Miden Multisig Client

High-level Rust SDK built on top of miden-client for private multisignature workflows on Miden. The crate wraps the on-chain multisig contracts plus Guardian coordination so you can:

• create multisig accounts, register them with a GUARDIAN, and keep state off-chain,
• propose, sign, and execute transactions with threshold enforcement,
• fall back to offline SwitchGuardian workflows when connectivity is limited,
• export/import proposals as files for sharing using side channels,

How Private Multisigs & GUARDIAN Work

Miden multisig accounts store their authentication logic on-chain, but their state (signers, metadata, proposals) is kept private. GUARDIAN acts as a coordination server:

1. A proposer pushes a delta (transaction plan) to Guardian. GUARDIAN tracks who signed and emits an ack signature once the threshold is met.
2. Cosigners fetch pending deltas, verify details locally, sign the transaction summary, and push signatures back to GUARDIAN.
3. Once ready, any cosigner builds the final transaction using all cosigner signatures + the GUARDIAN ack, executes it on-chain.

Installation

Add the crate to your workspace (already available in this repo). From another project:

[dependencies]
miden-multisig-client = { git = "https://github.com/OpenZeppelin/guardian", package = "miden-multisig-client" }

Quick Start

use miden_client::rpc::Endpoint;
use miden_multisig_client::{MultisigClient, TransactionType};
use miden_objects::{Word, account::AccountId};

# async fn example() -> anyhow::Result<()> {
let signer1: Word = /* your RPO Falcon commitment */ Word::default();
let signer2: Word = Word::default();

let mut client = MultisigClient::builder()
    .miden_endpoint(Endpoint::try_from("http://localhost:57291")?)
    .guardian_endpoint("http://localhost:50051")
    // Directory where the underlying miden-client SQLite store will live
    .account_dir("/tmp/multisig")
    // Generate a new Falcon keypair for GUARDIAN authentication (builder can also accept your own key)
    .generate_key()
    .build()
    .await?;

let account = client.create_account(2, vec![signer1, signer2]).await?;
println!("Account registered on GUARDIAN endpoint: {}", client.guardian_endpoint());
# Ok(())
# }

Configuration

Beyond the endpoints and the account directory, the builder carries three optional configuration surfaces. The cross-SDK reference, including the TypeScript equivalents, is docs/MULTISIG_SDK.md.

Miden node RPC (rpc_config)

RpcConfig sets the per-request gRPC deadline and the retry budget for idempotent node reads. The policy wraps the node client itself, so every read this SDK or the underlying miden-client issues (syncs, account, note, and block lookups) is covered.

use miden_multisig_client::{RpcConfig, RpcRetryPolicy};

let rpc_config = RpcConfig::new()
    .with_timeout_ms(15_000)?
    .with_retry_policy(RpcRetryPolicy::new(3));

let mut client = MultisigClient::builder()
    .miden_endpoint(Endpoint::devnet())
    .guardian_endpoint("http://localhost:50051")
    .account_dir("/tmp/multisig")
    .rpc_config(rpc_config)
    .generate_key()
    .build()
    .await?;

The defaults are a 10-second deadline and two total attempts (one classified, jittered retry); RpcRetryPolicy::new(1) opts out. Rate limiting and transport-shaped connection failures retry. Permanent failures (invalid argument, not found, authentication, TLS or certificate problems, invalid endpoint) return immediately without consuming the budget, and once the budget is exhausted the final upstream error is returned unchanged.

Transaction submission is never retried under any configuration: a submission whose outcome is unknown could execute twice if re-sent. The same policy covers the note transport, where fetches and stream establishment retry but note sends are never retried in-call (the client's relay outbox re-sends undelivered notes on later syncs).

