# -*- test-case-name: twisted.test.test_digestauth -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Calculations for HTTP Digest authentication.

@see: U{http://www.faqs.org/rfcs/rfc2617.html}
"""

from hashlib import md5, sha1



# The digest math

algorithms = {
'md5': md5,

# md5-sess is more complicated than just another algorithm. It requires
# H(A1) state to be remembered from the first WWW-Authenticate challenge
# issued and re-used to process any Authorization header in response to
# that WWW-Authenticate challenge. It is *not* correct to simply
# recalculate H(A1) each time an Authorization header is received. Read
# RFC 2617, section 3.2.2.2 and do not try to make DigestCredentialFactory
# support this unless you completely understand it. -exarkun
'md5-sess': md5,

'sha': sha1,
}

# DigestCalcHA1
def calcHA1(pszAlg, pszUserName, pszRealm, pszPassword, pszNonce, pszCNonce,
preHA1=None):
"""
Compute H(A1) from RFC 2617.

@param pszAlg: The name of the algorithm to use to calculate the digest.
Currently supported are md5, md5-sess, and sha.
@param pszUserName: The username
@param pszRealm: The realm
@param pszPassword: The password
@param pszNonce: The nonce
@param pszCNonce: The cnonce

@param preHA1: If available this is a str containing a previously
calculated H(A1) as a hex string. If this is given then the values for
pszUserName, pszRealm, and pszPassword must be C{None} and are ignored.
"""

if (preHA1 and (pszUserName or pszRealm or pszPassword)):
raise TypeError(("preHA1 is incompatible with the pszUserName, "
"pszRealm, and pszPassword arguments"))

if preHA1 is None:
# We need to calculate the HA1 from the username:realm:password
m = algorithms[pszAlg]()
m.update(pszUserName)
m.update(":")
m.update(pszRealm)
m.update(":")
m.update(pszPassword)
HA1 = m.digest()
else:
# We were given a username:realm:password
HA1 = preHA1.decode('hex')

if pszAlg == "md5-sess":
m = algorithms[pszAlg]()
m.update(HA1)
m.update(":")
m.update(pszNonce)
m.update(":")
m.update(pszCNonce)
HA1 = m.digest()

return HA1.encode('hex')


def calcHA2(algo, pszMethod, pszDigestUri, pszQop, pszHEntity):
"""
Compute H(A2) from RFC 2617.

@param pszAlg: The name of the algorithm to use to calculate the digest.
Currently supported are md5, md5-sess, and sha.
@param pszMethod: The request method.
@param pszDigestUri: The request URI.
@param pszQop: The Quality-of-Protection value.
@param pszHEntity: The hash of the entity body or C{None} if C{pszQop} is
not C{'auth-int'}.
@return: The hash of the A2 value for the calculation of the response
digest.
"""
m = algorithms[algo]()
m.update(pszMethod)
m.update(":")
m.update(pszDigestUri)
if pszQop == "auth-int":
m.update(":")
m.update(pszHEntity)
return m.digest().encode('hex')


def calcResponse(HA1, HA2, algo, pszNonce, pszNonceCount, pszCNonce, pszQop):
"""
Compute the digest for the given parameters.

@param HA1: The H(A1) value, as computed by L{calcHA1}.
@param HA2: The H(A2) value, as computed by L{calcHA2}.
@param pszNonce: The challenge nonce.
@param pszNonceCount: The (client) nonce count value for this response.
@param pszCNonce: The client nonce.
@param pszQop: The Quality-of-Protection value.
"""
m = algorithms[algo]()
m.update(HA1)
m.update(":")
m.update(pszNonce)
m.update(":")
if pszNonceCount and pszCNonce:
m.update(pszNonceCount)
m.update(":")
m.update(pszCNonce)
m.update(":")
m.update(pszQop)
m.update(":")
m.update(HA2)
respHash = m.digest().encode('hex')
return respHash