New algorithm PSA_ALG_RSA_PSS_ANY_SALT

This is a variant of PSA_ALG_RSA_PSS which currently has exactly the same
behavior, but is intended to have a different behavior when verifying
signatures.

In a subsequent commit, PSA_ALG_RSA_PSS will change to requiring the salt
length to be what it would produce when signing, as is currently documented,
whereas PSA_ALG_RSA_PSS_ANY_SALT will retain the current behavior of
allowing any salt length (including 0).

Changes in this commit:

* New algorithm constructor PSA_ALG_RSA_PSS_ANY_SALT.
* New predicates PSA_ALG_IS_RSA_PSS_STANDARD_SALT (corresponding to
  PSA_ALG_RSA_PSS) and PSA_ALG_IS_RSA_PSS_ANY_SALT (corresponding to
  PSA_ALG_RSA_PSS_ANY_SALT).
* Support for the new predicates in macro_collector.py (needed for
  generate_psa_constant_names).

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

include/psa/crypto_values.h

@@ -886,7 +886,7 @@
  * algorithm parametrized with any supported hash.
  *
  * That is, suppose that `PSA_xxx_SIGNATURE` is one of the following macros:
- * - #PSA_ALG_RSA_PKCS1V15_SIGN, #PSA_ALG_RSA_PSS,
+ * - #PSA_ALG_RSA_PKCS1V15_SIGN, #PSA_ALG_RSA_PSS, #PSA_ALG_RSA_PSS_ANY_SALT,
  * - #PSA_ALG_ECDSA, #PSA_ALG_DETERMINISTIC_ECDSA.
  * Then you may create and use a key as follows:
  * - Set the key usage field using #PSA_ALG_ANY_HASH, for example:
@@ -1341,6 +1341,7 @@
     (((alg) & ~PSA_ALG_HASH_MASK) == PSA_ALG_RSA_PKCS1V15_SIGN_BASE)
 
 #define PSA_ALG_RSA_PSS_BASE               ((psa_algorithm_t)0x06000300)
+#define PSA_ALG_RSA_PSS_ANY_SALT_BASE      ((psa_algorithm_t)0x06001300)
 /** RSA PSS signature with hashing.
  *
  * This is the signature scheme defined by RFC 8017
@@ -1361,9 +1362,72 @@
  */
 #define PSA_ALG_RSA_PSS(hash_alg)                               \
     (PSA_ALG_RSA_PSS_BASE | ((hash_alg) & PSA_ALG_HASH_MASK))
-#define PSA_ALG_IS_RSA_PSS(alg)                                 \
+
+/** RSA PSS signature with hashing with relaxed verification.
+ *
+ * This algorithm has the same behavior as #PSA_ALG_RSA_PSS when signing,
+ * but allows an arbitrary salt length (including \c 0) when verifying a
+ * signature.
+ *
+ * \param hash_alg      A hash algorithm (\c PSA_ALG_XXX value such that
+ *                      #PSA_ALG_IS_HASH(\p hash_alg) is true).
+ *                      This includes #PSA_ALG_ANY_HASH
+ *                      when specifying the algorithm in a usage policy.
+ *
+ * \return              The corresponding RSA PSS signature algorithm.
+ * \return              Unspecified if \p hash_alg is not a supported
+ *                      hash algorithm.
+ */
+#define PSA_ALG_RSA_PSS_ANY_SALT(hash_alg)                      \
+    (PSA_ALG_RSA_PSS_ANY_SALT_BASE | ((hash_alg) & PSA_ALG_HASH_MASK))
+
+/** Whether the specified algorithm is RSA PSS with standard salt.
+ *
+ * \param alg           An algorithm value or an algorithm policy wildcard.
+ *
+ * \return              1 if \p alg is of the form
+ *                      #PSA_ALG_RSA_PSS(\c hash_alg),
+ *                      where \c hash_alg is a hash algorithm or
+ *                      #PSA_ALG_ANY_HASH. 0 otherwise.
+ *                      This macro may return either 0 or 1 if \p alg is not
+ *                      a supported algorithm identifier or policy.
+ */
+#define PSA_ALG_IS_RSA_PSS_STANDARD_SALT(alg)                   \
     (((alg) & ~PSA_ALG_HASH_MASK) == PSA_ALG_RSA_PSS_BASE)
 
