Ordering Transactions Without Seeing Them: What Aptos's Encrypted Mempool Means for Fair Execution on Blockchains

What went live

On October 12, 2026, Aptos announced on its official blog that its encrypted mempool was live on mainnet. On a blockchain, transactions wait in a holding area called the mempool before they are finalised. Its contents are usually visible to everyone, so it is possible to spot a large order in advance and insert one's own transaction just before it. An encrypted mempool fixes the order of transactions while their contents are still encrypted, and only decrypts and executes them after that.

How it works

Users encrypt the contents of a transaction (the function called and its arguments) on their own device before sending it. The party that decides block order fixes the order without seeing the contents. After that, the validators (participants who verify transactions) jointly decrypt it. Decryption requires validators holding at least two-thirds of the stake, so a small colluding group cannot read contents early.

Technically, the system decrypts batches of transactions at once, which keeps communication and computation among validators down. In a 50-node test, it added about 20 milliseconds of latency per block compared with normal processing, and blocks were still finalised in under a second. An external audit was carried out in March 2026.

Conditions and limits

Encryption is optional and can be chosen per transaction, and existing smart contracts do not need to change. The first supporting wallet is Petra, and Decibel, a derivatives exchange, has said it plans to use the feature to keep orders confidential.

There are limits. Only the transaction contents are encrypted; the sender, fee-related fields and signature remain visible, and the official documentation states that it is "not full anonymity". Fees are higher: a simple transfer costs about seven times the normal amount in one example. Transaction data becomes public as usual once finalised, so protection covers only the period before finalisation. Some account types cannot use the feature.

Context: MEV and market integrity

Profits from manipulating transaction order are known as MEV and have long been seen as a structural problem in on-chain trading. A Cointelegraph article citing EigenPhi data reports that "sandwich attacks", in which an attacker trades on both sides of someone else's transaction, cost traders on Ethereum about USD 60 million in the year from November 2024 to October 2025. Ethereum also has a draft proposal, EIP-8105, to build an encrypted mempool into the protocol.

In Japan, amendments to the Financial Instruments and Exchange Act passed in July 2026, extending insider-trading rules to crypto-assets and adding market manipulation and similar conduct to the administrative-penalty regime. As trading of tokenised securities and crypto-assets spreads on blockchains, the question of who ensures fair execution, and how, will grow. An encrypted mempool tries to answer part of it through infrastructure design rather than market surveillance.

Business Development Insights

1. Ensuring fair trading through infrastructure design, rather than after-the-fact surveillance, is now a real option. Financial institutions designing trading services for tokenised securities or digital assets on blockchains should add front-running protection to their criteria for choosing a chain.
2. Encryption costs more, so not every transaction needs it. Execution systems that apply it selectively, for example only to large orders or trades with significant price impact, leave room to differentiate as a service.
3. When validators decrypt jointly, how decentralised and reliable they are affects market fairness. Running a validator is shifting from simply verifying transactions to helping uphold market integrity.

Sources

Aptos official blog, "Encrypted Mempool now live on Aptos mainnet" https://aptosnetwork.com/currents/encrypted-mempool-mainnet Aptos developer documentation https://aptos.dev/build/guides/encrypted-pending-transactions Aptos Labs (Medium, Oct 30, 2025) https://medium.com/aptoslabs/aptos-encrypted-mempool-native-transaction-intent-confidentiality-on-aptos-e90da3cfb254 ZKSecurity audit report https://reports.zksecurity.xyz/reports/aptos-encrypted-mempool.md Atarashii Keizai (NEW ECONOMY) https://www.neweconomy.jp/posts/616575 ForkLog https://forklog.com/en/?p=105183 KuCoin Blog https://www.kucoin.com/blog/aptos-encrypted-mempool-goes-live-how-it-could-reduce-mev-attacks Cointelegraph / EigenPhi (Ethereum sandwich attacks) https://cointelegraph.com/research/exclusive-data-from-eigenphi-reveals-that-sandwich-attacks-on-ethereum-have-waned EIP-8105 https://eips.ethereum.org/EIPS/eip-8105 Kumamoto Nichinichi Shimbun (FIEA amendment passed) https://kumanichi.com/articles/2013867 Monolith Law Office (FIEA amendment commentary) https://monolith.law/corporate/fiea-amendment-2026-crypto