Design Multi-Signature Wallet - System Design | WinJob

Problem Statement: Enterprise Multi-Signature Wallet

Design a Gnosis Safe / BitGo / Fireblocks-class multi-signature wallet platform where organizations deploy smart contract Safes, coordinate off-chain signatures, and execute only after M-of-N approval with mandatory simulation and audit. This section focuses on problem during the understanding phase.

Mechanism

Gnosis Safe–class smart contract wallet where M-of-N owners must approve before execution
Off-chain coordination layer stores pending SafeTransaction hashes and collected EIP-712 signatures
Relayer or executor service pays gas only after threshold signatures are assembled
Separate control plane (orgs, policies) from on-chain Safe singleton per chain

Quantified anchors

Target: 12k organizations, 180k deployed Safes, $24B assets under control
Proposal SLA: 99.95% signature collection UI availability; execution broadcast p99 < 90s

Failure drills (problem)

Treating EOAs as signers without hardware binding
Skipping nonce alignment between Safe and executor wallet

Interview checkpoints

Distinguish multi-sig wallet from custodial omnibus in one sentence
Name actors: owner, proposer, relayer, chain

Staff+ extensions (problem)

Tie metrics to treasury payroll windows and DAO governance calendars
Reference EIP-712 domain separation whenever interviewer mentions replay attacks
Offer chaos test: revoke relayer key mid-flight without accepting partial executions

Invariants for multi-sig

Hash invariant: executed calldata must match simulated safeTxHash and policy_snapshot_id.
Threshold invariant: relayer refuses broadcast until distinct owner signatures ≥ threshold.
Nonce invariant: off-chain pending queue never lags on-chain Safe nonce by more than one.

Depth note A.1: Gnosis Safe–class smart contract wallet where M-of-N owners must approve before execution directly affects signature aggregation latency, relayer gas budget, and audit export completeness for problem.

Depth note A.2: Off-chain coordination layer stores pending SafeTransaction hashes and collected EIP-712 signatures directly affects signature aggregation latency, relayer gas budget, and audit export completeness for problem.

Depth note A.3: Relayer or executor service pays gas only after threshold signatures are assembled directly affects signature aggregation latency, relayer gas budget, and audit export completeness for problem.

Depth note A.4: Separate control plane (orgs, policies) from on-chain Safe singleton per chain directly affects signature aggregation latency, relayer gas budget, and audit export completeness for problem.

javaOne Dark Pro

1 public final class MultiSigproblem1Gate {
2   public boolean canExecute(int sigCount, int threshold, String simHash, String policyHash) {
3     return sigCount >= threshold && simHash.equals(policyHash);
4   }
5 }

pythonOne Dark Pro

1 @dataclass(frozen=True)
2 class MultiSigproblem1Proposal:
3     safe_id: str
4     nonce: int
5     safe_tx_hash: str
6     idempotency_key: str

typescriptOne Dark Pro

1 export function multiSigIdempotencyKey(orgId: string, clientRef: string): string {
2   return `multisig:${orgId}:${clientRef}`;
3 }

Why interviewers care

Multi-Signature Wallet interviews reward crisp scope, explicit trade-offs, and failure stories—not generic microservice diagrams.

Interview checkpoint

Name one failure story for Problem Statement: Enterprise Multi-Signature Wallet that proves you understand real outages, not happy-path diagrams.

Key Highlights

•Gnosis Safe–class smart contract wallet where M-of-N owners must approve before execution
•Off-chain coordination layer stores pending SafeTransaction hashes and collected EIP-712 signatures
•Relayer or executor service pays gas only after threshold signatures are assembled
•Separate control plane (orgs, policies) from on-chain Safe singleton per chain

1	public final class MultiSigproblem1Gate {
2	public boolean canExecute(int sigCount, int threshold, String simHash, String policyHash) {
3	return sigCount >= threshold && simHash.equals(policyHash);
4	}
5	}

1	@dataclass(frozen=True)
2	class MultiSigproblem1Proposal:
3	safe_id: str
4	nonce: int
5	safe_tx_hash: str
6	idempotency_key: str

1	export function multiSigIdempotencyKey(orgId: string, clientRef: string): string {
2	return `multisig:${orgId}:${clientRef}`;
3	}