Fhenix Introduction

Overview

Fhenix brings confidentiality to smart contracts using Fully Homomorphic Encryption (FHE). Public blockchains expose everything — every transaction, balance, and contract interaction is visible to anyone. FHE lets computation run directly on encrypted data: the chain never sees raw inputs or outputs, only encrypted values, yet results are still valid when an authorized party decrypts them.

CoFHE (Coprocessor for FHE) is how Fhenix makes this practical. It is an FHE coprocessor that attaches to existing blockchains, so confidentiality becomes "just another Solidity feature":

• No migration — deploy to the chains you already use, not a dedicated FHE L1.
• Familiar code — contracts pass around lightweight handles (references to ciphertexts), not the ciphertexts themselves, so Solidity reads normally.
• No cryptography to implement — heavy FHE math runs offchain on the CoFHE server. Your contract calls FHE.add; CoFHE does the rest.
• Trust-minimized decryption — no single party holds the key; a Threshold Network decrypts via multi-party computation (MPC), gated by signed permits.

The core lifecycle: encrypt → compute → decrypt

Every CoFHE app follows the same three phases:

1. Encrypt (client-side) — Plaintext is encrypted in the client with @cofhe/sdk, bundled with a zero-knowledge proof (zkPoK) that the input is well-formed, and submitted. The chain only ever receives an encrypted handle.
2. Compute (onchain handle, offchain math) — The contract uses FHE.sol on handles (add, lt, select…) as if they were ordinary numbers. Each op deterministically derives a new result handle and is recorded onchain; the CoFHE server independently computes the matching ciphertext offchain. Nothing returns to the contract, and plaintext is never exposed.
3. Decrypt (optional, gated by permits) — An authorized user presents a signed permit. The Threshold Network decrypts via MPC — either re-encrypting the value so only that user can read it (for display, decryptForView), or returning a verifiable plaintext + signature for onchain use (decryptForTx).