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* added testing stuff

* Revert "added testing stuff"

This reverts commit 1b102e5.

* added testing stuff

* add printing in gssapi unwrap

* modified calls to AES-CTS encrypt function

* additional printing

* better printing using hexdump

* test.py now has a working example. Take encrypted DsBindResponse from dcshadow wireshark decrypt it, and produces again same encrypted stuff with same signature by taking the padding bytes and the confounder from the encrypted message

* added some logs

* updating gssapi and crypto for aes-cts wrap, unwrap, encryp, decrypt

* last changes for tonight

* some updates

* ncchanges baby!

* reverting change on getMIC

* reverting change on kerberosv5.py

* reverting change on kerberosv5.py

* reverting change on kerberosv5.py

* reverting change on kerberosv5.py

---------

Co-authored-by: MrAle98 <ale18109800@gmail.com>
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@ShutdownRepo @MrAle98
ShutdownRepo and MrAle98 authored Mar 19, 2024
1 parent 93b7533 commit 7bd6762
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34 changes: 25 additions & 9 deletions impacket/krb5/crypto.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@
from binascii import unhexlify
from functools import reduce
from os import urandom

# XXX current status:
# * Done and tested
# - AES encryption, checksum, string2key, prf
Expand All @@ -60,7 +61,6 @@
from Cryptodome.Util.number import GCD as gcd
from six import b, PY3, indexbytes, binary_type


def get_random_bytes(lenBytes):
# We don't really need super strong randomness here to use PyCrypto.Random
return urandom(lenBytes)
Expand Down Expand Up @@ -210,17 +210,23 @@ def derive(cls, key, constant):
return cls.random_to_key(rndseed[0:cls.seedsize])

@classmethod
def encrypt(cls, key, keyusage, plaintext, confounder):
def encrypt(cls, key, keyusage, plaintext, confounder, integrity_blob=None):
ki = cls.derive(key, pack('>IB', keyusage, 0x55))
ke = cls.derive(key, pack('>IB', keyusage, 0xAA))
if confounder is None:
confounder = get_random_bytes(cls.blocksize)
basic_plaintext = confounder + _zeropad(plaintext, cls.padsize)
hmac = HMAC.new(ki.contents, basic_plaintext, cls.hashmod).digest()
return cls.basic_encrypt(ke, basic_plaintext) + hmac[:cls.macsize]
# For Kerberos SSP: blob for HMAC calculation is different from blob for encryption.
# This is undocumented, and was identified by reversing cryptodll.dll
if integrity_blob is not None:
hmac = HMAC.new(ki.contents, integrity_blob, cls.hashmod).digest()
else:
hmac = HMAC.new(ki.contents, basic_plaintext, cls.hashmod).digest()
enc = cls.basic_encrypt(ke, basic_plaintext) + hmac[:cls.macsize]
return enc

@classmethod
def decrypt(cls, key, keyusage, ciphertext):
def decrypt(cls, key, keyusage, ciphertext, ignore_integrity=False, wrap_token_len=None, filler_len=None, dce_rpc_header=None, auth_data_header=None):
ki = cls.derive(key, pack('>IB', keyusage, 0x55))
ke = cls.derive(key, pack('>IB', keyusage, 0xAA))
if len(ciphertext) < cls.blocksize + cls.macsize:
Expand All @@ -229,12 +235,22 @@ def decrypt(cls, key, keyusage, ciphertext):
if len(basic_ctext) % cls.padsize != 0:
raise ValueError('ciphertext does not meet padding requirement')
basic_plaintext = cls.basic_decrypt(ke, bytes(basic_ctext))
hmac = bytearray(HMAC.new(ki.contents, basic_plaintext, cls.hashmod).digest())
plaintext, confounder = bytes(basic_plaintext[cls.blocksize:]), bytes(basic_plaintext[:cls.blocksize])
# For Kerberos SSP: blob for HMAC calculation is different from blob for encryption.
# This is undocumented, and was identified by reversing cryptodll.dll
# in that case, integrity_blob to send to HMAC
# = confounder + dce_rpc_header + data + auth_data_header + filler + wrap_token
# no need to implement, assuming the other client is legit
if dce_rpc_header is not None and auth_data_header is not None:
plaintext_data, plaintext_filler_and_wrap_token_header = plaintext[:-filler_len-wrap_token_len], plaintext[-filler_len-wrap_token_len:] # FIXME dynamically set the filler size
integrity_blob = confounder + dce_rpc_header + plaintext_data + auth_data_header + plaintext_filler_and_wrap_token_header
hmac = bytearray(HMAC.new(ki.contents, integrity_blob, SHA).digest())
else:
hmac = bytearray(HMAC.new(ki.contents, basic_plaintext, SHA).digest())
expmac = hmac[:cls.macsize]
if not _mac_equal(mac, expmac):
if not _mac_equal(mac, expmac) and not ignore_integrity:
raise InvalidChecksum('ciphertext integrity failure')
# Discard the confounder.
return bytes(basic_plaintext[cls.blocksize:])
return bytes(basic_plaintext[cls.blocksize:]), bytes(basic_plaintext[:cls.blocksize])

