Always configure PSA-based keys for encryption and decryption
Mbed TLS cipher layer allows usage of keys for other purposes
than indicated in the `operation` parameter of `mbedtls_cipher_setkey()`.
The semantics of the PSA Crypto API, in contrast, checks key
usage against the key policy.
As a remedy, this commit modifies the PSA key slot setup to
always allow both encryption and decryption.
diff --git a/library/cipher.c b/library/cipher.c
index a83d3c6..243c739 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -310,7 +310,13 @@
/* Setup policy for the new key slot. */
psa_key_policy_init( &key_policy );
- key_usage = mbedtls_psa_translate_cipher_operation( operation );
+
+ /* Mbed TLS' cipher layer doesn't enforce the mode of operation
+ * (encrypt vs. decrypt): it is possible to setup a key for encryption
+ * and use it for AEAD decryption. Until tests relying on this
+ * are changed, allow any usage in PSA. */
+ /* key_usage = mbedtls_psa_translate_cipher_operation( operation ); */
+ key_usage = PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_DECRYPT;
psa_key_policy_set_usage( &key_policy, key_usage, cipher_psa->alg );
status = psa_set_key_policy( cipher_psa->slot, &key_policy );
if( status != PSA_SUCCESS )