def checkOtp(self, otpVal, counter=None, window=None, options=None):
"""
checkOtp - validate the token otp against a given otpvalue
:param otpVal: the to be verified otpvalue
:type otpVal: string
:param counter: the counter state. It is not used by the YubiKey because the current counter value
is sent encrypted inside the OTP value
:type counter: int
:param window: the counter +window, which is not used in the YubiKey because the current
counter value is sent encrypted inside the OTP, allowing a simple comparison between the encrypted
counter value and the stored counter value
:type window: int
:param options: the dict, which could contain token specific info
:type options: dict
:return: the counter state or an error code (< 0):
-1 if the OTP is old (counter < stored counter)
-2 if the private_uid sent in the OTP is wrong (different from the one stored with the token)
-3 if the CRC verification fails
:rtype: int
From: http://www.yubico.com/wp-content/uploads/2013/04/YubiKey-Manual-v3_1.pdf
6 Implementation details
"""
res = -1
if len(otpVal) < self.getOtpLen():
return res
serial = self.token.getSerial()
secObj = self._get_secret_object()
anOtpVal = otpVal.lower()
# The prefix is the characters in front of the last 32 chars
# We can also check the PREFIX! At the moment, we do not use it!
yubi_prefix = anOtpVal[:-32]
# verify the prefix if any
enroll_prefix = self.getFromTokenInfo('public_uid', None)
if enroll_prefix and enroll_prefix != yubi_prefix:
return res
# The variable otp val is the last 32 chars
yubi_otp = anOtpVal[-32:]
try:
otp_bin = modhex_decode(yubi_otp)
msg_bin = secObj.aes_decrypt(otp_bin)
except KeyError:
log.warning("failed to decode yubi_otp!")
return res
msg_hex = binascii.hexlify(msg_bin)
uid = msg_hex[0:12]
log.debug("[checkOtp] uid: %r" % uid)
log.debug("[checkOtp] prefix: %r" %
binascii.hexlify(modhex_decode(yubi_prefix)))
# usage_counter can go from 1 – 0x7fff
usage_counter = msg_hex[12:16]
# TODO: We also could check the timestamp
# - the timestamp. see http://www.yubico.com/wp-content/uploads/2013/04/YubiKey-Manual-v3_1.pdf
timestamp = msg_hex[16:22]
# session counter can go from 00 to 0xff
session_counter = msg_hex[22:24]
random = msg_hex[24:28]
log.debug("[checkOtp] decrypted: usage_count: %r, session_count: %r" %
(usage_counter, session_counter))
# The checksum is a CRC-16 (16-bit ISO 13239 1st complement) that
# occupies the last 2 bytes of the decrypted OTP value. Calculating the
# CRC-16 checksum of the whole decrypted OTP should give a fixed residual
# of 0xf0b8 (see Yubikey-Manual - Chapter 6: Implementation details).
crc = msg_hex[28:]
log.debug("[checkOtp] calculated checksum (61624): %r" %
checksum(msg_hex))
if checksum(msg_hex) != 0xf0b8:
log.warning("[checkOtp] CRC checksum for token %r failed" % serial)
return -3
# create the counter as integer
# Note: The usage counter is stored LSB!
count_hex = usage_counter[2:4] + usage_counter[0:2] + session_counter
count_int = int(count_hex, 16)
log.debug('[checkOtp] decrypted counter: %r' % count_int)
tokenid = self.getFromTokenInfo("yubikey.tokenid")
if not tokenid:
log.debug("[checkOtp] Got no tokenid for %r. Setting to %r." %
(serial, uid))
tokenid = uid
self.addToTokenInfo("yubikey.tokenid", tokenid)
if tokenid != uid:
# wrong token!
log.warning(
"[checkOtp] The wrong token was presented for %r. Got %r, expected %r."
