Merge bitcoin/bitcoin#28336: rpc: parse legacy pubkeys consistently with specific error messages

98570fe29bb08d7edc48011aa6b9731c6ab4ed2e test: add coverage for parsing cryptographically invalid pubkeys (Sebastian Falbesoner)
c740b154d193b91ca42f18759098d3fef6eaab05 rpc: use `HexToPubKey` helper for all legacy pubkey-parsing RPCs (Sebastian Falbesoner)
100e8a75bf5d8196c005331bd8f2ed42ada6d8d0 rpc: check and throw specific pubkey parsing errors in `HexToPubKey` (Sebastian Falbesoner)

Pull request description:

  Parsing legacy public keys can fail for three reasons (in this order):
  - pubkey is not in hex
  - pubkey has an invalid length (not 33 or 65 bytes for compressed/uncompressed, respectively)
  - pubkey is crytographically invalid, i.e. is not on curve (`CPubKey.IsFullyValid()` check)

  Many RPCs currently perform these checks manually with different error messages, even though we already have a `HexToPubKey` helper. This PR puts all three checks in this helper (the length check was done on the call-sites before), adds specific error messages for each case, and consequently uses it for all RPCs that parse legacy pubkeys. This leads to deduplicated code and also to more consistent and detailed error messages for the user.

  Affected RPC calls are `createmultisig`, `addmultisigaddress`, `importpubkey`, `importmulti`, `fundrawtransaction`, `walletcreatefundedpsbt`, `send` and `sendall`.

  Note that the error code (-5 a.k.a. `RPC_INVALID_ADDRESS_OR_KEY`) doesn't change in any of the causes, so the changes are not breaking RPC API compatibility. Only the messages are more specific.

  The last commits adds test coverage for the cryptographically invalid (not-on-curve) pubkey case which wasn't exercised before.

ACKs for top commit:
  stratospher:
    tested ACK 98570fe.
  davidgumberg:
    ACK https://github.com/bitcoin/bitcoin/pull/28336/commits/98570fe29bb08d7edc48011aa6b9731c6ab4ed2e
  Eunovo:
    Tested ACK https://github.com/bitcoin/bitcoin/pull/28336/commits/98570fe29bb08d7edc48011aa6b9731c6ab4ed2e
  achow101:
    ACK 98570fe29bb08d7edc48011aa6b9731c6ab4ed2e

Tree-SHA512: cfa474176e95b5b18f3a9da28fdd9e87195cd58994c1331198f2840925fff322fd323a6371feab74a1b32e4b9ea58a6dc732fa751b4cdd45402c1029af609ece

3 files changed, 10 insertions, 7 deletions

diff --git a/test/functional/rpc_rawtransaction.py b/test/functional/rpc_rawtransaction.py
index 12697e9d0c..3978c80dde 100755
--- a/test/functional/rpc_rawtransaction.py
+++ b/test/functional/rpc_rawtransaction.py
@@ -490,11 +490,11 @@ class RawTransactionsTest(BitcoinTestFramework):
         addr2Obj = self.nodes[2].getaddressinfo(addr2)
 
         # Tests for createmultisig and addmultisigaddress
-        assert_raises_rpc_error(-5, "Invalid public key", self.nodes[0].createmultisig, 1, ["01020304"])
+        assert_raises_rpc_error(-5, 'Pubkey "01020304" must have a length of either 33 or 65 bytes', self.nodes[0].createmultisig, 1, ["01020304"])
         # createmultisig can only take public keys
         self.nodes[0].createmultisig(2, [addr1Obj['pubkey'], addr2Obj['pubkey']])
         # addmultisigaddress can take both pubkeys and addresses so long as they are in the wallet, which is tested here
-        assert_raises_rpc_error(-5, "Invalid public key", self.nodes[0].createmultisig, 2, [addr1Obj['pubkey'], addr1])
+        assert_raises_rpc_error(-5, f'Pubkey "{addr1}" must be a hex string', self.nodes[0].createmultisig, 2, [addr1Obj['pubkey'], addr1])
 
         mSigObj = self.nodes[2].addmultisigaddress(2, [addr1Obj['pubkey'], addr1])['address']
 
diff --git a/test/functional/wallet_basic.py b/test/functional/wallet_basic.py
index 56228d2bad..1b2b8ec1f3 100755
--- a/test/functional/wallet_basic.py
+++ b/test/functional/wallet_basic.py
@@ -461,10 +461,13 @@ class WalletTest(BitcoinTestFramework):
             assert_raises_rpc_error(-5, "Invalid Bitcoin address or script", self.nodes[0].importaddress, "invalid")
 
