> ## Documentation Index
> Fetch the complete documentation index at: https://trust-link-tsn.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# What TrustLink Labs Is Building: Protocols and Products

> Concrete artifacts from TrustLink Labs: TSN protocol, TIN registry, GPRU authorization, TCAP credit-only transitions, TrustLink Pay reference app, and TSN SDK.

TrustLink Labs builds open infrastructure for stablecoin payments. The current stack includes protocol programs, network services, a reference application, and SDKs. Everything is developed on Solana and designed to separate identity, authorization, settlement, and private balance accounting into independent layers.

## Concrete artifacts

### TSN protocol

The Transfer Settlement Network is the coordination layer for payments. It includes:

* Solana programs for intent acceptance, epoch treasury, and settlement enforcement.
* TSN Receiver for durable ingress, work storage, and short leases.
* TSN Node for stateless verification, route decisions, and permit signing.
* TSN RPC Gateway for controlled Solana RPC transport.

### TIN registry

The Transfer Identity Protocol issues and resolves 10-digit Transfer Identity Numbers. A TIN separates the identity a user shares from the wallet or protected receiving route used for settlement.

### GPRU authorization and routing

GPRU is a TSN-derived settlement identity for authorization and routing only. It is non-custodial: it never holds funds, balances, or custody keys. It is derived from a TIN privacy-receiving root, settlement commitment, epoch context, and authorization scope.

### TCAP

The Transfer Confidential Asset Protocol manages credit-only tip transitions and encrypted owner snapshots. TCAP stores commitments, sequence, policy, and nullifiers on chain. Private balance values remain in AES-GCM encrypted snapshots that the owner device decrypts locally.

### TrustLink Pay

TrustLink Pay is the reference application on top of TSN. It demonstrates native TIN-to-TIN payments, wallet-to-TIN routes, TIN-to-wallet public exits, and wallet-to-wallet compatibility flows. All routes use the same intent, verification, lease, commitment, and settlement boundaries.

### TSN SDK

The `@trustlink/tsn-sdk` package provides TypeScript interfaces for intent construction, route resolution, permit validation, and snapshot encryption.

<CardGroup cols={2}>
  <Card title="Architecture overview" icon="building" href="/overview/architecture">
    How TSN, TIN, GPRU, and TCAP fit together.
  </Card>

  <Card title="TCAP deep dive" icon="lock" href="/architecture/tcap">
    Credit-only transitions, commitments, and encrypted snapshots.
  </Card>

  <Card title="Developer quickstart" icon="code" href="/developers/getting-started">
    Build your first TSN payment intent.
  </Card>

  <Card title="TrustLink Pay" icon="external-link" href="https://trustlink-pay.vercel.app">
    Try the reference application.
  </Card>
</CardGroup>

## Scope statement

The following are separate milestones and are not presented as active production capabilities:

* Recurring payments and subscription-provider execution.
* Mainnet deployment.
* Formal cryptographic audits.
* Perfect unlinkability.
* Confidential debits and exits (these remain proof-gated and disabled).

## Related topics

* [About TrustLink Labs](/about/trustlink-labs)
* [Engineering principles](/about/engineering-principles)
* [Current technology](/about/current-technology)
* [Contribute](/about/contribute)