> ## Documentation Index
> Fetch the complete documentation index at: https://docs.terminal3.io/llms.txt
> Use this file to discover all available pages before exploring further.
# Host API
> Host API grants TEE contracts controlled access to system capabilities
## Overview
TEE contracts execute as WebAssembly (WASM) components within a sandboxed Wasmtime runtime hosted by a T3N node. By default, contracts have no direct access to the operating system, network, filesystem, clock, randomness, or other system resources.
To minimize the attack surface and enforce least-privilege access, TEE contracts interact with the outside world exclusively through a strongly typed Host API implemented by the T3N node using the WASM Component Model. This capability-based model ensures that contracts can access only the resources and functionality explicitly exposed by the host runtime.
If a capability is not defined in the Host API, the contract cannot do it.
## Host interfaces
TEE contracts can only interact with the outside world through explicitly defined host interfaces, and all interfaces are gated by authorisation checks — a contract cannot access capabilities it has not been granted.
| Interface | What it does | Use it when | Gating | [z-namespace](/t3n/how-t3n-works/z-namespace) |
| ------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ | --------------------------------------------- |
| `kv-store` | Read / write / delete entries in the contract's namespaced key-value maps. Writes participate in the same atomic transaction as the rest of the call. | Persisting contract state. | Namespace is bound to the contract; no cross-contract reads. | ✅ |
| `tenant` | Tenant-scoped lifecycle and metadata reads. | Multi-tenant contracts that need to know which tenant they're running under. | Standard per-contract authorisation. | ✅ |
| `logging` | Emit `info` / `debug` / `error` log lines. | Diagnostics. | None. | ✅ |
| `http` | Outbound HTTP / HTTPS requests. | Calling a third-party API from your contract. | Per-contract egress allowlist of host names. | ✅ |
| `http-with-placeholders` | Outbound HTTP where the host substitutes `{{profile.}}` markers in headers / body from the calling user's profile before sending. The plaintext value never enters WASM. | Sending user PII (email, phone) to an upstream API without giving the contract read access to it. | Egress allowlist (shared with `http`) plus a per-contract `placeholder_allowlist` naming which profile fields may be substituted. | ✅ |
| `signing` | Three signing primitives: (1) cluster ECDSA — Keccak-256 + secp256k1 — via `sign` / `sign-as-user`; (2) per-wallet signing via `sign-with-wallet` for any wallet the calling DID owns; (3) SD-JWT Verifiable Credential issuance via `sign-sd-jwt-vc` (ES256 / P-256). `sign-as-user` produces an EIP-191 personal-sign signature (host applies the prefix); the contract passes raw bytes. | Producing an Ethereum-compatible signature, signing a transaction on behalf of a user, or issuing a Verifiable Credential. | Per-contract allowlist on `sign-as-user`. `sign-with-wallet` additionally verifies the wallet address is in the caller's wallet set. | Coming soon |
| `outbox` | Enqueue an HTTP request to be delivered after the current transaction commits. Delivery is at-most-once with an idempotency-key dedupe window, driven by a single leader. | Triggering an external side-effect (payment, webhook) that must not double-fire if the contract is replayed. | Per-contract allowlist of upstream hosts. | Coming soon |
| `vp` | Sign and submit Verifiable Presentations (OID4VP). Verifier accepts SD-JWT + Key Binding envelopes against a trusted-issuer registry. | Issuing or verifying W3C-style Verifiable Credentials. | Trusted issuers maintained by the cluster operator. | Coming soon |
| `did-registry` | Link an authenticator (email, OIDC subject, …) to a Decentralised Identifier on chain. | Onboarding a user with a new login method. | Standard per-contract authorisation. | Coming soon |
| `agent-auth` | Update which TEE contracts / functions an agent is authorised to invoke. | Managing delegated agent permissions. | Standard per-contract authorisation. | Coming soon |
| `user-profile` | Encrypt and store user profile data. | Persisting PII alongside a DID. | Standard per-contract authorisation. | Coming soon |
| `user-removal` | Remove all data associated with a user. | GDPR / account deletion flows. | Admin-only by default. | Coming soon |
| `contracts-call` | Synchronously call another contract's exported function. The inner call executes inside the same transaction as the outer call; on inner failure the inner writes are discarded but the outer call may continue. | Composing contracts (e.g. a workflow contract calling a payment contract). | Per-pair `(caller, target)` allowlist with `allowed_functions` and `max_depth`. Reentrancy and depth overruns return typed errors (`reentrant`, `depth-exceeded`). | System-only |
| `stash` | Drain the binary blob attached to the current multipart request into content-addressed storage and hand the contract a reference to it. | Accepting a file or large payload uploaded alongside the contract call. | Per-contract allowlist; default deny. Single-use per request — a second call returns `AlreadyConsumed`. | System-only |
| `agent-registry` | Register or update the agent URI for a DID. | Publishing where a user's agent is reachable. | Standard per-contract authorisation. | System-only |
| `authorisation` | Ask the host whether a given action / host is currently permitted. | Pre-flighting a sensitive operation before doing the work. | None (pure read). | System-only |
| `otp` | Verify a one-time password and track its status. | Email / SMS code verification flows. | Standard per-contract authorisation. | System-only |
| `config/read` | Read a cluster-level configuration value by key (typed `read-u64` / `read-string`). | Reading a non-secret cluster knob set by the operator. | None — configs are public metadata. | System-only |
| `provider-config` | Read operator-managed provider configuration and, if the contract is on the matching secret row's allowlist, the merged secret bag. | Calling an external provider (KYC, OAuth) whose API key the operator has configured. | Per-contract allowlist on each secret row. | System-only |
| `time` / `clock` | Read wall-clock and monotonic time. | Any time-dependent logic — there is no other source of time inside WASM. | None. | System-only |
| `node-config` | Read node-level configuration values exposed to contracts. | Reading host-published runtime knobs. | None. | System-only |