Add ability to blind only value in the PSET output #301

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1. apoelstra commented on Oct 14, 2026

   

   apoelstra

   on Oct 14, 2026

   Last edited by apoelstra

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   Yep, concept ACK, though I'm not exactly sure what the API should look like. But we did deliberately design the consensus protocol and PSET so that this should be possible.

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2. KyrylR commented on Oct 20, 2026

   

   KyrylR

   on Oct 20, 2026

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   Opened #302 for the discussion of API

   The implementation there is just to prove that the concept works, I would rewrite it after we align on API itslef
3. KyrylR commented on Oct 20, 2026

   

   KyrylR

   on Oct 20, 2026

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   4. Opened #302 for the discussion of API
   The implementation there is just to prove that the concept works, I would rewrite it after we align on API itslef

       pub fn blind_last_with_modes<C: secp256k1_zkp::Signing, R: RngCore + CryptoRng>(
           &mut self,
           rng: &mut R,
           secp: &secp256k1_zkp::Secp256k1<C>,
           inp_txout_sec: &HashMap<usize, TxOutSecrets>,
           modes: &BTreeMap<usize, BlindingMode>,
       ) -> Result<BTreeMap<CtLocation, (AssetBlindingFactor, ValueBlindingFactor, SecretKey)>, BlindingModeError> { ... }

   #[allow(missing_docs)]
   #[derive(Debug, Clone, Copy, PartialEq, Eq)]
   pub enum BlindingMode {
       ValueOnly,
       AssetAndValue,
   }

   Above are core API choices

   Overall user could provide an empty set and the blinding will happen for both value and asset

   If user wants to value only blind, the user would need to explicitly specify so

   I was not able to avoid re-implementing the blinding (reusing blind last, or something like that)

   Will wait for your feedback
4. apoelstra commented on Oct 22, 2026

   

   apoelstra

   on Oct 22, 2026

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   I would prefer BlindingMode hold a pair of booleans blind_asset and blind_value. All four possibilities are legitimate.

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5. KyrylR commented on Oct 28, 2026

   

   KyrylR

   on Oct 28, 2026

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   6. I would prefer BlindingMode hold a pair of booleans blind_asset and blind_value. All four possibilities are legitimate.

   I have updated the https://github.com/ElementsProject/rust-elements/pull/302/changes (sketch PR)

   Core questions:

   1. Is it Ok to extended the PsetBlindError type or better to create new one?

   2. For refactoring purposes I would move

     if let Some(i) = inp_txout_sec.keys().copied().filter(|&i| i >= self.inputs.len()).min() {
               return Err(PsetBlindError::InputSecretsOutOfRange(i));
           }

        let utxo = input.witness_utxo.as_ref().ok_or(PsetBlindError::MissingWitnessUtxo(i))?;
   
               if let Some(secrets) = inp_txout_sec.get(&i) {
                   if !secrets_open(secp, utxo, secrets) {
                       return Err(PsetBlindError::InputSecretsMismatch(i));
                   }
               }

   into blinding_checks function

   3. What is your take on doing clones (https://github.com/KyrylR/rust-elements/blob/4843dbd6d5b37a9e0b813e7e34566f53ae9d0f99/src/pset/mod.rs#L790)?

   Overall this is it in regard to my questions, if you notice anything else, pls let me know
6. apoelstra commented on Nov 2, 2026

   

   apoelstra

   on Nov 2, 2026

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   1. Yeah, I think it's fine to just extend the error enum. I could be convinced either way about making a new one, so let's just stick with the simple solution.
   2. Yeah, factoring out the sanity checks is a good idea. Arguably, these checks passing should be an invariant of the type. (But it's hard to enforce invarants of this massive map-of-map-of-maps type, so we don't need to worry about that for now.)
   3. This clone seems like the right choice. Would be pretty complicated to get this "rollback on error" behavior without it.

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