Aptos brings encrypted mempool to mainnet

Aptos activated its optional Encrypted Mempool on mainnet on Oct. 12, letting users hide transaction contents while validators decide their order. The Aptos announcement says the feature is designed to make it harder for bots to exploit visible pending trades. It encrypts each transaction’s payload before submission, then decrypts it after the block is finalized.

What can validators see before a block is final?

When a user opts in, the transaction’s function and arguments are encrypted on the client. The sender’s address and gas fee remain visible. Aptos says its validators jointly generate an encryption key for each epoch, the network period during which the validator set remains fixed.

The encrypted transaction enters the mempool, where pending transactions wait for a block. The block leader proposes an order without seeing the encrypted payload. That sequence matters because a bot that cannot read a pending trade cannot as easily place its own trade ahead of it or on either side of it—a pattern known as a sandwich attack. The order is like a sealed set of instructions that gets arranged before it is opened.

Who decrypts the transactions, and when?

After validators reach consensus on a block, they collectively reconstruct the decryption key and reveal the payloads included in that block. Transactions then execute, and their contents are recorded onchain. Aptos says no single validator can decrypt a pending transaction; decryption requires the same stake-weighted threshold used to finalize blocks.

The approach puts ordering and decryption in the hands of the chain’s existing validators. That means users rely on the validator set they already rely on for consensus, rather than a separate decryption committee. Aptos says a batched threshold encryption scheme lets validators decrypt a whole block with constant-size communication per validator, regardless of batch size.

What does the launch change for users and developers?

Encryption is optional for each transaction, so users need a compatible wallet or application to submit one. Aptos says its TypeScript SDK from version 7.0.0 can fetch the current epoch key, encrypt the payload and submit it; existing Move smart contracts need no changes. Petra is the first wallet to offer encryption in its signing flow, while Aptos says the Decibel perpetuals exchange plans to use the feature for orders.

The launch gives Aptos users a protocol-level option to keep transaction details private until ordering is fixed. Its protection applies to the encrypted payload; the sender and fee remain visible. Aptos reports roughly 20 milliseconds of added latency per block in 50-node benchmarks. The next practical measure is adoption: how many wallets and applications support opt-in encrypted transactions.

References

• Aptos announcement — aptosnetwork.com