`signrawtransactionwithkey` doesn't work with non segwit p2sh scripts

Christewart commented at 8:09 pm on June 10, 2025: contributor

Is there an existing issue for this?

I have searched the existing issues

Current behaviour

I’m attempting to reproduce the transaction specified by AJ Towns that pointed out BitVM bridges with CTV+CSFS for p2sh outputs are vulnerable to theft. You can read more about the topic here.

The TLDR is i’m attempting to sign a p2sh(p2pk) script.

I’ve attempted to create this transaction via the signrawtransactionwithkey RPC. I kept receiving an error saying

{ 'error': 'Unable to sign input, invalid stack size (possibly missing key)'}]}

despite explicitly passing in the public key and redeem script in the prevTxs and keys rpc argument. You can view this here:

https://github.com/Christewart/bitcoin/blob/ae6d4476b730d0909f88405f9a9c08383611a49f/test/functional/feature_bitvmctvcsfs_bridge.py#L48

After wandering through the source code, it seems that there is a disconnect between the Solver and creation of the KeyStore inside of ParsePrevOuts.

The KeyStore attempts to search for the KeyId of the p2sh output script.

The ParsePrevOuts function only adds the KeyId of the redeemScript for p2sh outputs.

I’ve modified the code on my feature branch to add both the keyid of the p2sh redeem script and the keyid of the output script to the keystore, and now I at least get a digital signature produced (rather than Unable to sign input, invalid stack size (possibly missing key)).

https://github.com/Christewart/bitcoin/blob/ae6d4476b730d0909f88405f9a9c08383611a49f/src/rpc/rawtransaction_util.cpp#L251

From a quick glance through rpc_signrawtransactionwithkey.py it seems that p2sh(p2wsh()) is tested, but AFAICT legacy p2sh is not tested.

Expected behaviour

rpc_signrawtransactionwithkey should be able to sign p2pk redeem scripts

Steps to reproduce

Run ./build/test/functional/feature_bitvmctvcsfs_bridge.py on this commit: https://github.com/Christewart/bitcoin/commit/ae6d4476b730d0909f88405f9a9c08383611a49f

and remove this line of code to see the failure:

https://github.com/Christewart/bitcoin/blob/2025-06-07-ctvcsfs-bitvm/src/rpc/rawtransaction_util.cpp#L251

Relevant log output

No response

How did you obtain Bitcoin Core

Compiled from source

What version of Bitcoin Core are you using?

https://github.com/Christewart/bitcoin/commit/ae6d4476b730d0909f88405f9a9c08383611a49f

Operating system and version

Mac

Machine specifications

No response

achow101 commented at 10:00 pm on June 10, 2025: member

Your test has a bug:

0        script_b = script_to_p2sh_script(redeem_script)
1        address = script_to_p2sh(script_b)

address is computed incorrectly. script_to-p2sh is like script_to_p2sh_script in that it takes the redeem script. When you pass it script_b, what you’re really creating is a p2sh(p2sh()) which is invalid. I believe if you modify your test to try to broadcast the transaction, it would fail to validate.

Christewart commented at 6:43 pm on June 11, 2025: contributor

Your test has a bug:
0        script_b = script_to_p2sh_script(redeem_script)
1        address = script_to_p2sh(script_b)
address is computed incorrectly. script_to-p2sh is like script_to_p2sh_script in that it takes the redeem script. When you pass it script_b, what you’re really creating is a p2sh(p2sh()) which is invalid. I believe if you modify your test to try to broadcast the transaction, it would fail to validate.

This is correct. Thank you for pointing that out @achow101 . Much appreciated!

Christewart closed this on Jun 11, 2025

signrawtransactionwithkey doesn’t work with non segwit p2sh scripts #32722