% (serial, uid, tokenid))
return -2
log.debug('[checkOtp] compare counter to LinOtpCount: %r' %
self.token.LinOtpCount)
if count_int >= self.token.LinOtpCount:
res = count_int
return res
def checkOtp(self, otpVal, counter=None, window=None, options=None):
"""
checkOtp - validate the token otp against a given otpvalue
:param otpVal: the to be verified otpvalue
:type otpVal: string
:param counter: the counter state. It is not used by the YubiKey because the current counter value
is sent encrypted inside the OTP value
:type counter: int
:param window: the counter +window, which is not used in the YubiKey because the current
counter value is sent encrypted inside the OTP, allowing a simple comparison between the encrypted
counter value and the stored counter value
:type window: int
:param options: the dict, which could contain token specific info
:type options: dict
:return: the counter state or an error code (< 0):
-1 if the OTP is old (counter < stored counter)
-2 if the private_uid sent in the OTP is wrong (different from the one stored with the token)
-3 if the CRC verification fails
:rtype: int
From: http://www.yubico.com/wp-content/uploads/2013/04/YubiKey-Manual-v3_1.pdf
6 Implementation details
"""
log.debug("[checkOtp] begin. Validate the token otp: otpVal: %r, counter: %r, options: %r "
% (otpVal, counter, options))
res = -1
if len(otpVal) < self.getOtpLen():
return res
serial = self.token.getSerial()
secObj = self._get_secret_object()
anOtpVal = otpVal.lower()
# The prefix is the characters in front of the last 32 chars
# We can also check the PREFIX! At the moment, we do not use it!
yubi_prefix = anOtpVal[:-32]
# verify the prefix if any
enroll_prefix = self.getFromTokenInfo('public_uid', None)
if enroll_prefix and enroll_prefix != yubi_prefix:
return res
# The variable otp val is the last 32 chars
yubi_otp = anOtpVal[-32:]
try:
otp_bin = modhex_decode(yubi_otp)
msg_bin = secObj.aes_decrypt(otp_bin)
except KeyError:
log.warning("failed to decode yubi_otp!")
return res
msg_hex = binascii.hexlify(msg_bin)
uid = msg_hex[0:12]
log.debug("[checkOtp] uid: %r" % uid)
log.debug("[checkOtp] prefix: %r" % binascii.hexlify(modhex_decode(yubi_prefix)))
# usage_counter can go from 1 – 0x7fff
usage_counter = msg_hex[12:16]
# TODO: We also could check the timestamp
# - the timestamp. see http://www.yubico.com/wp-content/uploads/2013/04/YubiKey-Manual-v3_1.pdf
timestamp = msg_hex[16:22]
# session counter can go from 00 to 0xff
session_counter = msg_hex[22:24]
random = msg_hex[24:28]
log.debug("[checkOtp] decrypted: usage_count: %r, session_count: %r"
% (usage_counter, session_counter))
# The checksum is a CRC-16 (16-bit ISO 13239 1st complement) that
# occupies the last 2 bytes of the decrypted OTP value. Calculating the
# CRC-16 checksum of the whole decrypted OTP should give a fixed residual
# of 0xf0b8 (see Yubikey-Manual - Chapter 6: Implementation details).
crc = msg_hex[28:]
log.debug("[checkOtp] calculated checksum (61624): %r" % checksum(msg_hex))
if checksum(msg_hex) != 0xf0b8:
log.warning("[checkOtp] CRC checksum for token %r failed" % serial)
return -3
# create the counter as integer
# Note: The usage counter is stored LSB!
count_hex = usage_counter[2:4] + usage_counter[0:2] + session_counter
count_int = int(count_hex, 16)
log.debug('[checkOtp] decrypted counter: %r' % count_int)
tokenid = self.getFromTokenInfo("yubikey.tokenid")
if not tokenid:
log.debug("[checkOtp] Got no tokenid for %r. Setting to %r." % (serial, uid))
tokenid = uid
self.addToTokenInfo("yubikey.tokenid", tokenid)
if tokenid != uid:
# wrong token!
log.warning("[checkOtp] The wrong token was presented for %r. Got %r, expected %r."
% (serial, uid, tokenid))
return -2
log.debug('[checkOtp] compare counter to LinOtpCount: %r' % self.token.LinOtpCount)
if count_int >= self.token.LinOtpCount:
res = count_int
return res