Note transport endpoint (note_transport_endpoint)

Private notes are relayed through a note transport service that is separate from the node RPC. The testnet and devnet presets derive the transport endpoint automatically; a custom node endpoint has no derivable transport service, so private-note relay stays disabled until this is set explicitly.

let mut client = MultisigClient::builder()
    .miden_endpoint(Endpoint::try_from("https://my-node.internal:57291")?)
    .note_transport_endpoint("https://my-transport.internal")
    .guardian_endpoint("http://localhost:50051")
    .account_dir("/tmp/multisig")
    .generate_key()
    .build()
    .await?;

Remote prover (prover_config)

ProverConfig overrides the remote prover endpoint and the proof retry policy. Without it, the devnet and testnet presets use their public provers and every other endpoint proves locally. A custom URL must be absolute HTTP(S) and never falls back to a default endpoint. Remote proving gets two total attempts by default and local proving is never retried; retries apply only to transient proof failures, so transaction execution, submission, local state application, and GUARDIAN calls each run once.

use miden_multisig_client::{ProverConfig, ProverRetryPolicy};

let prover_config = ProverConfig::new()
    .with_url("https://prover.example")?
    .with_retry_policy(ProverRetryPolicy::new(4));

Core Workflow Examples

Propose ➜ Sign ➜ Execute

use miden_multisig_client::TransactionType;
use miden_objects::account::AccountId;

let recipient = AccountId::from_hex("0x7b7b7b7a7b7b7b017b7b7b7b7b7b7b")?;
let faucet = AccountId::from_hex("0x7c7c7c7c7c7c7c017c7c7c7c7c7c7c")?;
let tx = TransactionType::transfer(recipient, faucet, 1_000);

// P2ID notes are public by default. For a private note (only its hash is
// published on chain; the recipient needs the note shared out-of-band) use
// `transfer_with_note_type`. `NoteType` is re-exported from `miden_protocol::note`.
use miden_protocol::note::NoteType;
let tx = TransactionType::transfer_with_note_type(recipient, faucet, 1_000, NoteType::Private);

// Proposer creates the delta on GUARDIAN
let proposal = client.propose_transaction(tx).await?;

// Second cosigner lists available proposals and signs the matching one
let proposals = client.list_proposals().await?;
let to_sign = proposals
    .iter()
    .find(|p| p.id == proposal.id)
    .expect("proposal not found");
client.sign_proposal(&to_sign.id).await?;

// Once threshold is met, any cosigner can execute
client.execute_proposal(&proposal.id).await?;

Recovering From a Dead Transaction (Abandon)

If execute_proposal dies after guardian approval (RPC submit failure, prover timeout, crash), the approved candidate keeps the account locked on GUARDIAN. Record an abandon intent and poll for the resolution:

use miden_multisig_client::{AbandonRequestState, AbandonStatus};

// The nonce the proposal was pushed with (committed account nonce + 1).
let state = client.abandon_candidate(nonce).await?;
assert_eq!(state, AbandonRequestState::Pending);

// The guardian's worker confirms over a short quarantine (typically well
// under a minute) that the transaction did not land, then releases the
// account.
loop {
    match client.abandon_status(nonce).await? {
        AbandonStatus::Waiting => tokio::time::sleep(Duration::from_secs(5)).await,
        AbandonStatus::Abandoned => break,           // account released
        AbandonStatus::Landed => break,              // tx landed after all
        AbandonStatus::Unexpected => anyhow::bail!("unexpected candidate state"),
    }
}

Fallback to Offline (if GUARDIAN unavailable)

If the GUARDIAN endpoint can’t be reached, the SDK can produce an offline proposal only for SwitchGuardian transactions:

use miden_multisig_client::{ProposalResult, TransactionType};

let tx = TransactionType::switch_guardian("https://new-guardian.example.com", new_guardian_commitment);
match client.propose_with_fallback(tx).await? {
    ProposalResult::Online(p) => {
        println!("Proposal {} is live on GUARDIAN", p.id);
    }
    ProposalResult::Offline(exported) => {
        let path = "proposal_offline.json";
        std::fs::write(path, exported.to_json()?)?;
        println!("GUARDIAN unavailable. Share {} with cosigners, collect signatures, then run `execute_imported_proposal` once ready.", path);
    }
}

Fully Offline Signing and Execution

use miden_multisig_client::TransactionType;

let tx = TransactionType::switch_guardian("https://guardian.example.com", new_guardian_commitment);
let mut exported = client.create_proposal_offline(tx).await?;

// Cosigner signs locally
client.sign_imported_proposal(&mut exported).await?;
std::fs::write("proposal_signed.json", exported.to_json()?)?;

// Once enough signatures are collected offline:
client.execute_imported_proposal(&exported).await?;

