python: fix sign_verify_vector.json bug

It misclassifed a "verify error" vector as "verify fail" vector.
context: bitcoin/bips#2070 (comment)

Author: siv2r

README.md

@@ -1,13 +1,13 @@
 ```
-BIP: 445
-Title: FROST Signing Protocol for BIP340 Signatures
-Authors: Sivaram Dhakshinamoorthy <siv2ram@gmail.com>
-Status: Draft
-Type: Specification
-Assigned: 2026-01-30
-License: CC0-1.0
-Discussion: 2024-07-31: https://groups.google.com/g/bitcoindev/c/PeMp2HQl-H4/m/AcJtK0aKAwAJ
-Requires: 340
+  BIP: 445
+  Title: FROST Signing Protocol for BIP340 Signatures
+  Authors: Sivaram Dhakshinamoorthy <siv2ram@gmail.com>
+  Status: Draft
+  Type: Specification
+  Assigned: 2026-01-30
+  License: CC0-1.0
+  Discussion: 2024-07-31: https://groups.google.com/g/bitcoindev/c/PeMp2HQl-H4/m/AcJtK0aKAwAJ
+  Requires: 340
 ```
 
 ## Abstract
@@ -534,6 +534,7 @@ Algorithm *PartialSigVerify(psig, pubnonce<sub>1..u</sub>, signers_ctx, tweak<su
   - The list of tweak modes *is_xonly_t<sub>1..v</sub>* : *v* booleans
   - The message *m*: a byte array[^max-msg-len]
   - The index *i* of the signer in the list of public nonces where *0 < i ≤ u*
+- ValidateSignersCtx(signers_ctx); fail if that fails
 - Let *(_, _, u, id<sub>1..u</sub>, pubshare<sub>1..u</sub>, _) = signers_ctx*
 - Let *aggnonce = NonceAgg(pubnonce<sub>1..u</sub>, id<sub>1..u</sub>)*; fail if that fails
 - Let *session_ctx = (signers_ctx, aggnonce, v, tweak<sub>1..v</sub>, is_xonly_t<sub>1..v</sub>, m)*

python/gen_vectors.py

@@ -736,18 +736,6 @@ def generate_sign_verify_vectors():
         }
     )
     # --- Verify Fail Test Cases 3 ---
-    vectors["verify_fail_test_cases"].append(
-        {
-            "psig": bytes_to_hex(psig),
-            "id_indices": id_indices,
-            "pubshare_indices": [2] + pubshare_indices[1:],
-            "pubnonce_indices": pubnonce_indices,
-            "msg_index": msg_idx,
-            "signer_index": signer_idx,
-            "comment": "The signer's pubshare is not in the list of pubshares",
-        }
-    )
-    # --- Verify Fail Test Cases 4 ---
     vectors["verify_fail_test_cases"].append(
         {
             "psig": "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141",
@@ -790,6 +778,15 @@ def generate_sign_verify_vectors():
             "error": "value",
             "comment": "public nonces count is greater than ids and pubshares",
         },
+        {
+            "ids": [0, 1],
+            "pubshares": [2, 1],
+            "pubnonces": [0, 1],
+            "msg": 0,
+            "signer": 0,
+            "error": "value",
+            "comment": "The signer's pubshare is not in the list of pubshares",
+        },
     ]
     for case in verify_error_cases:
         curr_ids = [ids[i] for i in case["ids"]]

python/tests.py

@@ -233,12 +233,14 @@ def test_sign_verify_vectors():
         signer_index = test_case["signer_index"]
 
         signers_tmp = SignersContext(n, t, ids_tmp, pubshares_tmp, thresh_pk)
-        assert not partial_sig_verify_internal(
+        assert not partial_sig_verify(
             psig,
-            ids_tmp[signer_index],
-            pubnonces_tmp[signer_index],
-            pubshares_tmp[signer_index],
-            session_ctx,
+            pubnonces_tmp,
+            signers_tmp,
+            [],
+            [],
+            msg,
+            signer_index,
         )
 
     for test_case in verify_error_test_cases:

python/vectors/sign_verify_vectors.json

@@ -398,24 +398,6 @@
             "signer_index": 1,
             "comment": "Wrong signer index"
         },
-        {
-            "psig": "79DEFC679CF419BA7C48AF8F9526B5D510AAA4115B04DECDDE10CE9E06105334",
-            "id_indices": [
-                0,
-                1
-            ],
-            "pubshare_indices": [
-                2,
-                1
-            ],
-            "pubnonce_indices": [
-                0,
-                1
-            ],
-            "msg_index": 0,
-            "signer_index": 0,
-            "comment": "The signer's pubshare is not in the list of pubshares"
-        },
         {
             "psig": "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141",
             "id_indices": [
@@ -504,6 +486,28 @@
                 "message": "The pubnonces and ids arrays must have the same length."
             },
             "comment": "public nonces count is greater than ids and pubshares"
+        },
+        {
+            "psig": "79DEFC679CF419BA7C48AF8F9526B5D510AAA4115B04DECDDE10CE9E06105334",
+            "id_indices": [
+                0,
+                1
+            ],
+            "pubshare_indices": [
+                2,
+                1
+            ],
+            "pubnonce_indices": [
+                0,
+                1
+            ],
+            "msg_index": 0,
+            "signer_index": 0,
+            "error": {
+                "type": "ValueError",
+                "message": "The provided key material is incorrect."
+            },
+            "comment": "The signer's pubshare is not in the list of pubshares"
         }
     ]
 }