From ee7554e606a8be1eac00fca05d336dfccafa5ba3 Mon Sep 17 00:00:00 2001 From: Gilles Peskine Date: Thu, 29 Apr 2021 20:38:01 +0200 Subject: [PATCH] Add knowledge of algorithms Determine the category of operations supported by an algorithm based on its name. Signed-off-by: Gilles Peskine --- scripts/mbedtls_dev/crypto_knowledge.py | 151 ++++++++++++++++++++++++ 1 file changed, 151 insertions(+) diff --git a/scripts/mbedtls_dev/crypto_knowledge.py b/scripts/mbedtls_dev/crypto_knowledge.py index 6b38aac16..072d53d93 100644 --- a/scripts/mbedtls_dev/crypto_knowledge.py +++ b/scripts/mbedtls_dev/crypto_knowledge.py @@ -18,11 +18,21 @@ This module is entirely based on the PSA API. # See the License for the specific language governing permissions and # limitations under the License. +import enum import re from typing import Dict, Iterable, Optional, Pattern, Tuple from mbedtls_dev.asymmetric_key_data import ASYMMETRIC_KEY_DATA + +BLOCK_MAC_MODES = frozenset(['CBC_MAC', 'CMAC']) +BLOCK_CIPHER_MODES = frozenset([ + 'CTR', 'CFB', 'OFB', 'XTS', 'CCM_STAR_NO_TAG', + 'ECB_NO_PADDING', 'CBC_NO_PADDING', 'CBC_PKCS7', +]) +BLOCK_AEAD_MODES = frozenset(['CCM', 'GCM']) + + class KeyType: """Knowledge about a PSA key type.""" @@ -153,3 +163,144 @@ class KeyType: """ # This is just temporaly solution for the implicit usage flags. return re.match(self.KEY_TYPE_FOR_SIGNATURE[usage], self.name) is not None + + +class AlgorithmCategory(enum.Enum): + """PSA algorithm categories.""" + # The numbers are aligned with the category bits in numerical values of + # algorithms. + HASH = 2 + MAC = 3 + CIPHER = 4 + AEAD = 5 + SIGN = 6 + ASYMMETRIC_ENCRYPTION = 7 + KEY_DERIVATION = 8 + KEY_AGREEMENT = 9 + PAKE = 10 + + def requires_key(self) -> bool: + return self not in {self.HASH, self.KEY_DERIVATION} + + +class AlgorithmNotRecognized(Exception): + def __init__(self, expr: str) -> None: + super().__init__('Algorithm not recognized: ' + expr) + self.expr = expr + + +class Algorithm: + """Knowledge about a PSA algorithm.""" + + @staticmethod + def determine_base(expr: str) -> str: + """Return an expression for the "base" of the algorithm. + + This strips off variants of algorithms such as MAC truncation. + + This function does not attempt to detect invalid inputs. + """ + m = re.match(r'PSA_ALG_(?:' + r'(?:TRUNCATED|AT_LEAST_THIS_LENGTH)_MAC|' + r'AEAD_WITH_(?:SHORTENED|AT_LEAST_THIS_LENGTH)_TAG' + r')\((.*),[^,]+\)\Z', expr) + if m: + expr = m.group(1) + return expr + + @staticmethod + def determine_head(expr: str) -> str: + """Return the head of an algorithm expression. + + The head is the first (outermost) constructor, without its PSA_ALG_ + prefix, and with some normalization of similar algorithms. + """ + m = re.match(r'PSA_ALG_(?:DETERMINISTIC_)?