Listing Notes

List all notes that are currently consumable by the loaded account:

let notes = client.list_consumable_notes().await?;
for note in notes {
    println!("Note {} has {} assets", note.id.to_hex(), note.assets.len());
}

List notes from a specific faucet with a minimum amount filter:

use miden_multisig_client::NoteFilter;

let faucet = AccountId::from_hex("0x7c7c7c7c7c7c7c017c7c7c7c7c7c7c")?;
let filter = NoteFilter::by_faucet_min_amount(faucet, 5_000);
let spendable = client.list_consumable_notes_filtered(filter).await?;

Custom Proposal Types

GUARDIAN accepts any non-empty proposal_type, so an integration can propose a transaction the SDK does not model (an agglayer bridge note, an arbitrary dApp transaction) under its own label. The SDK normalizes the label to lowercase snake_case (trims and lowercases it, then requires [a-z0-9_]+ — the same shape as built-in labels like add_signer), so "B2Agg" becomes b2agg and "add signer" / "add-signer" are rejected. Such a proposal buckets to TransactionType::Custom and keeps its normalized label in ProposalMetadata.proposal_type. It can be listed, signed, and exported/imported through the normal flow, but the generic SDK cannot build its on-chain transaction — the integration owns that recipe and drives execution.

use miden_client::Serializable;
use miden_multisig_client::{build_p2id_transaction_request, generate_salt};
use miden_protocol::note::NoteType;

// Producer: build a transaction and propose it under a custom label.
let salt = generate_salt();
let mut request = build_p2id_transaction_request(
    account.inner(), recipient, vec![asset], NoteType::Public, salt, std::iter::empty(),
)?;
let proposal = client.propose_custom_transaction(&request.to_bytes(), "b2agg").await?;

// Cosigners review and sign through the usual list/sign flow.

// Producer (once threshold is met): bind-check the request, fetch the validated
// advice, inject it into the request, and submit. `prepare_custom_execution`
// verifies the request against the signed commitment *before* the GUARDIAN ack.
let advice = client.prepare_custom_execution(&proposal.id, &request.to_bytes()).await?;
request.advice_map_mut().extend(advice);
client.submit_transaction(request).await?;

The integration keeps only its own recipe (build inputs + salt) so it can reproduce the exact transaction at execute time — the SDK does not store the serialized request. The binding check guarantees the rebuilt transaction matches the commitment the cosigners signed.

Consume-notes metadata versions

consume_notes proposals come in two metadata shapes. The discriminator is the consume_notes_metadata_version field on the wire.

• v1 (legacy) — consume_notes_metadata_version absent on the wire. The proposal carries only note_ids; the verifier rebuilds the transaction request by fetching each note from its own local Miden store. If the verifier does not have the note locally (cursor advanced past the block, store was wiped, private-note transport pruned the blob), verification fails with MultisigError::LegacyConsumeNotesNoteMissing and the cosigner cannot sign. This is the failure tracked by issue #229.
• v2 (self-contained) — consume_notes_metadata_version: 2 plus a consume_notes_notes array carrying base64-serialized Note bytes aligned by index with note_ids. Verification rebuilds the request from the embedded notes alone — no local-store read, no network call. This restores the same "rebuild from signed metadata" invariant every other proposal type already satisfied (and that audit finding M-08 remediated for p2id).

Proposal creation always emits v2 starting with this release; the proposer is the one party guaranteed to hold the notes locally. The per-proposal v2 payload is capped at MAX_CONSUME_NOTES_METADATA_BYTES (256 KiB) and the size is enforced at creation time so the failure surfaces to the proposer before any signature collection begins.

Error taxonomy

All four errors below carry a stable, cross-SDK string code via MultisigError::code(). The TS SDK exposes the same identifiers as Error.code.

Cut-over policy

The legacy-consume-notes Cargo feature (default-on in this transitional release) gates whether the crate accepts v1 metadata for verification. A future cut-over release will ship with default = [], at which point v1 proposals are refused with UnsupportedMetadataVersion { found: None } on every code path. Deployments should drain or re-propose any v1 consume_notes proposals in flight before upgrading past the cut-over client version. Tracked by spec 006-consume-notes-metadata.

Demo CLI

Run the Terminal UI demo in examples/demo, which exercises the same APIs for account management, note listing, proposal signing, and offline export/import.

Contributions and bug reports are welcome!