From d31236854b186d730b3e8e0a669019b88e32c956 Mon Sep 17 00:00:00 2001
From: macgyver13 <4712150+macgyver13@users.noreply.github.com>
Date: Tue, 2 Jun 2026 11:58:40 -0400
Subject: [PATCH] BIP-375: update validation to match sorting outputs with same
 scan key

Fix output script validation for silent payment output ordering when multiple
outputs share the same scan key (labeled addresses of one recipient).
---
 bip-0375/validator/validate_psbt.py | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/bip-0375/validator/validate_psbt.py b/bip-0375/validator/validate_psbt.py
index 054f4fd6..b232ec97 100644
--- a/bip-0375/validator/validate_psbt.py
+++ b/bip-0375/validator/validate_psbt.py
@@ -233,7 +233,7 @@ def validate_dleq_proof(
 ) -> Tuple[bool, str]:
     """
     Verify a DLEQ proof for silent payments
-    
+
     Checks:
     - ECDH share and DLEQ proof lengths
     - Verify DLEQ proof correctness
@@ -323,15 +323,18 @@ def validate_output_scripts(psbt: PSBT) -> Tuple[bool, str]:
             output_index = struct.unpack("<I", output_index_bytes)[0]
             outpoints.append(COutPoint(txid_int, output_index))
 
+    # Silent payment codes sorted lexicographically, ties broken by output index
+    sp_outputs = [
+        (output_map[PSBT_OUT_SP_V0_INFO], output_idx, output_map)
+        for output_idx, output_map in enumerate(psbt.o)
+        if PSBT_OUT_SP_V0_INFO in output_map
+    ]
+    sp_outputs.sort(key=lambda entry: (entry[0], entry[1]))
+
     # Track k values per scan key
     scan_key_k_values = {}
 
-    # Validate each SP output
-    for output_idx, output_map in enumerate(psbt.o):
-        if PSBT_OUT_SP_V0_INFO not in output_map:
-            continue  # Skip non-SP outputs
-
-        sp_info = output_map[PSBT_OUT_SP_V0_INFO]
+    for sp_info, output_idx, output_map in sp_outputs:
         scan_pubkey_bytes = sp_info[:33]
         spend_pubkey_bytes = sp_info[33:]