Storage format tests: exercise operations with keys

In key read tests, add usage flags that are suitable for the key type and
algorithm. This way, the call to exercise_key() in the test not only checks
that exporting the key is possible, but also that operations on the key are
possible.

This triggers a number of failures in edge cases where the generator
generates combinations that are not valid, which will be fixed in subsequent
commits.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

scripts/mbedtls_dev/crypto_knowledge.py

@@ -20,7 +20,7 @@ This module is entirely based on the PSA API.
 
 import enum
 import re
-from typing import Iterable, Optional, Tuple
+from typing import Iterable, List, Optional, Tuple
 
 from mbedtls_dev.asymmetric_key_data import ASYMMETRIC_KEY_DATA
 
@@ -422,3 +422,31 @@ class Algorithm:
            self.is_key_agreement_with_derivation():
             return True
         return False
+
+    def usage_flags(self, public: bool = False) -> List[str]:
+        """The list of usage flags describing operations that can perform this algorithm.
+
+        If public is true, only return public-key operations, not private-key operations.
+        """
+        if self.category == AlgorithmCategory.HASH:
+            flags = []
+        elif self.category == AlgorithmCategory.MAC:
+            flags = ['SIGN_HASH', 'SIGN_MESSAGE',
+                     'VERIFY_HASH', 'VERIFY_MESSAGE']
+        elif self.category == AlgorithmCategory.CIPHER or \
+             self.category == AlgorithmCategory.AEAD:
+            flags = ['DECRYPT', 'ENCRYPT']
+        elif self.category == AlgorithmCategory.SIGN:
+            flags = ['VERIFY_HASH', 'VERIFY_MESSAGE']
+            if not public:
+                flags += ['SIGN_HASH', 'SIGN_MESSAGE']
+        elif self.category == AlgorithmCategory.ASYMMETRIC_ENCRYPTION:
+            flags = ['ENCRYPT']
+            if not public:
+                flags += ['DECRYPT']
+        elif self.category == AlgorithmCategory.KEY_DERIVATION or \
+             self.category == AlgorithmCategory.KEY_AGREEMENT:
+            flags = ['DERIVE']
+        else:
+            raise AlgorithmNotRecognized(self.expression)
+        return ['PSA_KEY_USAGE_' + flag for flag in flags]

tests/scripts/generate_psa_tests.py

@@ -645,8 +645,11 @@ class StorageFormat:
         If alg is not None, this key allows it.
         """
         usage_flags = ['PSA_KEY_USAGE_EXPORT']
-        alg1 = 0 if alg is None else alg.expression #type: psa_storage.Exprable
+        alg1 = 0 #type: psa_storage.Exprable
         alg2 = 0
+        if alg is not None:
+            alg1 = alg.expression
+            usage_flags += alg.usage_flags(public=kt.is_public())
         key_material = kt.key_material(bits)
         description = 'type: {} {}-bit'.format(kt.short_expression(1), bits)
         if alg is not None: