Safe Multisig: Step-by-Step Verification

Engineer/DeveloperSecurity SpecialistOperations & Strategy

Authored by:

Isaac Patka

SEAL | Shield3

Geoffrey Arone

Shield3

Louis Marquenet

Opsek

Pablo Sabbatella

SEAL | Opsek

Dickson Wu

SEAL

Reviewed by:

Piña

Coinspect

engn33r

Hash verification protects against UI compromise attacks where malicious transactions are injected into the signing flow. The goal is to ensure that what you see in the UI matches what your hardware wallet actually signs.

General Signing Guidelines

Basic Rules

Use hardware wallet & back up the seed phrase
Use a separate browser or browser profile for signing to minimize extension/session cross-contamination and reduce attack surface on your primary profile
Secure signing environment: For maximum security, all signing activities should be performed on a dedicated, air-gapped, or hardened device running a secure OS. Using a primary work laptop significantly increases the risk of malware interference.
Verify the address according to the procedures on this page upon joining any multisig
Check transactions you see in the queue - if unclear what the transaction should do and why, don't sign it and ask for explanation
Require "how to check" guide for every transaction
Verify addresses & sums through third party sources (message from fellow multisig co-signer is not sufficient)
Communicate transaction status: Tell other signers whether the transaction can be executed right away or not
Confirm after signing: Communicate once you've checked and signed ("checked, signed, X more required")
Last signer executes: If the transaction can be executed right away, the last signer does it. If they can't execute, communicate with other signers
Re-verify before execution: If executing an already signed transaction, check it as if you were signing it

Key Definitions (EVM)

Domain Hash (EIP-712 domain separator)
Message Hash (raw hash of transaction params)
SafeTxHash (combined domain + message hash)

Recommended Tools

Safe Tx Hashes Util (CLI): Most comprehensive verification tool

✅ Calldata decoding (except in interactive mode), signature verification, risk warnings
✅ Supports all Safe features including nested Safes
⚠️ Requires command line familiarity

OpenZeppelin Safe Utils (Web UI): User-friendly alternative

✅ Simple web interface, calldata verification
❌ Limited features
Does not currently support non-transaction signature verification
Does not warn for risky transaction types
⚠️ May lag behind CLI tool capabilities

Other Tools

Lido Safe TX Hashes Calculation
Cyfrin Safe Hashes RS

1) Transaction Preparation

Use delegated proposer (recommended)
Ensure the transaction is proposed in the Safe API
Record Safe address, network, nonce

2) Simulation Testing

Run Tenderly simulation from Safe UI; verify expected events and transfers
If using a timelock, expect a staged transaction event rather than execution

Tenderly simulation setup

Manual simulation (when needed):

Paste the contract address in the contract field
Paste the calldata from the Safe UI or from the hash verification tool
Specify the Safe address as the From address

Note: For complex batch transactions that include a delegateCall to multisend, manual simulations may not be feasible.

3) Hash & Calldata Verification

Using CLI tool:

./safe_hashes.sh --network [NETWORK] --address [SAFE_ADDRESS] --nonce [NONCE]

The CLI tool pulls the queued transaction from the Safe API for verification. If Safe infrastructure is compromised, it's possible the tool will show a hash that matches the UI, but the transaction is still not what you intend to sign. However, if you also verify the calldata output by the tool, you can be sure you are signing the correct data.

Interactive mode (no Safe API dependency): Use --interactive to enter all transaction details manually. Note that in interactive mode the tool does not decode the calldata, so it's important to perform the calldata verification in step 5.

Using web UI (OpenZeppelin Safe Utils)

Navigate to OpenZeppelin Safe Utils
Enter Safe address (checksummed)
Select network and enter nonce
Review generated hashes and decoded calldata

Important: Both tools require checksummed addresses:

Checksummed address examples

✅ Correct: 0xA79C6968E3c75aE4eF388370d1f142720D498fEC
❌ Incorrect: 0xa79c6968e3c75ae4ef388370d1f142720d498fec
Interactive mode note: In interactive mode the CLI does not decode calldata; be sure to perform the calldata verification in step 5.

4) Hash Comparison

Message Hash on tools must match hardware wallet display
Domain Hash ensures correct Safe
SafeTxHash for nested Safe approvals

5) Calldata Review

Decode calldata (e.g., SwissKnife)
Verify functions, recipients, amounts; watch for risky operations

Tool diversity recommendation

Signers should not all use identical tools. Cross-verify results between multiple tools (CLI and web) for critical operations.

Special Cases: Nested Safes

Use --nested-safe-address and --nested-safe-nonce to verify approveHash flows