+/** Whether the specified algorithm is RSA PSS with any salt.
+ *
+ * \param alg           An algorithm value or an algorithm policy wildcard.
+ *
+ * \return              1 if \p alg is of the form
+ *                      #PSA_ALG_RSA_PSS_ANY_SALT_BASE(\c hash_alg),
+ *                      where \c hash_alg is a hash algorithm or
+ *                      #PSA_ALG_ANY_HASH. 0 otherwise.
+ *                      This macro may return either 0 or 1 if \p alg is not
+ *                      a supported algorithm identifier or policy.
+ */
+#define PSA_ALG_IS_RSA_PSS_ANY_SALT(alg)                                \
+    (((alg) & ~PSA_ALG_HASH_MASK) == PSA_ALG_RSA_PSS_ANY_SALT_BASE)
+
+/** Whether the specified algorithm is RSA PSS.
+ *
+ * This includes any of the RSA PSS algorithm variants, regardless of the
+ * constraints on salt length.
+ *
+ * \param alg           An algorithm value or an algorithm policy wildcard.
+ *
+ * \return              1 if \p alg is of the form
+ *                      #PSA_ALG_RSA_PSS(\c hash_alg) or
+ *                      #PSA_ALG_RSA_PSS_ANY_SALT_BASE(\c hash_alg),
+ *                      where \c hash_alg is a hash algorithm or
+ *                      #PSA_ALG_ANY_HASH. 0 otherwise.
+ *                      This macro may return either 0 or 1 if \p alg is not
+ *                      a supported algorithm identifier or policy.
+ */
+#define PSA_ALG_IS_RSA_PSS(alg)                                 \
+    ((((alg) & ~PSA_ALG_HASH_MASK) == PSA_ALG_RSA_PSS_BASE) ||  \
+     (((alg) & ~PSA_ALG_HASH_MASK) == PSA_ALG_RSA_PSS_ANY_SALT_BASE))
+
 #define PSA_ALG_ECDSA_BASE                      ((psa_algorithm_t)0x06000600)
 /** ECDSA signature with hashing.
  *

scripts/mbedtls_dev/macro_collector.py

@@ -250,6 +250,8 @@ class PSAMacroCollector(PSAMacroEnumerator):
         suffix = name[len(prefix):]
         if suffix in ['DSA', 'ECDSA']:
             midfix += 'RANDOMIZED_'
+        elif suffix == 'RSA_PSS':
+            suffix += '_STANDARD_SALT'
         return prefix + midfix + suffix
 
     def record_algorithm_subtype(self, name: str, expansion: str) -> None:

tests/suites/test_suite_psa_crypto_metadata.data

@@ -182,6 +182,10 @@ Asymmetric signature: RSA PSS SHA-256
 depends_on:PSA_WANT_ALG_RSA_PSS:PSA_WANT_ALG_SHA_256
 asymmetric_signature_algorithm:PSA_ALG_RSA_PSS( PSA_ALG_SHA_256 ):ALG_IS_RSA_PSS | ALG_IS_HASH_AND_SIGN
 
+Asymmetric signature: RSA PSS-any-salt SHA-256
+depends_on:PSA_WANT_ALG_RSA_PSS:PSA_WANT_ALG_SHA_256
+asymmetric_signature_algorithm:PSA_ALG_RSA_PSS_ANY_SALT( PSA_ALG_SHA_256 ):ALG_IS_RSA_PSS | ALG_IS_HASH_AND_SIGN
+
 Asymmetric signature: randomized ECDSA (no hashing)
 depends_on:PSA_WANT_ALG_ECDSA
 asymmetric_signature_algorithm:PSA_ALG_ECDSA_ANY:ALG_IS_ECDSA | ALG_IS_RANDOMIZED_ECDSA | ALG_IS_HASH_AND_SIGN
@@ -214,6 +218,10 @@ Asymmetric signature: RSA PSS with wildcard hash
 depends_on:PSA_WANT_ALG_RSA_PSS
 asymmetric_signature_wildcard:PSA_ALG_RSA_PSS( PSA_ALG_ANY_HASH ):ALG_IS_RSA_PSS
 
+Asymmetric signature: RSA PSS-any-salt with wildcard hash
+depends_on:PSA_WANT_ALG_RSA_PSS
+asymmetric_signature_wildcard:PSA_ALG_RSA_PSS_ANY_SALT( PSA_ALG_ANY_HASH ):ALG_IS_RSA_PSS
+
 Asymmetric signature: randomized ECDSA with wildcard hash
 depends_on:PSA_WANT_ALG_ECDSA
 asymmetric_signature_wildcard:PSA_ALG_ECDSA( PSA_ALG_ANY_HASH ):ALG_IS_ECDSA | ALG_IS_RANDOMIZED_ECDSA