commit 81a08830bb4236ab5c1c502557a30abe9f9508b8
author Udi Jonnalagadda <udij@google.com> Thu Aug 12 13:58:21 2021 -0700
committer udinator <udij@google.com> Thu Aug 12 19:41:54 2021 -0700
tree c6623b9bbbfcc784c9fd7680e671d1c30c0a8dc4
parent 5d06aaca0cd7b5d06e8c1e8a17b37587943f5551

[dv/kmac] Fix constraints on invalid mode/strength

This PR fixes how the TB constrains invalid mode/strength combinations
for error cases, currently if such an error case is selected, the TB can
  still generate a valid combination - this is now changed such that the
  TB can only generate invalid combinations.

Signed-off-by: Udi Jonnalagadda <udij@google.com>

hw/ip/kmac/dv/env/seq_lib/kmac_base_vseq.sv

diff --git a/hw/ip/kmac/dv/env/seq_lib/kmac_base_vseq.sv b/hw/ip/kmac/dv/env/seq_lib/kmac_base_vseq.sv
index bf8f1b6..8af0988 100644
--- a/hw/ip/kmac/dv/env/seq_lib/kmac_base_vseq.sv
+++ b/hw/ip/kmac/dv/env/seq_lib/kmac_base_vseq.sv
@@ -140,16 +140,22 @@
     }
   }
 
+  // Constrain valid and invalid mode/strength combinations based on the following:
+  // - only 128/256 bit strengths are supported for Shake/CShake
+  // - 128 bit strength is not supported for Sha3
   constraint strength_c {
     solve kmac_err_type before hash_mode;
     solve kmac_err_type before strength;
 
-    if (kmac_err_type != kmac_pkg::ErrUnexpectedModeStrength) {
-      // only 128/256 bit strengths are supported for the XOFs
+    if (kmac_err_type == kmac_pkg::ErrUnexpectedModeStrength) {
+      (hash_mode inside {sha3_pkg::Shake, sha3_pkg::CShake}) ->
+        !(strength inside {sha3_pkg::L128, sha3_pkg::L256});
+
+      (hash_mode == sha3_pkg::Sha3) -> (strength == sha3_pkg::L128);
+    } else {
       (hash_mode inside {sha3_pkg::Shake, sha3_pkg::CShake}) ->
         (strength inside {sha3_pkg::L128, sha3_pkg::L256});
 
-      // SHA3-128 is not supported
       (hash_mode == sha3_pkg::Sha3) -> (strength != sha3_pkg::L128);
     }
   }