fhevm-solidity/docs/getting_started/overview.md

What is fhEVM

Introduction

There used to be a dilemma in blockchain: keep your application and user data on-chain, allowing everyone to see it, or keep it privately off-chain and lose contract composability.

fhEVM is a technology that enables confidential smart contracts on the EVM using Fully Homomorphic Encryption (FHE).

Thanks to a breakthrough in FHE, Zama’s fhEVM makes it possible to run confidential smart contracts on encrypted data, guaranteeing both confidentiality and composability with:

• End-to-end encryption of transactions and state: Data included in transactions is encrypted and never visible to anyone.
• Composability and data availability on-chain: States are updated while remaining encrypted at all times.
• No impact on existing dapps and state: Encrypted state co-exists alongside public one, and doesn't impact existing dapps.

Main features

• Solidity integration: fhEVM contracts are simple solidity contracts that are built using traditional solidity toolchains.
• Simple developer experience: Developers can use the euint data types to mark which part of their contracts should be private.
• Programmable privacy: All the logic for access control of encrypted states is defined by developers in their smart contracts.
• High precision encrypted integers : Up to 256 bits of precision for integers -Full range of Operators : All typical operators are available: +, -, *, /, <, >, ==, …
• Encrypted if-else conditionals: Check conditions on encrypted states
• On-chain PRNG: Generate secure randomness without using oracles
• Configurable decryption: Threshold, centralized or KMS decryption
• Unbounded compute depth: Unlimited consecutive FHE operations

Use cases

• Tokenization: Swap tokens and RWAs on-chain without others seeing the amounts.
• Blind auctions: Bid on items without revealing the amount or the winner.
• On-chain games: Keep moves, selections, cards, or items hidden until ready to reveal.
• Confidential voting: Prevents bribery and blackmailing by keeping votes private.
• Encrypted DIDs: Store identities on-chain and generate attestations without ZK.
• Private transfers: Keep balances and amounts private, without using mixers.