             # This will raise an exception for attempting to import a pubkey that isn't in hex
-            assert_raises_rpc_error(-5, "Pubkey must be a hex string", self.nodes[0].importpubkey, "not hex")
+            assert_raises_rpc_error(-5, 'Pubkey "not hex" must be a hex string', self.nodes[0].importpubkey, "not hex")
 
-            # This will raise an exception for importing an invalid pubkey
-            assert_raises_rpc_error(-5, "Pubkey is not a valid public key", self.nodes[0].importpubkey, "5361746f736869204e616b616d6f746f")
+            # This will raise exceptions for importing a pubkeys with invalid length / invalid coordinates
+            too_short_pubkey = "5361746f736869204e616b616d6f746f"
+            assert_raises_rpc_error(-5, f'Pubkey "{too_short_pubkey}" must have a length of either 33 or 65 bytes', self.nodes[0].importpubkey, too_short_pubkey)
+            not_on_curve_pubkey = bytes([4] + [0]*64).hex()  # pubkey with coordinates (0,0) is not on curve
+            assert_raises_rpc_error(-5, f'Pubkey "{not_on_curve_pubkey}" must be cryptographically valid', self.nodes[0].importpubkey, not_on_curve_pubkey)
 
             # Bech32m addresses cannot be imported into a legacy wallet
             assert_raises_rpc_error(-5, "Bech32m addresses cannot be imported into legacy wallets", self.nodes[0].importaddress, "bcrt1p0xlxvlhemja6c4dqv22uapctqupfhlxm9h8z3k2e72q4k9hcz7vqc8gma6")
diff --git a/test/functional/wallet_fundrawtransaction.py b/test/functional/wallet_fundrawtransaction.py
index ff4648e638..71c883f166 100755
--- a/test/functional/wallet_fundrawtransaction.py
+++ b/test/functional/wallet_fundrawtransaction.py
@@ -1054,8 +1054,8 @@ class RawTransactionsTest(BitcoinTestFramework):
         assert_raises_rpc_error(-4, "Not solvable pre-selected input COutPoint(%s, %s)" % (ext_utxo["txid"][0:10], ext_utxo["vout"]), wallet.fundrawtransaction, raw_tx)
 
         # Error conditions
-        assert_raises_rpc_error(-5, "'not a pubkey' is not hex", wallet.fundrawtransaction, raw_tx, solving_data={"pubkeys":["not a pubkey"]})
-        assert_raises_rpc_error(-5, "'01234567890a0b0c0d0e0f' is not a valid public key", wallet.fundrawtransaction, raw_tx, solving_data={"pubkeys":["01234567890a0b0c0d0e0f"]})
+        assert_raises_rpc_error(-5, 'Pubkey "not a pubkey" must be a hex string', wallet.fundrawtransaction, raw_tx, solving_data={"pubkeys":["not a pubkey"]})
+        assert_raises_rpc_error(-5, 'Pubkey "01234567890a0b0c0d0e0f" must have a length of either 33 or 65 bytes', wallet.fundrawtransaction, raw_tx, solving_data={"pubkeys":["01234567890a0b0c0d0e0f"]})
         assert_raises_rpc_error(-5, "'not a script' is not hex", wallet.fundrawtransaction, raw_tx, solving_data={"scripts":["not a script"]})
         assert_raises_rpc_error(-8, "Unable to parse descriptor 'not a descriptor'", wallet.fundrawtransaction, raw_tx, solving_data={"descriptors":["not a descriptor"]})
         assert_raises_rpc_error(-8, "Invalid parameter, missing vout key", wallet.fundrawtransaction, raw_tx, input_weights=[{"txid": ext_utxo["txid"]}])