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Don't exercise OAEP with small key and large hash

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RSA-OAEP requires the key to be larger than a function of the hash size.
Ideally such combinations would be detected as a key/algorithm
incompatibility. However key/algorithm compatibility is currently tested
between the key type and the algorithm without considering the key size, and
this is inconvenient to change. So as a workaround, dispense
OAEP-with-too-small-hash from exercising, without including it in the
automatic operation-failure test generation.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2022-03-19 12:09:13 +01:00
parent d586b82e12
commit 4bd90dc6b1
2 changed files with 51 additions and 11 deletions
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33
scripts/mbedtls_dev/crypto_knowledge.py
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@ -213,7 +213,7 @@ class KeyType:
This function does not currently handle key derivation or PAKE.
"""
#pylint: disable=too-many-return-statements
#pylint: disable=too-many-branches,too-many-return-statements
if alg.is_wildcard:
return False
if alg.is_invalid_truncation():
@ -425,28 +425,41 @@ class Algorithm:
"""
return short_expression(self.expression, level=level)
HASH_LENGTH = {
'PSA_ALG_MD5': 16,
'PSA_ALG_SHA_1': 20,
}
HASH_LENGTH_BITS_RE = re.compile(r'([0-9]+)\Z')
@classmethod
def hash_length(cls, alg: str) -> int:
"""The length of the given hash algorithm, in bytes."""
if alg in cls.HASH_LENGTH:
return cls.HASH_LENGTH[alg]
m = cls.HASH_LENGTH_BITS_RE.search(alg)
if m:
return int(m.group(1)) // 8
raise ValueError('Unknown hash length for ' + alg)
PERMITTED_TAG_LENGTHS = {
'PSA_ALG_CCM': frozenset([4, 6, 8, 10, 12, 14, 16]),
'PSA_ALG_CHACHA20_POLY1305': frozenset([16]),
'PSA_ALG_GCM': frozenset([4, 8, 12, 13, 14, 15, 16]),
}
MAC_LENGTH = {
'PSA_ALG_CBC_MAC': 16,
'PSA_ALG_CMAC': 16,
'PSA_ALG_HMAC(PSA_ALG_MD5)': 16,
'PSA_ALG_HMAC(PSA_ALG_SHA_1)': 20,
'PSA_ALG_CBC_MAC': 16, # actually the block cipher length
'PSA_ALG_CMAC': 16, # actually the block cipher length
}
HMAC_WITH_NOMINAL_LENGTH_RE = re.compile(r'PSA_ALG_HMAC\(\w+([0-9])+\)\Z')
HMAC_RE = re.compile(r'PSA_ALG_HMAC\((.*)\)\Z')
@classmethod
def mac_or_tag_length(cls, base: str) -> FrozenSet[int]:
def mac_or_tag_lengths(cls, base: str) -> FrozenSet[int]:
"""Return the set of permitted lengths for the given MAC or AEAD tag."""
if base in cls.PERMITTED_TAG_LENGTHS:
return cls.PERMITTED_TAG_LENGTHS[base]
max_length = cls.MAC_LENGTH.get(base, None)
if max_length is None:
m = cls.HMAC_WITH_NOMINAL_LENGTH_RE.match(base)
m = cls.HMAC_RE.match(base)
if m:
max_length = int(m.group(1)) // 8
max_length = cls.hash_length(m.group(1))
if max_length is None:
raise ValueError('Unknown permitted lengths for ' + base)
return frozenset(range(4, max_length + 1))
@ -466,7 +479,7 @@ class Algorithm:
if m:
base = m.group('base')
to_length = int(m.group('length'), 0)
permitted_lengths = self.mac_or_tag_length(base)
permitted_lengths = self.mac_or_tag_lengths(base)
if to_length not in permitted_lengths:
return True
return False