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verify the mac even if the padding is 1 byte long #234

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merged 1 commit into from
Mar 30, 2018
Merged

verify the mac even if the padding is 1 byte long #234

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2 changes: 1 addition & 1 deletion tlslite/utils/constanttime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -170,7 +170,7 @@ def ct_check_cbc_mac_and_pad(data, mac, seqnumBytes, contentType, version):
data_mac.update(compatHMAC(data[:start_pos]))

# don't check past the array end (already checked to be >= zero)
end_pos = data_len - 1 - mac.digest_size
end_pos = data_len - mac.digest_size

# calculate all possible
for i in range(start_pos, end_pos): # constant for given overall length
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21 changes: 21 additions & 0 deletions unit_tests/test_tlslite_utils_constanttime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@
from hypothesis import given, example
import hypothesis.strategies as st
from tlslite.utils.compat import compatHMAC
from tlslite.utils.cryptomath import getRandomBytes
from tlslite.recordlayer import RecordLayer
import tlslite.utils.tlshashlib as hashlib
import hmac
Expand Down Expand Up @@ -266,6 +267,26 @@ def test_with_invalid_hash(self):
self.assertFalse(ct_check_cbc_mac_and_pad(data, h, seqnum_bytes,
content_type, version))

@given(i=st.integers(1, 20))
def test_with_invalid_random_hash(self, i):
key = compatHMAC(getRandomBytes(20))
seqnum_bytes = bytearray(16)
content_type = 0x15
version = (3, 3)
application_data = getRandomBytes(63)
mac = hashlib.sha1

data = self.data_prepare(application_data, seqnum_bytes, content_type,
version, mac, key)
data[-i] ^= 0xff
padding = bytearray(b'\x00')
data += padding

h = hmac.new(key, digestmod=mac)
h.block_size = mac().block_size
self.assertFalse(ct_check_cbc_mac_and_pad(data, h, seqnum_bytes,
content_type, version))

def test_with_invalid_pad(self):
key = compatHMAC(bytearray(20))
seqnum_bytes = bytearray(16)
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