> For the complete documentation index, see [llms.txt](https://docs.useprivatus.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.useprivatus.com/protocol-and-architecture/protocol-overview.md).

# Protocol Overview

Privatus is the private financial layer of the agent economy, built on Solana with Token-2022 confidential balances, the confidential transfer extension native to Solana's token program, as its privacy primitive. Solana is the only major L1 with encrypted amounts built into the protocol itself, and Privatus builds directly on that foundation with its own Rust programs, written with Anchor, for handles, agent accounts, spend policies, and disclosure. And unlike a typical fintech product, Privatus doesn't run its own settlement ledger. Settlement is Solana mainnet itself.

***

## What the protocol layer does

1. **Custody and signing:** every account is a PDA-based smart account controlled by a keypair generated client-side, with Squads multisig for recovery and key rotation. Privatus never holds keys.
2. **Confidential transfers:** transfer amounts are stored as twisted ElGamal ciphertexts under Token-2022 confidential balances, with proof generation happening on the client and verification by Solana's native ZK proof program.
3. **Shielded state:** a commitment-tree shielded pool commits account state as Merkle roots on-chain, proven with Groth16 and verified through Solana's alt\_bn128 syscalls, with stealth meta-addresses for unlinkable receiving.
4. **Fee abstraction:** a small SOL reserve is maintained per account automatically and topped up via an internal swap when it drops below threshold, so users only ever think in USDG. Network fees, a fraction of a cent per transaction, become an implementation detail.
5. **Agent policy enforcement:** spend policies are checked client-side in the agent's signing flow, and enforced on-chain by the Privatus agent program.
6. **Indexing:** on-chain events are indexed off-chain via program log streams, powering the real-time feed and webhook system without requiring any party to poll the chain directly.

Everything that requires trust, meaning custody of funds and the validity of a transfer, is enforced by Solana consensus and Privatus's on-chain programs. Everything else, UI rendering, notifications, indexing, is a convenience layer riding on top. That separation is the architecture.

***

## Stack

```
+-----------------------------------------------+
|              Privatus App Layer               |
|      Web app . Mobile (iOS/Android) . SDK      |
+---------------------+---------------------------+
                       |
+---------------------v---------------------------+
|              Privatus API Layer                |
|   REST + WebSocket . Agent API . Webhooks       |
+---------------------+---------------------------+
                       |
+---------------------v---------------------------+
|            Privatus Core Services              |
|                                                 |
|  Wallet Engine   Privacy Engine   Agent Engine  |
|  (key mgmt,      (ZK proof gen,   (spend        |
|   tx building)    client-side)    policies,     |
|                                    x402 handler) |
|                                                 |
|  Indexer (program event streams + PostgreSQL)   |
+---------------------+---------------------------+
                       |
+---------------------v---------------------------+
|               Solana Mainnet                    |
|  Token-2022 Confidential Balances . ZK Proof    |
|  Program . Shielded Pool . Agent Program . x402 |
+-----------------------------------------------+
```

***

## Trust model

* **Users** don't need to trust Privatus with their funds. Keys are generated and held on-device; Privatus's servers see signed transactions, never private keys.
* **Users** don't need to trust Privatus with their transaction amounts. Proof generation and decryption happen client-side. Privatus's backend only ever handles ciphertext, and so does the network: Solana's globally distributed validator set orders ciphertexts without ever seeing balances or transfer values.
* **Agents** operate under spend policies enforced at the signing layer and in the on-chain agent program, not by Privatus's discretion after the fact. A transaction that violates policy is never produced in the first place.

***

## Further reading

* [On-Chain Architecture](/protocol-and-architecture/on-chain-architecture.md): the program and account state layout underneath Privatus
* [Trust & Security Model](/protocol-and-architecture/trust-and-security.md): the full security layer breakdown


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