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A complete reference implementation demonstrating how to build a privacy-preserving orderbook on Solana using Privora’s FHE capabilities.

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Why Privacy Matters in Trading

Traditional orderbooks expose sensitive information:
Exposed DataPrivacy Risk
Order pricesFront-running attacks
Order quantitiesPosition size exposure
Trade historyTrading strategy leakage
With FHE, orders are matched without revealing prices or quantities to anyone - not even the validators processing transactions.

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Architecture Overview

┌─────────────┐    Submit Order     ┌────────────────┐
│   Trader    │ ──────────────────→ │   Orderbook    │
│  (Client)   │                     │   (Program)    │
└─────────────┘                     └────────────────┘
      │                                     │
      │ Encrypt                             │ Match
      ▼                                     ▼
┌─────────────┐                     ┌────────────────┐
│ FHE Public  │                     │ FHE Operations │
│    Key      │                     │ (Encrypted)    │
└─────────────┘                     └────────────────┘
                                            │
                                            ▼
                                    ┌────────────────┐
                                    │ Match Result   │
                                    │ (Encrypted)    │
                                    └────────────────┘

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Key Features

Encrypted Orders

Prices and quantities are encrypted client-side before submission

Private Matching

Orders matched using FHE comparisons - no plaintext exposure

Minimal Storage

Only 32-byte hash references stored on-chain

Authorization Control

PDAs control who can decrypt match results

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Data Flow

1

Encrypt Order

Client encrypts price and quantity using FHE public key
2

Submit to Store

Encrypted data submitted to content-addressable store, receives hash
3

Create Order

Order account created with EncryptedRef hashes (32 bytes each)
4

Match Orders

Program loads encrypted data, performs FHE comparison and min
5

Store Result

Fill price and quantity stored, authorization PDAs created
6

Decrypt

Authorized users can request decryption of their fill details

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Program Structure

fhe_orderbook/
├── src/
│   ├── lib.rs           # Entry point, instruction enum
│   ├── state.rs         # Order, Orderbook, MatchResult structs
│   └── instructions.rs  # Handler functions
└── tests/
    └── orderbook_test.rs # Integration tests

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Account Sizes

The orderbook uses minimal account space by storing only hash references:
AccountSizeContents
Order106 bytesowner, price_ref, qty_ref, side, status, order_id
Orderbook56 bytesauthority, next_order_id, counters
MatchResult88 bytesorder IDs, fill_price_ref, fill_qty_ref, match_id
Compare to storing raw ciphertexts (~4KB each), this is a 40x reduction.

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Instructions

InstructionDescription
InitializeCreate orderbook with authority
SubmitOrderSubmit buy/sell order with encrypted price and quantity
MatchOrdersMatch a buy and sell order using FHE
CancelOrderCancel an open order (owner only)

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Next Steps

State Structures

Learn about Order, Orderbook, and MatchResult

Instructions

See instruction implementations

Matching Logic

Understand FHE comparison and min

Client Usage

Integrate with frontend