Add new test vector "Silent payment to recipient with SP change (label=0)"

Fix compute output script ‘k’ bug - now increments for each output sharing the same scan key

Author: macgyver13

bip-0375/test_vectors.json

@@ -662,7 +662,7 @@
       "comment": "Two signers each contribute ECDH shares for their respective inputs"
     },
     {
-      "description": "Silent payment with change detection",
+      "description": "P2WPKH to silent payment with change detection",
       "psbt": "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",
       "input_keys": [
         {
@@ -713,6 +713,70 @@
       ],
       "comment": "Uses PSBT_OUT_SP_V0_LABEL and BIP32 derivation for change identification"
     },
+    {
+      "description": "Silent payment to recipient with SP change (label=0)",
+      "psbt": "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",
+      "input_keys": [
+        {
+          "input_index": 0,
+          "private_key": "e75f1990643539150761b0dc9eceb2ec0cf8636883eea2112d991dec3567a7b9",
+          "public_key": "03d357f7c0718f2478e3fd8f8ccc2729ddd8c0ccaeb1f02b181a6f44d43b9f8d8d",
+          "prevout_txid": "3ea4164ed0f3244e8e79dd4192ed4745a463ad3abcb28dd5e98202868a09d8c2",
+          "prevout_index": 0,
+          "prevout_scriptpubkey": "0014f8daf76ad803b0efa95d6cff8aee0891d3af1c8c",
+          "amount": 100000,
+          "witness_utxo": "a086010000000000160014f8daf76ad803b0efa95d6cff8aee0891d3af1c8c",
+          "sequence": 4294967295
+        }
+      ],
+      "scan_keys": [
+        {
+          "scan_pubkey": "02d029ff96de2cbcf782be4359c48620ea92bcdd6bef032b95158b91a1693fb4f8",
+          "spend_pubkey": "035434fa7d9abae85f18afee26e16fbb7888c88c56e3f93f5eee4dc0ef948fa5c4",
+          "label": 0
+        },
+        {
+          "scan_pubkey": "02d0e7de19c85516c83e19389595fcc4aaa2808c9d5dbb482573b589db0d4d43fb",
+          "spend_pubkey": "0365aac23ea95df8c8f473bb5abba7d58e28d3b46a34191bd4095c6dd5e6ad7341",
+          "label": null
+        }
+      ],
+      "expected_ecdh_shares": [
+        {
+          "scan_key": "02d0e7de19c85516c83e19389595fcc4aaa2808c9d5dbb482573b589db0d4d43fb",
+          "ecdh_result": "034807f86c259ace1ea7d269530bb97d7b61cc72d45bbc00f65630199d770b6f69",
+          "dleq_proof": "9600990a62cfd3db37b6f6e39c8d0bdafcb52a2dc3b6ecd28f31b854ae5e293f41956efd620fc1e015e79dbaf4e49d9d9eee3f08631b7b784dbfc176f264b8c2",
+          "is_global": false,
+          "input_index": 0
+        },
+        {
+          "scan_key": "02d029ff96de2cbcf782be4359c48620ea92bcdd6bef032b95158b91a1693fb4f8",
+          "ecdh_result": "0255164e7926d50d52a09ff990647a5e95c1db1bfc68a616fbc2da213927f98bff",
+          "dleq_proof": "c1d67f387882bf817915ea15821d64d5b3835c1fc05c558ce3d82492a17d908c10487dbb9bddc1080c8c2d9c1971b266083c69054e22193f244128ac66737e60",
+          "is_global": false,
+          "input_index": 0
+        }
+      ],
+      "expected_outputs": [
+        {
+          "output_index": 0,
+          "amount": 40000,
+          "script": "51206791e564c037c4f8200822d4e4451be9286a03ca7f558a9ec92d5ecf19fc7a41",
+          "is_silent_payment": true,
+          "sp_info": "02d0e7de19c85516c83e19389595fcc4aaa2808c9d5dbb482573b589db0d4d43fb0365aac23ea95df8c8f473bb5abba7d58e28d3b46a34191bd4095c6dd5e6ad7341",
+          "sp_label": null
+        },
+        {
+          "output_index": 1,
+          "amount": 55000,
+          "script": "5120a7ae5667bc9b772b30a022dd246e5890cc2d3b8012c406ee23485839aeab6a81",
+          "is_silent_payment": true,
+          "sp_info": "02d029ff96de2cbcf782be4359c48620ea92bcdd6bef032b95158b91a1693fb4f8035434fa7d9abae85f18afee26e16fbb7888c88c56e3f93f5eee4dc0ef948fa5c4",
+          "sp_label": 0
+        }
+      ],
+      "comment": "Demonstrates BIP-352 label=0 convention for Silent Payment change. Recipient output (output 0) has no label field. Change output (output 1) uses label=0 with PSBT_OUT_SP_V0_LABEL set. Both outputs are Silent Payments with different scan keys."
+    },
     {
       "description": "Multiple silent payment outputs to same scan key",
       "psbt": "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",

bip-0375/validator.py

@@ -180,6 +180,9 @@ def validate_bip352_outputs(
                 output_index = struct.unpack("<I", output_index_bytes)[0]
                 outpoints.append((txid, output_index))
 
+    # Track k values per scan key (k increments for each output per scan key)
+    scan_key_k_values = {}
+
     # Validate each silent payment output
     for output_idx, output_fields in enumerate(output_maps):
         # Only validate outputs with SP_V0_INFO (silent payment outputs)
@@ -193,6 +196,9 @@ def validate_bip352_outputs(
         scan_pubkey_bytes = sp_info[:33]
         spend_pubkey_bytes = sp_info[33:]
 
+        # Get k value for this scan key (starts at 0, increments for each output)
+        k = scan_key_k_values.get(scan_pubkey_bytes, 0)
+
         # Find matching ECDH share for this scan key
         ecdh_share_bytes = None
         summed_pubkey_bytes = None
@@ -256,7 +262,7 @@ def validate_bip352_outputs(
                 summed_pubkey_bytes=summed_pubkey_bytes,
                 ecdh_share_bytes=ecdh_share_bytes,
                 spend_pubkey_bytes=spend_pubkey_bytes,
-                k=output_idx,  # Use output index for k parameter
+                k=k,
             )
 
             # Compare with actual PSBT output script
@@ -268,6 +274,9 @@ def validate_bip352_outputs(
                         f"Output {output_idx} script doesn't match BIP-352 derivation",
                     )
 
+            # Increment k for this scan key after successful validation
+            scan_key_k_values[scan_pubkey_bytes] = k + 1
+
     return True, "BIP-352 output validation passed"