Aptos rolls out Encrypted Mempool to curb frontrunning, sandwich attacks

Layer-1 blockchain Aptos has launched an optional new feature that could help shield traders from attacks involving maximal extractable value (MEV), including frontrunning and sandwich attacks.

On Monday, Aptos said its Encrypted Mempool feature is now live on its mainnet, allowing users to opt in to keep pending transactions encrypted until their block ordering is finalized. Aptos said the feature was built for institutions submitting large transactions to the chain, traders wanting to avoid MEV risk, AI agents and builders.

“When you send a transaction on any major chain today, anyone watching the network can see the details before it executes, the function you’re calling, the assets and amounts involved, and the contracts you’re interacting with,” Aptos said. “Bots use that visibility to trade against you or copy your strategy.”

Sandwich attacks, one form of MEV attack, cost Ethereum traders about $60 million over the 12 months through October 2025, according to Cointelegraph’s analysis of EigenPhi data. On Solana, sandwich attacks generated $29.7 million for bots over an 11-month period examined by Bitquery, which identified nearly 6.9 million attacks affecting about 2.2 million wallets.

How Encrypted Mempool works

When a user opts in, a compatible wallet or app encrypts the transaction’s contents on their device before sending it to Aptos. Details such as the assets and amounts involved stay hidden, while the sender’s address and gas fee remain visible.

The encrypted transaction enters the mempool, which is where pending transactions wait to be included in a block. Validators agree on the order of the transactions while being blind to their contents.

Once the ordering is finalized, validators collectively decrypt the transactions, which are then executed and recorded onchain. No single validator can decrypt a pending transaction on its own.

Keeping transaction details hidden until their ordering is fixed can prevent bots from reading pending orders and inserting trades ahead or around them to profit at users’ expense.

The protection comes with added costs and a small delay. Encrypted transactions carry a minimum gas price at twice the network’s base minimum, according to Aptos’ developer documentation. Aptos also said the system adds around 20 milliseconds per block in tests involving 50 nodes, compared to the existing consensus implementation.

Aptos joins other networks offering protection against harmful MEV. Gnosis Chain launched an encrypted mempool using Shutter in July 2024, while Ethereum’s Flashbots Protect routes transactions privately to block builders. Aptos said its distinction is that its existing validators handle both transaction ordering and decryption, rather than relying on a separate decryption committee or trusted builders.