@classmethod
def prf(cls, key, string):
Expand Down
71 changes: 54 additions & 17 deletions impacket/krb5/gssapi.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
import struct
import random
import string

from six import b

from Cryptodome.Hash import HMAC, MD5
Expand Down Expand Up @@ -123,7 +124,7 @@ def GSS_GetMIC(self, sessionKey, data, sequenceNumber, direction = 'init'):
finalData = GSS_GETMIC_HEADER + token.getData()
return finalData

def GSS_Wrap(self, sessionKey, data, sequenceNumber, direction = 'init', encrypt=True, authData=None):
def GSS_Wrap(self, sessionKey, data, sequenceNumber, direction='init', encrypt=True, authData=None):
# Damn inacurate RFC, useful info from here
# https://social.msdn.microsoft.com/Forums/en-US/fb98e8f4-e697-4652-bcb7-604e027e14cc/gsswrap-token-size-kerberos-and-rc4hmac?forum=os_windowsprotocols
# and here
Expand Down Expand Up @@ -246,27 +247,50 @@ def unrotate(self, data, numBytes):
numBytes %= len(data)
result = data[numBytes:] + data[:numBytes]
return result

def get_filler(self, data):
cipher = self.cipherType()
length = (cipher.blocksize - (len(data) % cipher.blocksize)) or 16
filler = b'\x00' * length
return filler


def GSS_Wrap(self, sessionKey, data, sequenceNumber, direction = 'init', encrypt=True):
def GSS_Wrap(self, sessionKey, data, sequenceNumber, direction='init', encrypt=True, acceptorSubkey=False, keyUsage=KG_USAGE_INITIATOR_SEAL, confounder=None, dce_rpc_header=None, auth_data_header=None):
token = self.WRAP()

cipher = self.cipherType()

# Let's pad the data
pad = (cipher.blocksize - (len(data) % cipher.blocksize)) & 15
padStr = b'\xFF' * pad
data += padStr
if confounder is None:
confounder = b(''.join([rand.choice(string.ascii_letters) for _ in range(16)]))

# The RRC field ([RFC4121] section 4.2.5) is 12 if no encryption is requested or 28 if encryption
# The RRC field ([RFC4121] section 4.2.5) is 12 if no encryption is requested or 28 if encryption
# is requested. The RRC field is chosen such that all the data can be encrypted in place.
rrc = 28

token['Flags'] = 6
token['EC'] = pad
token['Flags'] = 0
if acceptorSubkey:
token['Flags'] |= 4 # AcceptorSubKey flag (0x00100)
if encrypt:
token['Flags'] |= 2 # Sealed flag (0x00010)
if direction != 'init':
token['Flags'] |= 1 # SendByAcceptor flag (0x00001)

token['EC'] = len(self.get_filler(data))
# (RFC4121 section 4.2.4) the RRC field (as
# defined in section 4.2.5) in the to-be-encrypted header contains the
# hex value 00 00.
token['RRC'] = 0
token['SND_SEQ'] = struct.pack('>Q',sequenceNumber)
token['SND_SEQ'] = struct.pack('>Q', sequenceNumber)

# For Kerberos SSP: blob for HMAC calculation is different from blob for encryption.
# This is undocumented, and was identified by reversing cryptodll.dll
integrity_blob = None
if dce_rpc_header is not None and auth_data_header is not None:
integrity_blob = confounder + dce_rpc_header + data + auth_data_header + self.get_filler(data) + token.getData()

cipherText = cipher.encrypt(sessionKey, KG_USAGE_INITIATOR_SEAL, data + token.getData(), None)
data += self.get_filler(data)

cipherText = cipher.encrypt(key=sessionKey, keyusage=keyUsage, plaintext=data + token.getData(), confounder=confounder, integrity_blob=integrity_blob)
token['RRC'] = rrc

cipherText = self.rotate(cipherText, token['RRC'] + token['EC'])
Expand All @@ -277,18 +301,31 @@ def GSS_Wrap(self, sessionKey, data, sequenceNumber, direction = 'init', encrypt

return ret1, ret2

def GSS_Unwrap(self, sessionKey, data, sequenceNumber, direction = 'init', encrypt=True, authData=None):
def GSS_Unwrap(self, sessionKey, data, sequenceNumber, direction='init', encrypt=True, authData=None, keyUsage=KG_USAGE_ACCEPTOR_SEAL, dce_rpc_header=None, auth_data_header=None, ignore_integrity=False):
# implementation as per [MS-KILE] Section 4.3
from impacket.dcerpc.v5.rpcrt import SEC_TRAILER

cipher = self.cipherType()
token = self.WRAP(authData[len(SEC_TRAILER()):])

rotated = authData[len(self.WRAP())+len(SEC_TRAILER()):] + data

cipherText = self.unrotate(rotated, token['RRC'] + token['EC'])
plainText = cipher.decrypt(sessionKey, KG_USAGE_ACCEPTOR_SEAL, cipherText)
enc1 = authData[len(self.WRAP()) + len(SEC_TRAILER()):]
enc2 = data

cipherText = self.unrotate(enc1 + enc2, token['RRC'] + token['EC'])

# For Kerberos SSP: blob for HMAC calculation is different from blob for encryption.
# This is undocumented, and was identified by reversing cryptodll.dll
# no need to implement, assuming the other client is legit
plainText, confounder = cipher.decrypt(
sessionKey, keyUsage, cipherText,
dce_rpc_header=dce_rpc_header, auth_data_header=auth_data_header, ignore_integrity=ignore_integrity,
wrap_token_len=len(self.WRAP()), filler_len=token['EC']
)

encdata, enchdr = plainText[:-len(self.WRAP())], plainText[-len(self.WRAP()):]
encdata, filler = encdata[:-token['EC']], encdata[-token['EC']:]

return plainText[:-(token['EC']+len(self.WRAP()))], None
return encdata, confounder

class GSSAPI_AES256(GSSAPI_AES):
checkSumProfile = crypto._SHA1AES256
Expand Down

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