Multi-Party-TSS (ECDSA-DKLs23)

Silent Shard uses Multiparty computation (MPC) and enables a set of parties that do not trust each other to jointly compute a secret signing key without being constructed in one place and an ECDSA signature over their secret key shards while not sharing them with any of the involved parties, removing single points of trust.

TSS consists of three stages:

• Distributed Key Generation (DKG),
• Distributed Signature Generation, and
• Proactive Security with Key rotation/refresh.

These functions involve cryptographic computing at the participating nodes of the MPC quorum and exchanges of rounds of messages which ultimately lead to the generation of a valid signature at the requested node. These computing nodes can be any device with sufficient computational and memory capability, including but not limited to smartphones, server nodes, and edge devices. The basic philosophy behind Silent Shard remains that no single device holding the private key can be used to generate signatures and move digital assets. The private key is shared among multiple computing nodes so that no party has any information about the key. Then, in order to generate a signature, the threshold number of devices run a secure two-party computation protocol that generates the signature without revealing anything about the parties' key shares to each other. These devices may or may not be associated with the same person or organization and can be any form factor. Thus, one could use this to create a wallet, sharing the private key between one's mobile and one's laptop, between one's mobile and a VM in the cloud, and so on.

Protocol

• Silent Shard is based on DKLs23 threshold signature scheme
• Enabled by well-chosen correlation + simple new consistency check.
• Blackbox use of UC 2-round 2P-MUL.
• UC secure.

Disclaimer

• The code does not handle network communication security.
• The state struct per request has public and private fields.
• Presignatures should be used only once.
• Proper validating of messages per round is needed.

Crates

dksl23-ll

The library contains a small set of tests. Please look for usual Rust tests in src/dkg.rs and src/dsg.rs

Εxamples (local unit tests with no communication)

• Distributed Key Generation cargo test dkg::dkg2_out_of_2// 2 parties and t=2 cargo test dkg::dkg2_out_of_3// 3 parties and t=2

• Distributed Signatures: cargo test dsg::sign_2_out_of_2 cargo test dsg::sign_2_out_of_3

• Compute presignature only: Run the dsg::sign_2_out_of_* without the last round:

  let mut rng = rand::thread_rng();
  let chain_path = DerivationPath::from_str("m").unwrap();
      let mut parties = dkg(ranks, t)
          .into_iter()
          .take(t as usize)
          .map(|s| State::new(&mut rng, s, &chain_path).unwrap())
          .collect::<Vec<_>>();
  
      let msg1: Vec<SignMsg1> =
          parties.iter_mut().map(|p| p.generate_msg1()).collect();
  
      check_serde(&msg1);
  
      let msg2 = parties.iter_mut().fold(vec![], |mut msg2, party| {
          let batch: Vec<SignMsg1> = msg1
              .iter()
              .filter(|msg| msg.from_id != party.keyshare.party_id)
              .cloned()
              .collect();
          msg2.extend(party.handle_msg1(&mut rng, batch).unwrap());
          msg2
      });
  
      check_serde(&msg2);
  
      let msg3 = parties.iter_mut().fold(vec![], |mut msg3, party| {
          let batch: Vec<SignMsg2> = msg2
              .iter()
              .filter(|msg| msg.from_id != party.keyshare.party_id)
              .cloned()
              .collect();
          msg3.extend(party.handle_msg2(&mut rng, batch).unwrap());
          msg3
      });
  
      check_serde(&msg3);
  
      let pre_signs = parties
          .iter_mut()
          .map(|party| {
              let batch: Vec<SignMsg3> = msg3
                  .iter()
                  .filter(|msg| msg.from_id != party.keyshare.party_id)
                  .cloned()
                  .collect();
  
              party.handle_msg3(batch).unwrap()
          })
          .collect::<Vec<_>>();
  
      check_serde(&pre_signs);
  
      let hash = [255; 32];
  
      let (partials, msg4): (Vec<_>, Vec<_>) = pre_signs
          .into_iter()
          .map(|pre| create_partial_signature(pre, hash))
          .unzip();
  

dkls-wasm-ll

WASM bindings for dkls23-ll.

Build:

Install wasm-pack:

curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh

wasm-pack build -t web wrapper/wasm-ll

Tests:

To run the test install deno:

curl -fsSL https://deno.land/install.sh | sh

deno test -A wrapper/wasm-ll/tests/tests.ts

Articles and links

• DKLs23 https://eprint.iacr.org/2023/765.pdf
• DKG based on Protocol 6.1 https://eprint.iacr.org/2022/374.pdf
• 1 out of 2 Endemic OT Fig.8 https://eprint.iacr.org/2019/706.pdf
• All-but-one OTs from base OTs: Fig.13 and Fig.14 https://eprint.iacr.org/2022/192.pdf
• Generation of sent_seed_list and rec_seed_list values ​​based on Protocol 2.2 Pairwise Randomization dkls23_preprint.pdf
• SoftSpokenOT protocol https://eprint.iacr.org/2022/192.pdf
• Instantiation of SoftSpokenOT based on Fig.10 https://eprint.iacr.org/2015/546.pdf
• Proactive security definition, Section 2 https://www.iacr.org/archive/eurocrypt2006/40040601/40040601.pdf