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# -*- coding: utf-8 -*-
"""
# HOTP/TOTP support
# Copyright (c) 2019 Michael Buesch <m@bues.ch>
# Licensed under the GNU/GPL version 2 or later.
"""
import time
from base64 import b32decode
import binascii
import hmac
import hashlib
__all__ = [
"OtpError",
"hotp",
"totp",
]
class OtpError(Exception):
pass
def hotp(key, counter, nrDigits=6, hmacHash="SHA1"):
"""HOTP: An HMAC-Based One-Time Password Algorithm.
"""
if isinstance(key, str):
try:
key = b32decode(key.encode("UTF-8"), casefold=True)
except (binascii.Error, UnicodeError):
raise OtpError("Invalid key.")
if not (0 <= counter <= (2 ** 64) - 1):
raise OtpError("Invalid counter.")
if not (1 <= nrDigits <= 8):
raise OtpError("Invalid number of digits.")
try:
{
"SHA1" : hashlib.sha1,
"SHA256" : hashlib.sha256,
"SHA512" : hashlib.sha512,
}[hmacHash.upper().strip()]
except KeyError:
raise OtpError("Invalid HMAC hash type.")
counter = bytes(((counter >> 56) & 0xFF,
(counter >> 48) & 0xFF,
(counter >> 40) & 0xFF,
(counter >> 32) & 0xFF,
(counter >> 24) & 0xFF,
(counter >> 16) & 0xFF,
(counter >> 8) & 0xFF,
(counter >> 0) & 0xFF))
h = hmac.new(key, counter, hmacHash).digest()
offset = h[19] & 0xF
hSlice = (((h[offset + 0] & 0x7F) << 24) |
((h[offset + 1] & 0xFF) << 16) |
((h[offset + 2] & 0xFF) << 8) |
((h[offset + 3] & 0xFF) << 0))
otp = hSlice % (10 ** nrDigits)
fmt = "%0" + str(nrDigits) + "d"
return fmt % otp
def totp(key, nrDigits=6, hmacHash="SHA1", t=None):
"""TOTP: Time-Based One-Time Password Algorithm.
"""
if t is None:
t = time.time()
t = (int(round(t)) // 30) - 1
return hotp(key, t, nrDigits, hmacHash)
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