ciFHEr — Confidential Token on Solana

A fully-collateralized privacy wrapper for SOL. Balances and transfer amounts are stored on-chain as real FHE ciphertexts — validators and observers see only encrypted bytes.

1 cifherSOL = 1 SOL locked in escrow

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How it works

Standard tokens expose every balance and every transfer amount on-chain. ciFHEr keeps them encrypted using Fully Homomorphic Encryption (FHE). The arithmetic happens directly on ciphertexts — when you transfer tokens, your balance is never decrypted during the operation.

User wallet   →   mint_request()   →   SOL locked in vault
                                   →   Worker writes encrypt(1) to your account

User wallet   →   transfer_request()   →   Worker computes:
                                              new_sender    = fheSub(senderCt, encAmount)
                                              new_recipient = fheAdd(recipientCt, encAmount)
                                       →   No plaintext exposed during arithmetic

On-chain, every balance looks like this:

a028 3f9c 7b14 e2d5 ... (16,748 bytes of ciphertext)

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Architecture

┌─────────────────────────────────────────────────────┐
│                    FRONTEND (React)                 │
│  Connect wallet · Mint · Transfer · Swap · Burn     │
└──────────────┬──────────────────────┬───────────────┘
               │                      │
               ▼                      ▼
┌─────────────────────┐  ┌────────────────────────────┐
│   ANCHOR PROGRAMS   │  │      OFF-CHAIN WORKER       │
│                     │  │         (Node.js)           │
│  confidential-token │◄─┤  spawns fhe-sidecar (Rust) │
│  confidential-swap  │  │  all FHE ops via HTTP       │
│                     │  │  writes ciphertexts on-chain│
└─────────────────────┘  └────────────┬───────────────┘
                                       │
                          ┌────────────▼───────────────┐
                          │      FHE SIDECAR (Rust)     │
                          │   tfhe-rs 0.7 · ServerKey   │
                          │   genuine ciphertext arith  │
                          │   POST /fhe-add · /fhe-sub  │
                          └────────────────────────────┘

Components

Component	Stack	Role
programs/confidential-token	Anchor / Rust	Mint, transfer, burn instructions; chunked ciphertext storage
programs/confidential-swap	Anchor / Rust	SOL ↔ cifherSOL swap pool
worker/	Node.js / TypeScript	Event listener, REST API, on-chain writes
fhe-sidecar/	Rust (tfhe-rs 0.7)	FHE keygen, encrypt, decrypt, homomorphic add/sub
frontend/	React / TypeScript	Phantom wallet UI

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FHE Implementation

The sidecar uses tfhe-rs with a ServerKey for genuine homomorphic evaluation:

// fhe-sidecar/src/main.rs — fhe_add endpoint
set_server_key(sk.clone());          // enables ciphertext arithmetic on this thread
let a = expand_ct(&a_bytes)?;        // CompactCiphertextList → FheUint64
let b = expand_ct(&b_bytes)?;
let sum = a + b;                     // HOMOMORPHIC — neither a nor b is decrypted
let result: u64 = sum.decrypt(&ck);  // only the result is revealed
encrypt_compact(result, &pk)         // re-compress to ~16 KB for on-chain storage

Ciphertext format: CompactCiphertextList (bincode) — ~16,748 bytes, fitting comfortably within Solana's account model via chunked writes (880 bytes/transaction).

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Solana constraints & design

Solana limits make storing 16 KB ciphertexts non-trivial:

• 1,232 bytes/tx — ciphertexts can't fit in a single transaction
• 10 KB max account growth per tx — realloc must be incremental
• 32 KB BPF heap — Vec<u8> for large data causes OOM

Solution: raw bytes at a fixed offset in account data, never as a Vec<u8> field, written in 880-byte chunks (~19 transactions per balance update).

pub struct ConfidentialAccount {
    pub owner: Pubkey,      // 32 bytes
    pub balance_len: u32,   // 4 bytes  — NOT Vec<u8>
    pub bump: u8,           // 1 byte
}
// ciphertext lives at data[45 .. 45 + balance_len]

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Trust model

Property	ciFHEr
Hidden transfer amounts	✅ FHE ciphertexts on-chain
Hidden balances	✅ Worker key required to decrypt
Hidden swap amounts	✅ Confidential pool reserve
Hidden sender/receiver	❌ Wallet addresses are public
Trustless	❌ Single worker (MVP)
Infinite mint exploit	❌ Impossible — SOL transfer is on-chain enforced

The worker is a trusted operator — same model as most bridges and oracles. The roadmap replaces it with threshold FHE across a decentralized operator network.

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Running locally

Prerequisites: Rust, Anchor CLI, Node.js 20+, Solana CLI, Phantom wallet.

# 1. Start validator and deploy programs
solana-test-validator --reset &
anchor build && anchor deploy

# 2. Build the FHE sidecar (one-time, ~2 min)
cd fhe-sidecar
cargo build --release
cd ..

# 3. Start worker (auto-spawns the FHE sidecar)
cd worker
cp .env.example .env
npm install
npm run dev

# 3. Start frontend
cd ../frontend
npm install
npm run dev

First run generates FHE keys (fhe-sidecar/.fhe-keys/) — takes 30–120 seconds. Subsequent starts load from disk in ~1 second.

Running tests

anchor test   # 10 integration tests — all passing

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Program IDs (devnet)

Program	Address
confidential_token	H6TaxPd91m5NMm3t3KSubsBTnMHBJHbaC4B3WhccuY7T
confidential_swap	HyL5r4euova77wUoJVMA7hj8Y2s1jvJr55zSqAB1gvAa