BIP352: align reference address decoding with silent payment rules

bip-0352/reference.py

@@ -14,7 +14,7 @@
 from secp256k1lab.util import tagged_hash, hash_sha256
 
 
-from bech32m import convertbits, bech32_encode, decode, Encoding
+from bech32m import bech32_decode, bech32_encode, convertbits, Encoding
 from bitcoin_utils import (
         deser_txid,
         from_hex,
@@ -116,11 +116,20 @@ def create_labeled_silent_payment_address(b_scan: Scalar, B_spend: GE, m: int, h
 
 
 def decode_silent_payment_address(address: str, hrp: str = "tsp") -> Tuple[GE, GE]:
-    _, data = decode(hrp, address)
-    if data is None:
+    hrpgot, data, spec = bech32_decode(address)
+    if hrpgot != hrp or spec != Encoding.BECH32M or data is None or not data:
         return GE(), GE()
-    B_scan = GE.from_bytes_compressed(data[:33])
-    B_spend = GE.from_bytes_compressed(data[33:])
+
+    version = data[0]
+    if version == 31:
+        return GE(), GE()
+
+    decoded = convertbits(data[1:], 5, 8, False)
+    if decoded is None or len(decoded) < 66 or (version == 0 and len(decoded) != 66):
+        return GE(), GE()
+
+    B_scan = GE.from_bytes_compressed(decoded[:33])
+    B_spend = GE.from_bytes_compressed(decoded[33:66])
 
     return B_scan, B_spend
 

bip-0352/test_address_decoding.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+
+import unittest
+
+from bech32m import Encoding, bech32_encode, convertbits
+from reference import decode_silent_payment_address
+from secp256k1lab.secp256k1 import GE
+
+
+SCAN_KEY = bytes.fromhex("0220bcfac5b99e04ad1a06ddfb016ee13582609d60b6291e98d01a9bc9a16c96d4")
+SPEND_KEY = bytes.fromhex("025cc9856d6f8375350e123978daac200c260cb5b5ae83106cab90484dcd8fcf36")
+PAYLOAD = SCAN_KEY + SPEND_KEY
+
+
+def make_address(version, payload=PAYLOAD, spec=Encoding.BECH32M):
+    data = convertbits(payload, 8, 5)
+    return bech32_encode("tsp", [version] + data, spec)
+
+
+class SilentPaymentAddressDecodingTest(unittest.TestCase):
+    def test_accepts_higher_forward_compatible_version(self):
+        scan, spend = decode_silent_payment_address(make_address(17))
+        self.assertEqual(scan, GE.from_bytes_compressed(SCAN_KEY))
+        self.assertEqual(spend, GE.from_bytes_compressed(SPEND_KEY))
+
+    def test_discards_forward_compatible_extension_data(self):
+        scan, spend = decode_silent_payment_address(make_address(1, PAYLOAD + b"extension"))
+        self.assertEqual(scan, GE.from_bytes_compressed(SCAN_KEY))
+        self.assertEqual(spend, GE.from_bytes_compressed(SPEND_KEY))
+
+    def test_rejects_bech32_for_version_zero(self):
+        scan, spend = decode_silent_payment_address(make_address(0, spec=Encoding.BECH32))
+        self.assertTrue(scan.infinity)
+        self.assertTrue(spend.infinity)
+
+    def test_rejects_extra_data_for_version_zero(self):
+        scan, spend = decode_silent_payment_address(make_address(0, PAYLOAD + b"extension"))
+        self.assertTrue(scan.infinity)
+        self.assertTrue(spend.infinity)
+
+    def test_rejects_version_31(self):
+        scan, spend = decode_silent_payment_address(make_address(31))
+        self.assertTrue(scan.infinity)
+        self.assertTrue(spend.infinity)
+
+
+if __name__ == "__main__":
+    unittest.main()