simpletotp / src / simpletotp / __init__.py

#!/usr/bin/env python
"""
OATH HOTP + TOTP Implementation in python.
 
Based on http://tools.ietf.org/html/rfc4226
 
Parameter and function names kept inline with the RFC
(e.g. HOTP, Truncate, K, C etc)
"""
 
import hmac
import hashlib
import array
import time
 
def HOTP(K, C, digits=6):
    """
    HOTP accepts key K and counter C
    optional digits parameter can control the response length
 
    returns the OATH integer code with {digits} length
    """
    C_bytes = _long_to_byte_array(C)
    hmac_sha1 = hmac.new(key=K, msg=C_bytes,
                         digestmod=hashlib.sha1).hexdigest()
    return Truncate(hmac_sha1)[-digits:]
 
def TOTP(K, digits=6, window=30):
    """
    TOTP is a time-based variant of HOTP.
    It accepts only key K, since the counter is derived from the current time
    optional digits parameter can control the response length
    optional window parameter controls the time window in seconds
 
    returns the OATH integer code with {digits} length
    """
    C = long(time.time() / window)
    return HOTP(K, C, digits=digits)
 
def Truncate(hmac_sha1):
    """
    Truncate represents the function that converts an HMAC-SHA-1
    value into an HOTP value as defined in Section 5.3.
 
http://tools.ietf.org/html/rfc4226#section-5.3
 
    """
    offset = int(hmac_sha1[-1], 16)
    binary = int(hmac_sha1[(offset * 2):((offset * 2) + 8)], 16) & 0x7fffffff
    return str(binary)
 
def _long_to_byte_array(long_num):
    """
    helper function to convert a long number into a byte array
    """
    byte_array = array.array('B')
    for i in reversed(range(0, 8)):
        byte_array.insert(0, long_num & 0xff)
        long_num >>= 8
    return byte_array
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