User signing the transaction and the gas station signer cannot be the same.

[adriansanchezsequeira-iota]

Gas Station Transfer Issue Case

Problem Description

User signing the transaction and the gas station signer cannot be the same.

Invalid user signature: Expect 1 signer signatures but got 2

Root Cause Analysis

From the gas station logs, we can see that when the transfer back operation is executed:

1. The transaction sender is the same address as the gas station sponsor
2. Both the user and gas owner correspond to the same wallet address

This creates a special edge case where:

• The user signing the transaction is the same as the gas sponsor
• The gas station code adds both sponsor_sig and user_sig to the transaction
• Both signatures are identical because they come from the same keypair
• The IOTA validator rejects the transaction because it expects 1 signature but receives 2 identical signatures

Technical Details

In the gas station Rust code (gas_station_core.rs):

let tx = Transaction::from_generic_sig_data(tx_data, vec![sponsor_sig, user_sig]);

When sponsor_sig and user_sig are identical (same keypair), this creates a duplicate signature issue.

Test Scenario

The failing test sequence:

1. Mint NFT with User A (works)
2. Transfer NFT from User A to User B (works)
3. Transfer NFT back from User B to User A (fails)

The issue occurs because:

• User B corresponds to the same address as the gas station sponsor wallet
• When User B tries to sign a transaction, it creates a duplicate signature situation

Current Status

• All basic operations (mint, resolve, forward transfer) work correctly
• The issue only affects scenarios where the user and gas sponsor are the same address

Recommended Solutions

1. Gas Station Code Fix: The gas station should detect when the user and sponsor are the same and only add one signature

Impact

This is a specific edge case that occurs when the user wallet is the same as the gas station sponsor wallet.