(\w+)', expr) + if not m: + raise AlgorithmNotRecognized(expr) + head = m.group(1) + if head == 'KEY_AGREEMENT': + m = re.match(r'PSA_ALG_KEY_AGREEMENT\s*\(\s*PSA_ALG_(\w+)', expr) + if not m: + raise AlgorithmNotRecognized(expr) + head = m.group(1) + head = re.sub(r'_ANY\Z', r'', head) + if re.match(r'ED[0-9]+PH\Z', head): + head = 'EDDSA_PREHASH' + return head + + CATEGORY_FROM_HEAD = { + 'SHA': AlgorithmCategory.HASH, + 'SHAKE256_512': AlgorithmCategory.HASH, + 'MD': AlgorithmCategory.HASH, + 'RIPEMD': AlgorithmCategory.HASH, + 'ANY_HASH': AlgorithmCategory.HASH, + 'HMAC': AlgorithmCategory.MAC, + 'STREAM_CIPHER': AlgorithmCategory.CIPHER, + 'CHACHA20_POLY1305': AlgorithmCategory.AEAD, + 'DSA': AlgorithmCategory.SIGN, + 'ECDSA': AlgorithmCategory.SIGN, + 'EDDSA': AlgorithmCategory.SIGN, + 'PURE_EDDSA': AlgorithmCategory.SIGN, + 'RSA_PSS': AlgorithmCategory.SIGN, + 'RSA_PKCS1V15_SIGN': AlgorithmCategory.SIGN, + 'RSA_PKCS1V15_CRYPT': AlgorithmCategory.ASYMMETRIC_ENCRYPTION, + 'RSA_OAEP': AlgorithmCategory.ASYMMETRIC_ENCRYPTION, + 'HKDF': AlgorithmCategory.KEY_DERIVATION, + 'TLS12_PRF': AlgorithmCategory.KEY_DERIVATION, + 'TLS12_PSK_TO_MS': AlgorithmCategory.KEY_DERIVATION, + 'PBKDF': AlgorithmCategory.KEY_DERIVATION, + 'ECDH': AlgorithmCategory.KEY_AGREEMENT, + 'FFDH': AlgorithmCategory.KEY_AGREEMENT, + # KEY_AGREEMENT(...) is a key derivation with a key agreement component + 'KEY_AGREEMENT': AlgorithmCategory.KEY_DERIVATION, + 'JPAKE': AlgorithmCategory.PAKE, + } + for x in BLOCK_MAC_MODES: + CATEGORY_FROM_HEAD[x] = AlgorithmCategory.MAC + for x in BLOCK_CIPHER_MODES: + CATEGORY_FROM_HEAD[x] = AlgorithmCategory.CIPHER + for x in BLOCK_AEAD_MODES: + CATEGORY_FROM_HEAD[x] = AlgorithmCategory.AEAD + + def determine_category(self, expr: str, head: str) -> AlgorithmCategory: + """Return the category of the given algorithm expression. + + This function does not attempt to detect invalid inputs. + """ + prefix = head + while prefix: + if prefix in self.CATEGORY_FROM_HEAD: + return self.CATEGORY_FROM_HEAD[prefix] + if re.match(r'.*[0-9]\Z', prefix): + prefix = re.sub(r'_*[0-9]+\Z', r'', prefix) + else: + prefix = re.sub(r'_*[^_]*\Z', r'', prefix) + raise AlgorithmNotRecognized(expr) + + @staticmethod + def determine_wildcard(expr) -> bool: + """Whether the given algorithm expression is a wildcard. + + This function does not attempt to detect invalid inputs. + """ + if re.search(r'\bPSA_ALG_ANY_HASH\b', expr): + return True + if re.search(r'_AT_LEAST_', expr): + return True + return False + + def __init__(self, expr: str) -> None: + """Analyze an algorithm value. + + The algorithm must be expressed as a C expression containing only + calls to PSA algorithm constructor macros and numeric literals. + + This class is only programmed to handle valid expressions. Invalid + expressions may result in exceptions or in nonsensical results. + """ + self.expression = re.sub(r'\s+', r'', expr) + self.base_expression = self.determine_base(self.expression) + self.head = self.determine_head(self.base_expression) + self.category = self.determine_category(self.base_expression, self.head) + self.is_wildcard = self.determine_wildcard(self.expression)