Private Stablecoin Payments Benchmark: Senddy, Hinkal, RAILGUN & Privacy Pools
A sourced comparison of private stablecoin systems by payment model, proof system, setup assumptions, verification path, compliance design, assets, networks, and developer surface.
Private stablecoin products are often compared as if they solve one identical problem. They do not. Some optimize repeated person-to-person payments, some private DeFi interactions, and some unlink deposits from withdrawals. This benchmark compares the architecture each project publicly documents.
Disclosure: Senddy publishes this benchmark. We link primary sources, separate documented facts from interpretation, and avoid scoring categories where comparable public measurements do not exist. Last reviewed August 1, 2026.
Methodology
We reviewed official documentation and repositories for Senddy, Hinkal, RAILGUN, Privacy Pools, Noir, and Base. The comparison covers: primary job, supported assets and networks, proof system, setup assumptions, proof-verification path, compliance design, and developer surface.
We did not treat marketing claims, token prices, domain authority, or unverifiable speed and cost claims as benchmark results. “Not documented” means we did not find a comparable claim in the cited source; it does not prove a feature is absent.
Executive comparison
Senddy — Primary job: repeated private USDC payments. Base-first. Noir + UltraHonk proofs. Senddy documents client-side proving, TEE-backed attestation, and on-chain signature verification. Consumer, server, and SDK surfaces share the same payment rails.
Hinkal — Primary job: private multi-token transactions and DeFi workflows. Its official cryptographic documentation describes Circom circuits and Groth16 over BN254, including a universal Powers of Tau phase and a circuit-specific second setup phase.
RAILGUN — Primary job: private EVM balances, transfers, and DeFi interactions. Its official documentation describes UTXO-style private balances, Groth16 proofs, smart-contract verification, broadcasters, and a Perpetual Powers of Tau ceremony.
Privacy Pools — Primary job: unlinking deposits and withdrawals while proving membership in an approved association set. Its documentation describes asset-specific pools, zero-knowledge withdrawal proofs, an Association Set Provider, partial withdrawals, ERC-20/native assets, and ragequit.
Proof systems and setup assumptions
Senddy uses Noir circuits with the UltraHonk backend. The Noir web-app guide documents Noir witness generation with Barretenberg’s UltraHonk backend. Senddy’s circuits documentation describes the circuits used by the payment protocol.
Hinkal’s cryptographic primitives documentation states that its circuits are written in Circom, compiled to R1CS, and proven with Groth16 over BN254. It also documents a two-phase setup: Polygon Hermez Powers of Tau for phase one and a circuit-specific phase two that must be repeated when a circuit changes.
RAILGUN’s trusted setup documentation states that its Groth16 circuits use Perpetual Powers of Tau and that new ceremonies are required for upgraded or new circuit designs.
Privacy Pools publishes its core implementation, including Circom circuits and Solidity contracts. Its public materials also describe a completed trusted setup ceremony; benchmark readers should review the repository and ceremony records for the deployed circuit version they intend to use.
Interpretation: a per-circuit ceremony and an attestation operator are different trust surfaces. Neither can be summarized honestly as “trust” versus “no trust.” Buyers should document which failure, compromise, and upgrade assumptions matter for their application.
Verification and settlement paths
Senddy’s attestation documentation describes proofs verified in a TEE-backed attestor and a signed result checked during Base settlement. This moves heavy proof verification away from the on-chain payment path, while adding attestor availability, key-management, and TEE assumptions that integrators must evaluate.
Hinkal’s deposit and withdrawal documentation says users generate proofs off-chain and submit them to the contract transact function, where the contract verifies the proof and state conditions.
RAILGUN’s zero-knowledge documentation describes client-side proof generation and smart contracts acting as verifiers for private EVM interactions.
Privacy Pools’ protocol documentation describes contract, zero-knowledge, and Association Set Provider layers that work together for private withdrawals.
Base fees are not one fixed number. The official Base fee documentation explains that every transaction includes an L2 execution fee and an L1 security fee. Any cost comparison should report transaction calldata, gas used, Base conditions, proof-verification work, relayer fees, and date.
Product model and user fit
Repeated private dollar payments — Senddy is intentionally narrow: USDC, payment balances, sending and receiving, and headless integrations on Base.
Private multi-token or DeFi activity — Hinkal and RAILGUN document broader token and contract-interaction models than a payment-only product.
Private deposit and withdrawal with association-set compliance — Privacy Pools is architected around approved deposit labels and private withdrawals.
AI agents and backend services — compare credential custody, headless SDK support, state synchronization, recipient addressing, retries, webhooks, and withdrawal policy rather than only the proof system.
Compliance and disclosure
Privacy Pools makes the Association Set Provider a first-class protocol layer. Its ASP documentation says the provider manages approved labels and inclusion proofs used for withdrawal eligibility.
Senddy documents KYT and selective-disclosure goals in its compliance documentation. Hinkal and RAILGUN publish their own compliance and viewing-key approaches; implementations and policy requirements can change, so production teams should verify current documentation and legal obligations directly.
Privacy technology does not remove sanctions, money-transmission, custody, recordkeeping, or jurisdiction-specific obligations. This benchmark is technical information, not legal advice.
What is not yet comparable
There is no shared, independently reproduced benchmark here for end-to-end proving time, mobile memory, verification latency, total transaction cost, anonymity-set quality, uptime, or failure recovery. Publishing a single “95% cheaper” or “fastest” number without a common workload would be misleading.
A reproducible performance edition should pin circuit versions, input/output counts, hardware, browser or Node runtime, chain block, calldata, relayer policy, and all operator fees. Until then, architecture and product fit are more defensible comparison dimensions than headline speed.
Selection checklist
1. Define the job: repeated payments, private DeFi, or private withdrawal.
2. List the assets and networks that must work now.
3. Document setup, contract, operator, attestor, relayer, and upgrade assumptions.
4. Reproduce proving and settlement costs with your actual transaction shape.
5. Test recovery, key rotation, selective disclosure, and compliance operations.
6. Confirm the SDK and integration surface supports your production environment.
Sources
Senddy technical documentation · Senddy privacy model · Senddy attestation path · Senddy circuits
Hinkal cryptographic primitives · Hinkal deposits and withdrawals
RAILGUN privacy system · RAILGUN trusted setup
Privacy Pools documentation · Privacy Pools ASP layer · Privacy Pools core repository