[500 SigmaUSD] Distributed signatures support

[greenhat]

References:
EIP-11
Improved distributed signatures

New code should be in prover::multi_sig module.

Generate commitments

fn generate_commitments(tx_context: TransactionContext, state_context: &ErgoStateContext) -> Result<TransactionHintsBag, _> function should be an equivalent of wallet/generateCommitments node API call, see implementation at https://github.com/ergoplatform/ergo/blob/95139ec990fc91f8f4c70a61468edf8834143329/ergo-wallet/src/main/scala/org/ergoplatform/wallet/interpreter/ErgoProvingInterpreter.scala#L182-L222
TransactionHintsBag type should be an equivalent of https://github.com/ergoplatform/ergo/blob/95139ec990fc91f8f4c70a61468edf8834143329/ergo-wallet/src/main/scala/org/ergoplatform/wallet/interpreter/TransactionHintsBag.scala#L5

Extract hints from signed(invalid) transaction

fn extract_hints(tx_context: TransactionContext, state_context: &ErgoStateContext, real_secrets_to_extract: Vec<SigmaBoolean>, simulated_secrets_to_extract: Vec<SigmaBoolean>) -> Result<TransactionHintsBag, _> should be an equivalent of script/extractHints node API call, see implementation at https://github.com/ergoplatform/ergo/blob/95139ec990fc91f8f4c70a61468edf8834143329/ergo-wallet/src/main/scala/org/ergoplatform/wallet/interpreter/ErgoProvingInterpreter.scala#L224-L263

Hints support in prover and tx signing

• Check how hints are used in prover and implement the missing parts compared to the Scala reference implementation at https://github.com/ScorexFoundation/sigmastate-interpreter/blob/455d4a3b5a82eec9301be89019d8ea675386474a/sigmastate/src/main/scala/sigmastate/interpreter/ProverInterpreter.scala#L68-L103
• add tx_hints: TransactionHintsBag parameter to Wallet::sign_* methods and pass it down to prover (as HintsBag);

Wasm API.

• Expose TransactionHintsBag type via wrapper;
• Add tx_hints: TransactionHintsBag parameters to Wallet::sign_* methods;
• Expose generate_commitments and extract_hints (passing serialized SigmaBooleans) functions.

Testing.

• implement test scenarios from https://github.com/ScorexFoundation/sigmastate-interpreter/blob/prepare-v5.0-evaluator/sigmastate/src/test/scala/sigmastate/utxo/DistributedSigSpecification.scala
• tests for generate_commitments should be implemented after https://github.com/ScorexFoundation/sigmastate-interpreter/blob/455d4a3b5a82eec9301be89019d8ea675386474a/sigmastate/src/test/scala/sigmastate/utxo/ProverSpecification.scala#L17-L58

[sahandzou]

I will take it.

[greenhat]

@sahandzou I added requirements and implementation details in the description. Please keep in mind that I'm doing AtLeast implementation in #377 which makes a lot of small changes in sigma protocol implementation (see prover.rs file). I'd suggest you start your branch on top of mine. Feel free to make a draft PR and ask any questions during the process.

EDIT: Or alternatively you can branch from develop and start drafting prover::multi_sig module and then rebase after I merge #377 which I expect to happen early next week.

[sahandzou]

thanks.

[greenhat]

@sahandzou Build and tests are green in my #377 in case you want to branch off of it.

[sahandzou]

UPDATE: multi-sig test with two signers passed!

[greenhat]

The bounty is sent. Thank you!