex_str):
"""
Convert a string of hex digits to a string of modhex digits.
>>> hex_to_modhex(b'69b6481c8baba2b60e8f22179b58cd56') == b'hknhfjbrjnlnldnhcujvddbikngjrtgh'
True
>>> hex_to_modhex(b'6j')
Traceback (most recent call last):
...
ValueError: Illegal hex character in input
"""
try:
return b''.join(int2byte(hex_to_modhex_char(b))
for b in iter(hex_str.lower()))
except ValueError:
raise ValueError('Illegal hex character in input')
def modhex_to_hex(modhex_str):
"""
Convert a string of modhex digits to a string of hex digits.
>>> modhex_to_hex(b'hknhfjbrjnlnldnhcujvddbikngjrtgh') == b'69b6481c8baba2b60e8f22179b58cd56'
True
>>> modhex_to_hex(b'hbhdxx')
Traceback (most recent call last):
...
ValueError: Illegal modhex character in input
"""
try:
return b''.join(int2byte(modhex_to_hex_char(b))
for b in iter(modhex_str.lower()))
except ValueError:
raise ValueError('Illegal modhex character in input')
#
# Internals
#
def int2byte(i):
return struct.Struct(">B").pack(i)
def lookup(alist, key):
try:
return next(v for (k, v) in alist if k == key)
except StopIteration:
raise ValueError()
hex_chars = b'0123456789abcdef'
modhex_chars = b'cbdefghijklnrtuv'
hex_to_modhex_map = list(zip(iter(hex_chars), iter(modhex_chars)))
modhex_to_hex_map = list(zip(iter(modhex_chars), iter(hex_chars)))
hex_to_modhex_char = partial(lookup, hex_to_modhex_map)
modhex_to_hex_char = partial(lookup, modhex_to_hex_map)
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