FHE 101 (Plain Language)

Fully Homomorphic Encryption lets a smart contract operate on encrypted values without revealing them on-chain.

Key ideas

• Encrypted values are bound to a contract and a user.

• Input proofs show the encrypted input matches the expected contract + signer.

• Permissions are required to decrypt results.

The 3 permissions you will see

• FHE.allowThis(value) lets the contract operate on the ciphertext later.

• FHE.allow(value, user) lets a user decrypt.

• FHE.allowTransient(value, contract) grants one-transaction permission (useful for multi-contract flows).

Public decryption

Some examples opt in to public decryption using FHE.makePubliclyDecryptable. This is only safe if the value is meant to be public after an on-chain proof step.

Typical flow

1. User encrypts input off-chain (bound to contract + user)

2. Contract verifies the input proof and stores the ciphertext

3. Contract grants permissions (allowThis / allow)

4. Later, user or authorized party decrypts