commit e0e9c7c417e694b30870a9068769f1ca933f7d42
author Gilles Peskine <Gilles.Peskine@arm.com> Wed Oct 17 18:28:05 2018 +0200
committer Gilles Peskine <Gilles.Peskine@arm.com> Wed Oct 17 18:30:47 2018 +0200
tree 0fd67d9aed33aab7969754390291754b15c47416
parent 57fbdb19397ec8b45a002252f5f187d7f6c76a19

New macro PSA_ALG_FULL_LENGTH_MAC

Provide a documented way of constructing the full-length MAC algorithm
from a truncated version.

include/psa/crypto.h

diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index 48c9713..99c4b52 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -803,6 +803,21 @@
     (((alg) & ~PSA_ALG_MAC_TRUNCATION_MASK) |                           \
      ((mac_length) << PSA_MAC_TRUNCATION_OFFSET & PSA_ALG_MAC_TRUNCATION_MASK))
 
+/** Macro to build the base MAC algorithm corresponding to a truncated
+ * MAC algorithm.
+ *
+ * \param alg           A MAC algorithm identifier (value of type
+ *                      #psa_algorithm_t such that #PSA_ALG_IS_MAC(\p alg)
+ *                      is true). This may be a truncated or untruncated
+ *                      MAC algorithm.
+ *
+ * \return              The corresponding base MAC algorithm.
+ * \return              Unspecified if \p alg is not a supported
+ *                      MAC algorithm.
+ */
+#define PSA_ALG_FULL_LENGTH_MAC(alg)            \
+    ((alg) & ~PSA_ALG_MAC_TRUNCATION_MASK)
+
 /** Length to which a MAC algorithm is truncated.
  *
  * \param alg           A MAC algorithm identifier (value of type

library/psa_crypto.c

diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index ab9ec72..6b01c13 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1527,7 +1527,7 @@
     psa_key_usage_t usage =
         is_sign ? PSA_KEY_USAGE_SIGN : PSA_KEY_USAGE_VERIFY;
     unsigned char truncated = PSA_MAC_TRUNCATED_LENGTH( alg );
-    psa_algorithm_t full_length_alg = alg & ~PSA_ALG_MAC_TRUNCATION_MASK;
+    psa_algorithm_t full_length_alg = PSA_ALG_FULL_LENGTH_MAC( alg );
 
     status = psa_mac_init( operation, full_length_alg );
     if( status != PSA_SUCCESS )

tests/suites/test_suite_psa_crypto_metadata.function

diff --git a/tests/suites/test_suite_psa_crypto_metadata.function b/tests/suites/test_suite_psa_crypto_metadata.function
index 9cb68b9..215110a 100644
--- a/tests/suites/test_suite_psa_crypto_metadata.function
+++ b/tests/suites/test_suite_psa_crypto_metadata.function
@@ -198,6 +198,7 @@
 
     mac_algorithm_core( alg, classification_flags,
                         key_type, key_bits, length );
+    TEST_ASSERT( PSA_ALG_FULL_LENGTH_MAC( alg ) == alg );
     TEST_ASSERT( length <= PSA_MAC_MAX_SIZE );
 
     /* Truncated versions */
@@ -206,6 +207,7 @@
         psa_algorithm_t truncated_alg = PSA_ALG_TRUNCATED_MAC( alg, n );
         mac_algorithm_core( truncated_alg, classification_flags,
                             key_type, key_bits, n );
+        TEST_ASSERT( PSA_ALG_FULL_LENGTH_MAC( truncated_alg ) == alg );
         /* Check that calling PSA_ALG_TRUNCATED_MAC twice gives the length
          * of the outer truncation (even if the outer length is smaller than
          * the inner length). */