Unable to decode serialized TxOut

[ikripaka]

There is an issue in serialization of TxOut, we're unable to decode it after serialization.
The problem lyes in the simplicityhl::elements::encode::serialize.
For unblinding it misses Rangeproof inside. For some reason it isn't serialized inside.
TxOut contains TxOutSecrets inside

rust-elements/src/transaction.rs

Line 703 in 2d94f5d

pub struct TxOut {

, but TxOutWitness has its own serialization

rust-elements/src/transaction.rs

Line 653 in 2d94f5d

impl_consensus_encoding!(TxOutWitness, surjection_proof, rangeproof);

while TxOut just truncates it

rust-elements/src/transaction.rs

Line 719 in 2d94f5d

impl Encodable for TxOut {

.

Here is a quick code snippet to test it:

use std::time::Duration;
        use simplicityhl::elements::{ Transaction, TxOut,};
        use simplicityhl::elements::bitcoin::secp256k1;
        use simplicityhl::elements::encode;
        
        pub const PUBLIC_SECRET_BLINDER_KEY: [u8; 32] = [1; 32];
        let secret_key = SecretKey::from_slice(&PUBLIC_SECRET_BLINDER_KEY).unwrap();

        
        let tx_id = "8e12b0c994293d15b7f43abaeb6c119ce3612ff00246b7ae9079dca90a35031f";
        let url = format!("https://blockstream.info/liquidtestnet/api/tx/{}/hex", tx_id);
        let client = reqwest::blocking::Client::builder()
            .timeout(Duration::from_secs(10))
            .build()
            .unwrap();
        let tx_hex = client
            .get(&url)
            .send()
            .unwrap()
            .error_for_status()
            .unwrap()
            .text()
            .unwrap();
        
        let transaction: Transaction = encode::deserialize(&hex::decode(&tx_hex).unwrap()).unwrap();
        let tx_out_from_reqwest = transaction.output[0].clone();
        assert!(tx_out_from_reqwest.unblind(secp256k1::SECP256K1, secret_key).is_ok());
        
        let tx_out_from_request_serialized = encode::serialize(&tx_out_from_reqwest);
        let tx_out_from_request_deserialized: TxOut = encode::deserialize(&tx_out_from_request_serialized).unwrap();
        
        assert!(tx_out_from_request_deserialized.unblind(secp256k1::SECP256K1, secret_key).is_ok());

[apoelstra]

Can you post a reproduction that only uses rust-elements?

[apoelstra]

Oh, I see, the issue is that if you directly encode/decode a TxOut it does not include the TxOutWitness. You have to encode/decode this separately, beacuse it appears in a separate part of the transaction.

This is an unfortunate footgun but it sorta falls out of the existing encoding trait. When we move to bitcoin-consensus-encoding I'll try to make the API for this better. Probably we want a separate TxOutWithoutWitness type which isn't really usable until the users finds a witness somewhere.