Architecture

The following diagram shows an FHEVM-coprocessor that is integrated alongside an existing host blockchain.

mermaid

graph LR;
    dApp[dApp]
    fhevmjs[fhevmjs]
    Host(((Host Blockchain)))
    Coprocessor(Coprocessor)
    Gateway(Gateway)
    DA[(DA)]
    TKMS[TKMS]

    dApp-- uses ---fhevmjs
    fhevmjs-- Host Blockchain API ---Host
    Host-- P2P ---Coprocessor
    Host <--> |Host Blockchain API| Gateway
    fhevmjs-- Reencrypt API---Gateway
    fhevmjs-- Inputs API ---Gateway
    Gateway-- TKMS txns, events ---TKMS
    Gateway-- Inputs API ---Coprocessor
    Coprocessor-- DA API ---DA

An important note to point out is that the Coprocessor is an offchain component. It contains the following sub-components:

host blockchain full node that executes all blocks on the host blockchain
an executor that does FHE computation
a local database for storing FHE ciphertexts

Essentially, as the Coprocessor executes blocks and when an FHE operation is detected, the executor sub-component would actually execute the FHE computation and load/store FHE ciphertexts from the local database (and the DA). For more on execution, please look at Symbolic Execution and FHE Computation.

The Data Availability (DA) is a publicly-verifiable database that is a mirror of the local Coprocessor database. The reason for having is to allow anyone to verify the behaviour of the Coprocessor by examining the results it posts to it.

The Gateway is responsible for handling input verification, decryption and reencryption and host blockchain validator set updates, all via/in the KMS.