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import string, md5
from pysnmp.proto.secmod.rfc3414.auth import base
from pysnmp.proto import error
_twelveZeros = '\x00'*12
_fortyEightZeros = '\x00'*48
# rfc3414: 6.2.4
class HmacMd5(base.AbstractAuthenticationService):
serviceID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 2) # usmHMACMD5AuthProtocol
__ipad = [0x36]*64
__opad = [0x5C]*64
# 6.3.1
def authenticateOutgoingMsg(self, authKey, wholeMsg):
# Here we expect calling secmod to indicate where the digest
# should be in the substrate. Also, it pre-sets digest placeholder
# so we hash wholeMsg out of the box.
# Yes, that's ugly but that's rfc...
l = string.find(wholeMsg, _twelveZeros)
if l == -1:
raise error.ProtocolError('Cant locate digest placeholder')
wholeHead = wholeMsg[:l]
wholeTail = wholeMsg[l+12:]
# 6.3.1.1
# 6.3.1.2a
extendedAuthKey = map(ord, str(authKey) + _fortyEightZeros)
# 6.3.1.2b --> noop
# 6.3.1.2c
k1 = string.join(
map(lambda x,y: chr(x^y), extendedAuthKey, self.__ipad), ''
)
# 6.3.1.2d --> noop
# 6.3.1.2e
k2 = string.join(
map(lambda x,y: chr(x^y), extendedAuthKey, self.__opad), ''
)
# 6.3.1.3
d1 = md5.md5(k1+wholeMsg).digest()
# 6.3.1.4
d2 = md5.md5(k2+d1).digest()
mac = d2[:12]
# 6.3.1.5 & 6
return '%s%s%s' % (wholeHead, mac, wholeTail)
# 6.3.2
def authenticateIncomingMsg(self, authKey, authParameters, wholeMsg):
# 6.3.2.1 & 2
if len(authParameters) != 12:
raise error.StatusInformation(
errorIndication='authenticationError'
)
# 6.3.2.3
l = string.find(wholeMsg, str(authParameters))
if l == -1:
raise error.ProtocolError('Cant locate digest in wholeMsg')
wholeHead = wholeMsg[:l]
wholeTail = wholeMsg[l+12:]
authenticatedWholeMsg = '%s%s%s' % (
wholeHead, _twelveZeros, wholeTail
)
# 6.3.2.4a
extendedAuthKey = map(ord, str(authKey) + _fortyEightZeros)
# 6.3.2.4b --> noop
# 6.3.2.4c
k1 = string.join(
map(lambda x,y: chr(x^y), extendedAuthKey, self.__ipad), ''
)
# 6.3.2.4d --> noop
# 6.3.2.4e
k2 = string.join(
map(lambda x,y: chr(x^y), extendedAuthKey, self.__opad), ''
)
# 6.3.2.5a
d1 = md5.md5(k1+authenticatedWholeMsg).digest()
# 6.3.2.5b
d2 = md5.md5(k2+d1).digest()
# 6.3.2.5c
mac = d2[:12]
# 6.3.2.6
if mac != authParameters:
raise error.StatusInformation(
errorIndication='authenticationFailure'
)
return authenticatedWholeMsg
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