Arcium Developers Docs - RAG Notes (Local)

Purpose: condensed, query-friendly notes from https://docs.arcium.com/developers/* for debugging ArcInfer.

This is not a copy of the docs; it's a structured extraction with links.

Callback Tracking

Source: https://docs.arcium.com/developers/js-client-library/callback.md

• Confidential computations are multi-step: queue tx -> mempool -> MPC execution -> callback tx.
• You cannot await the queue tx and expect results.
• Use awaitComputationFinalization(provider, computationOffset, program.programId, commitment?).
• This function works by listening for a finalize event over PubSub/websocket (Anchor event listener pattern).

JS Client Library

Source: https://docs.arcium.com/developers/js-client-library.md

• @arcium-hq/client is for encryption + submitting computations + tracking callbacks.
• @arcium-hq/reader is for observing the network/state.

Encrypting Inputs (Client)

Source: https://docs.arcium.com/developers/js-client-library/encryption.md

• Obtain MXE x25519 public key (getMXEPublicKey / retry helper).
• Generate ephemeral client keypair (x25519.utils.randomSecretKey, x25519.getPublicKey).
• Compute shared secret with MXE public key.
• Initialize RescueCipher(sharedSecret).
• Encrypt plaintext BigInts with 16-byte nonce; ciphertext outputs are [u8; 32] field elements.

Encryption (Concept)

Source: https://docs.arcium.com/developers/encryption.md

• Encrypted data is represented as Enc<Owner, T>.
• Owners:
  • Shared: client + MXE can decrypt (shared secret)
  • Mxe: MXE-only
• Internally: x25519 key exchange + Rescue cipher in CTR mode.
• Nonce handling: MXE increments nonce by 1 for outputs; new nonce required for subsequent interactions.

Sealing (Re-encryption)

Source: https://docs.arcium.com/developers/encryption/sealing.md

• Arcium can re-encrypt results to a specific recipient public key ("sealing").
• Useful to share derived results without revealing underlying data.

Computation Lifecycle

Source: https://docs.arcium.com/developers/computation-lifecycle.md

• Actors: Client, MXE Program, Arcium Program, MPC Cluster.
• Flow: client encrypts -> MXE queues via CPI -> cluster processes -> Arcium verifies -> MXE callback runs.

Program Integration (Queue + Callback)

Source: https://docs.arcium.com/developers/program.md

• Queue instruction builds parameters via ArgBuilder.
• Callback instruction must be defined with #[arcium_callback(encrypted_ix = "...")].
• Callback function signature must be ctx: Context<...>, output: SignedComputationOutputs<T>.
• Use output.verify_output(&cluster_account, &computation_account).

Callback Accounts (Persisting Results)

Source: https://docs.arcium.com/developers/program/callback-accs.md

• If you want to store results, pass custom accounts into callback_ix(..., extra_accs).
• Recommended approach is to use the generated callback_ix() helper and pass &[CallbackAccount { pubkey, is_writable }].
• Accounts must exist before callback executes; cannot create accounts during callback.
• Account ordering matters: 6 standard accounts first, then custom accounts.

Computation Definitions

Source: https://docs.arcium.com/developers/program/computation-def-accs.md

• Each encrypted instruction has a computation definition account.
• comp_def_offset computed from sha256(name)[0..4] as little-endian u32.
• For large circuits, use offchain circuit storage (CircuitSource::OffChain) with a URL and circuit_hash!().

Callback Type Generation

Source: https://docs.arcium.com/developers/program/callback-type-generation.md

• Output types are auto-generated from circuit return types.
• Expect PascalCaseInstructionName + Output and numbered fields (field_0, ...).
• Encryption wrappers become SharedEncryptedStruct<N> / MXEEncryptedStruct<N>.

Arcis: Input/Output

Source: https://docs.arcium.com/developers/arcis/input-output.md

• Use to_arcis() to convert encrypted input into secret-shared values.
• Use owner.from_arcis(...) to output encrypted values.
• Avoid plaintext parameters for sensitive data (ARX nodes can see them).
• For large arrays, consider Pack<T> and generated packers.

Arcis: Mental Model

Source: https://docs.arcium.com/developers/arcis/mental-model.md

• Circuits are fixed at compile time.
• If conditions on secret/shared values: both branches execute; condition selects result.
• Loops must have compile-time bounds; no while, break, continue.
• reveal() / from_arcis() cannot be inside non-constant branches.

Current Limitations

Source: https://docs.arcium.com/developers/limitations.md

• Output size must fit into one callback transaction; practical limit ~1232 bytes.