trim-psbt

This is a tool to trim Bitcoin PSBTs (Partially Signed Bitcoin Transactions) down to a smaller size by removing unnecessary info.

Who is this for?

Only me. Unless you can audit the code (including the changes I made in the python libraries copied from f469-disco), you should not use this. It could maliciously alter the PSBT (to send your coins to me, for example).

How do I use it?

With your base64-encoded PSBT in a file, run:

$ ./trim_psbt.py < my-psbt.txt > trimmed-psbt.txt

What does it remove?

For each input that has both non_witness_utxo and witness_utxo input data, it will remove the non_witness_utxo.

Why?

My PSBT use case is offline signing via printed QR codes. The non_witness_utxo can be huge, and is only there to work around a minor security issue.

Security issue? What?

See Trezor's blog and the Bitcoin Core response.

As long as you don't sign the same UTXOs multiple times, you are not vulnerable.