Wycheproof: Check K value and reject unrecognized vector fields

Previous versions of the `semi_expanded_keys` Wycheproof test type
did not include a `K` output. Accordingly, the Wycheproof client
would only check if the test driver produced `K` upon a successful
run, but not compare it to anything from the Wycheproof test data.

A recent commit 782238d4 added the expected `K` to the `semi_expanded_keys`
test schema. This commit modifies the Wycheproof client for this test
to check the calculated `K` against this expected `K`.

The above commit also added `ek`, but this is merely the PK embedded in the
SK, and not returned from mlkem-native's API. We therefore ignore the value.

To avoid a similar extension of the test schema go unnoticed in the future,
we explicitly list the keys of each schema that we know about and handle,
and error when new field are added.

Signed-off-by: Hanno Becker <beckphan@amazon.co.uk>

Author: hanno-becker

test/wycheproof/wycheproof_client.py

@@ -45,6 +45,25 @@
     "ML-KEM-1024": 1024,
 }
 
+# Fields each test-case handler knows how to interpret. If Wycheproof adds a
+# new field to a schema, an unrecognized key here means it may carry
+# information we are silently failing to check; fail loudly instead.
+KNOWN_FIELDS = {
+    "keygen_seed": {"tcId", "comment", "result", "seed", "ek", "dk"},
+    "encaps": {"tcId", "comment", "flags", "result", "ek", "m", "c", "K"},
+    "semi_expanded_decaps": {
+        "tcId",
+        "comment",
+        "flags",
+        "result",
+        "dk",
+        "c",
+        "ek",
+        "K",
+    },
+    "combined": {"tcId", "comment", "flags", "result", "seed", "ek", "c", "K"},
+}
+
 
 def err(msg, **kwargs):
     print(msg, file=sys.stderr, **kwargs)
@@ -79,6 +98,14 @@ def download_wycheproof_files(data_dir):
     return True
 
 
+def check_known_fields(kind, tc):
+    unknown = set(tc.keys()) - KNOWN_FIELDS[kind]
+    assert not unknown, (
+        f"Unrecognized field(s) {sorted(unknown)} in {kind} tcId={tc['tcId']}; "
+        "Wycheproof schema may have grown a new field this client doesn't check"
+    )
+
+
 def get_binary(level):
     basedir = f"./test/build/mlkem{level}/bin"
     return f"{basedir}/wycheproof_mlkem{level}"
@@ -108,6 +135,7 @@ def run_keygen_seed_test(data_file):
         level = PARAMETER_SET_TO_LEVEL[tg["parameterSet"]]
         binary = get_binary(level)
         for tc in tg["tests"]:
+            check_known_fields("keygen_seed", tc)
             info(f"  tcId={tc['tcId']} ... ", end="")
             out = run_binary([binary, "keygen_seed", f"seed={tc['seed']}"])
             if tc["result"] == "valid":
@@ -137,6 +165,7 @@ def run_encaps_test(data_file):
         level = PARAMETER_SET_TO_LEVEL[tg["parameterSet"]]
         binary = get_binary(level)
         for tc in tg["tests"]:
+            check_known_fields("encaps", tc)
             info(f"  tcId={tc['tcId']} ... ", end="")
             out = run_binary([binary, "encaps", f"ek={tc['ek']}", f"m={tc['m']}"])
             if tc["result"] == "invalid":
@@ -171,6 +200,7 @@ def run_semi_expanded_decaps_test(data_file):
         level = PARAMETER_SET_TO_LEVEL[tg["parameterSet"]]
         binary = get_binary(level)
         for tc in tg["tests"]:
+            check_known_fields("semi_expanded_decaps", tc)
             info(f"  tcId={tc['tcId']} ... ", end="")
             out = run_binary([binary, "decaps", f"dk={tc['dk']}", f"c={tc['c']}"])
             if tc["result"] == "invalid":
@@ -179,7 +209,10 @@ def run_semi_expanded_decaps_test(data_file):
                     f"binary success on invalid tcId={tc['tcId']}"
                 )
             elif tc["result"] == "valid":
-                assert "K" in out, f"missing K in output tcId={tc['tcId']}"
+                assert "K" in tc, f"missing K in test vector tcId={tc['tcId']}"
+                assert out["K"].upper() == tc["K"].upper(), (
+                    f"K mismatch tcId={tc['tcId']}"
+                )
             else:
                 assert False, (
                     f"Unsupported test result '{tc['result']}' for tcId={tc['tcId']}"
@@ -200,6 +233,7 @@ def run_combined_test(data_file):
         level = PARAMETER_SET_TO_LEVEL[tg["parameterSet"]]
         binary = get_binary(level)
         for tc in tg["tests"]:
+            check_known_fields("combined", tc)
             info(f"  tcId={tc['tcId']} ... ", end="")
             # Generate keypair from seed
             keygen_out = run_binary([binary, "keygen_seed", f"seed={tc['seed']}"])