Aptos Activates Encrypted Mempool on Mainnet to Target Front-Running and Sandwich Attacks

On Oct. 12, Aptos activated its opt-in Encrypted Mempool on mainnet, changing what validators can inspect before a block is finalized. Transaction instructions, including function calls and arguments, are encrypted instead of exposed in the mempool; payloads remain concealed until block consensus is finalized.

Sender addresses and fees are still visible. Aptos said the feature is intended to limit information available for front-running and sandwich attacks during transaction ordering.

It is not a fully private transaction system, because key metadata remains public.

Aptos launches an opt-in encrypted mempool on mainnet

Aptos announced that the Encrypted Mempool is live on its mainnet and available on an opt-in basis. It hides transaction payloads until consensus has been completed, a design intended to prevent pending trade details from being used before their ordering is settled.

Front-running generally involves acting on advance knowledge of a pending transaction, while a sandwich attack places trades before and after a target transaction to exploit its expected market effect. Cointelegraph reported on Oct. 13 that Aptos positioned the optional feature for traders, institutions, AI agents and builders seeking protection from those practices.

Validators order encrypted payloads before collective decryption

Transaction payloads are encrypted on the client side. Validators can order transactions without seeing their function calls or arguments, Aptos said, and the network collectively decrypts the payloads only after consensus. Withholding those instructions during ordering is designed to reduce the ability of parties monitoring pending activity to identify and react to them before finalization.

Official Aptos Encrypted Mempool mainnet announcement graphic — Source: Aptos Network

Transaction metadata remains visible

Aptos Improvement Proposal 144 specifies that encrypted transactions are decrypted only after consensus and uses threshold stake-weighted validator voting.

The proposal states that the approach introduces no additional trust assumption beyond Aptos consensus.

The protection nevertheless has defined limits. Sender addresses and transaction fees remain visible, meaning the launch conceals payloads rather than creating full transaction anonymity.

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