Add knowledge of algorithms
Determine the category of operations supported by an algorithm based on its name. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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Gilles Peskine
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@ -18,11 +18,21 @@ This module is entirely based on the PSA API.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import enum
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import re
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from typing import Dict, Iterable, Optional, Pattern, Tuple
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from mbedtls_dev.asymmetric_key_data import ASYMMETRIC_KEY_DATA
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BLOCK_MAC_MODES = frozenset(['CBC_MAC', 'CMAC'])
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BLOCK_CIPHER_MODES = frozenset([
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'CTR', 'CFB', 'OFB', 'XTS', 'CCM_STAR_NO_TAG',
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'ECB_NO_PADDING', 'CBC_NO_PADDING', 'CBC_PKCS7',
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])
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BLOCK_AEAD_MODES = frozenset(['CCM', 'GCM'])
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class KeyType:
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"""Knowledge about a PSA key type."""
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@ -153,3 +163,144 @@ class KeyType:
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"""
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# This is just temporaly solution for the implicit usage flags.
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return re.match(self.KEY_TYPE_FOR_SIGNATURE[usage], self.name) is not None
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class AlgorithmCategory(enum.Enum):
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"""PSA algorithm categories."""
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# The numbers are aligned with the category bits in numerical values of
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# algorithms.
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HASH = 2
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MAC = 3
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CIPHER = 4
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AEAD = 5
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SIGN = 6
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ASYMMETRIC_ENCRYPTION = 7
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KEY_DERIVATION = 8
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KEY_AGREEMENT = 9
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PAKE = 10
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def requires_key(self) -> bool:
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return self not in {self.HASH, self.KEY_DERIVATION}
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class AlgorithmNotRecognized(Exception):
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def __init__(self, expr: str) -> None:
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super().__init__('Algorithm not recognized: ' + expr)
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self.expr = expr
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class Algorithm:
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"""Knowledge about a PSA algorithm."""
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@staticmethod
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def determine_base(expr: str) -> str:
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"""Return an expression for the "base" of the algorithm.
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This strips off variants of algorithms such as MAC truncation.
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This function does not attempt to detect invalid inputs.
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"""
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m = re.match(r'PSA_ALG_(?:'
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r'(?:TRUNCATED|AT_LEAST_THIS_LENGTH)_MAC|'
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r'AEAD_WITH_(?:SHORTENED|AT_LEAST_THIS_LENGTH)_TAG'
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r')\((.*),[^,]+\)\Z', expr)
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if m:
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expr = m.group(1)
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return expr
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@staticmethod
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def determine_head(expr: str) -> str:
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"""Return the head of an algorithm expression.
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The head is the first (outermost) constructor, without its PSA_ALG_
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prefix, and with some normalization of similar algorithms.
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"""
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m = re.match(r'PSA_ALG_(?:DETERMINISTIC_)?(\w+)', expr)
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if not m:
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raise AlgorithmNotRecognized(expr)
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head = m.group(1)
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if head == 'KEY_AGREEMENT':
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m = re.match(r'PSA_ALG_KEY_AGREEMENT\s*\(\s*PSA_ALG_(\w+)', expr)
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if not m:
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raise AlgorithmNotRecognized(expr)
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head = m.group(1)
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head = re.sub(r'_ANY\Z', r'', head)
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if re.match(r'ED[0-9]+PH\Z', head):
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head = 'EDDSA_PREHASH'
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return head
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CATEGORY_FROM_HEAD = {
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'SHA': AlgorithmCategory.HASH,
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'SHAKE256_512': AlgorithmCategory.HASH,
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'MD': AlgorithmCategory.HASH,
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'RIPEMD': AlgorithmCategory.HASH,
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'ANY_HASH': AlgorithmCategory.HASH,
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'HMAC': AlgorithmCategory.MAC,
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'STREAM_CIPHER': AlgorithmCategory.CIPHER,
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'CHACHA20_POLY1305': AlgorithmCategory.AEAD,
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'DSA': AlgorithmCategory.SIGN,
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'ECDSA': AlgorithmCategory.SIGN,
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'EDDSA': AlgorithmCategory.SIGN,
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'PURE_EDDSA': AlgorithmCategory.SIGN,
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'RSA_PSS': AlgorithmCategory.SIGN,
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'RSA_PKCS1V15_SIGN': AlgorithmCategory.SIGN,
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'RSA_PKCS1V15_CRYPT': AlgorithmCategory.ASYMMETRIC_ENCRYPTION,
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'RSA_OAEP': AlgorithmCategory.ASYMMETRIC_ENCRYPTION,
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'HKDF': AlgorithmCategory.KEY_DERIVATION,
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'TLS12_PRF': AlgorithmCategory.KEY_DERIVATION,
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'TLS12_PSK_TO_MS': AlgorithmCategory.KEY_DERIVATION,
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'PBKDF': AlgorithmCategory.KEY_DERIVATION,
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'ECDH': AlgorithmCategory.KEY_AGREEMENT,
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'FFDH': AlgorithmCategory.KEY_AGREEMENT,
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# KEY_AGREEMENT(...) is a key derivation with a key agreement component
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'KEY_AGREEMENT': AlgorithmCategory.KEY_DERIVATION,
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'JPAKE': AlgorithmCategory.PAKE,
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}
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for x in BLOCK_MAC_MODES:
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CATEGORY_FROM_HEAD[x] = AlgorithmCategory.MAC
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for x in BLOCK_CIPHER_MODES:
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CATEGORY_FROM_HEAD[x] = AlgorithmCategory.CIPHER
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for x in BLOCK_AEAD_MODES:
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CATEGORY_FROM_HEAD[x] = AlgorithmCategory.AEAD
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def determine_category(self, expr: str, head: str) -> AlgorithmCategory:
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"""Return the category of the given algorithm expression.
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This function does not attempt to detect invalid inputs.
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"""
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prefix = head
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while prefix:
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if prefix in self.CATEGORY_FROM_HEAD:
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return self.CATEGORY_FROM_HEAD[prefix]
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if re.match(r'.*[0-9]\Z', prefix):
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prefix = re.sub(r'_*[0-9]+\Z', r'', prefix)
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else:
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prefix = re.sub(r'_*[^_]*\Z', r'', prefix)
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raise AlgorithmNotRecognized(expr)
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@staticmethod
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def determine_wildcard(expr) -> bool:
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"""Whether the given algorithm expression is a wildcard.
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This function does not attempt to detect invalid inputs.
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"""
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if re.search(r'\bPSA_ALG_ANY_HASH\b', expr):
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return True
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if re.search(r'_AT_LEAST_', expr):
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return True
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return False
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def __init__(self, expr: str) -> None:
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"""Analyze an algorithm value.
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The algorithm must be expressed as a C expression containing only
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calls to PSA algorithm constructor macros and numeric literals.
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This class is only programmed to handle valid expressions. Invalid
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expressions may result in exceptions or in nonsensical results.
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"""
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self.expression = re.sub(r'\s+', r'', expr)
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self.base_expression = self.determine_base(self.expression)
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self.head = self.determine_head(self.base_expression)
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self.category = self.determine_category(self.base_expression, self.head)
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self.is_wildcard = self.determine_wildcard(self.expression)
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