arcium

# Arcium Encrypted computation on Solana via MPC. Data stays encrypted during computation. The `arcium` CLI (wraps Anchor) handles init, build, test, and deploy — use MCP for current flags and options. **MCP Tools**: `search_arcium_docs` for discovery (returns page path), then `query_docs_filesystem_arcium_docs` with `cat <path>.mdx` for full-page reads (e.g., `cat /developers/arcis/mental-model.mdx`). ## When to Use **Use when:** - You need trustless computation -- cryptographically guaranteed, no single party sees the data - Multiple parties compute on combined data without revealing inputs - On-chain state must remain encrypted but computable - Privacy: sealed-bid auctions, voting, hidden game state, dark pools, confidential DeFi **Constraints:** - Fixed loop bounds required (no variable-length iteration) ## Mental Model Arcium apps have three coupled surfaces. Most bugs are mismatches across their boundaries: | Surface | Responsibility | Common Boundary Bugs | |---------|---------------|----------------------| | **Circuit** (Arcis/Rust) | Pure fixed-shape MPC logic | Variable loops, dynamic collections, `.reveal()` inside conditionals | | **Program** (Anchor/Rust) | Orchestration: init + queue + callback | Macro name mismatch, callback accounts not writable, wrong ArgBuilder order | | **Client** (TypeScript) | Key exchange, encryption, submission, decryption | Nonce reuse, missing `.x25519_pubkey()` for Shared, param order ≠ circuit order | **MPC constraints** (f...