Portmark

A signed leash for AI agents that go out and act — enforced by the host, not the prompt.

Agents are starting to do things: spend, book, transact. Portmark makes that authority explicit and cryptographic. An agent travels as a signed envelope — its manifest, its permit (the exact scope it may act in), its state checkpoint, and its code identity. The host verifies the signature, intersects the requested authority with its own policy, and mediates every single tool call. A vague instruction or a prompt injection can't widen the permit, because the limit lives in the runtime, not the model — and the agent's model proposes actions but never executes them and never sees your credentials.

It works both ways, and either side is useful on its own:

• Send an agent with a permit it can't exceed — dispatch it and know a misread instruction or an injection can't make it overspend or overreach.
• Host agents you didn't write — run incoming agents mediated, capped by your policy, and audited, without trusting their behavior.

Built on A2A — Google's Agent2Agent protocol. Portmark's agent card is byte-identical to the official SDK's, so it drops into the A2A ecosystem you're already building in; the signed permit is the capability-security layer A2A leaves to you.

What the host is guaranteed

These are enforced by the host, not requested politely from the agent:

• Your policy is a hard ceiling. effective_permit intersects three sets: what the agent's manifest asks for, what its permit grants, and what your host policy allows. An agent arriving with a permit for * still gets only what you allow. (security.py, intersect_grants)
• Budgets take the minimum. Steps, tool calls, and output bytes are each min(agent, host). A visitor cannot raise its own limits. (models.py, ResourceBudget.intersect)
• Wasm capsules declaring any import are refused, not sandboxed. The guest therefore has no filesystem, network, process, environment, clock, randomness, or credential access at all. (wasm_runner.mjs) This bounds access, not consumption: on the default Node runner the guest can still grow its own linear memory unbounded and exhaust host RAM before the wall-clock deadline fires — the Node path caps time, not memory. Only the optional native Wasmtime engine bounds guest memory as well (store.set_limits(memory_size=…) alongside a fuel budget in wasmtime_component_runner.py). A deployment that must resist a memory-exhaustion capsule should select --wasm-engine wasmtime.
• Permits can only narrow on migration. One hop, bound to the named destination, grants and budgets cannot increase, and further delegation is disabled. A visiting agent cannot accept a narrow permit at your door and widen it on the next hop.
• Every run is auditable. A hash-chained audit log records the accepted agent, the active policy version and hash, each proposal, and each executed tool call.

Portmark runs entirely offline by default. The deterministic provider is for demonstrations and tests. GenericHttpProvider connects the same runtime to llama.cpp, Ollama through an adapter, a hosted model gateway, or anything implementing the small decision contract below.

Quickstart

git clone https://github.com/Itsthewayofyou/portmark.git
cd portmark
PYTHONPATH=src python -m portmark.cli demo "research modern mobile agents"

No installation and no network access required. Examples below use bash; on PowerShell, write $env:PYTHONPATH = "src" on its own line instead of the inline prefix.

Send an agent to a running host

Portmark has no user interface, because the client is another program rather than a person at a screen. Sending an agent takes three commands and no Python:

# 1. mint the agent's signing key and the public trust registry the host will load
portmark keygen --issuer user:alice --out-registry trust.json --format env > agent.env
chmod 600 agent.env

# 2. start a host that trusts that registry -- with no agent key in its environment
portmark --trust-registry-path trust.json serve --port 8080 &

# 3. load the agent key into your shell, build a signed request, and post it
source agent.env
portmark envelope --goal "find a red widget" --tool catalog.search > request.json
curl -X POST http://127.0.0.1:8080/message:send \
  -H 'Content-Type: application/json' --data @request.json

Steps 1 and 2 run once. Only step 3 repeats.

The agent key stays out of the host's environment on purpose. A host that inherits PORTMARK_SIGNING_ISSUER from a client would try to sign its own audit heads as the agent, so it refuses to start and says so.

portmark envelope prints a ready-to-POST message/send request by default, or the bare signed envelope with --format envelope. For anything past a single tool, pass a spec file:

portmark envelope --spec agent.json > request.json

{
  "agent_id": "agent:shopper",
  "goal": "find a red widget under $20",
  "audience": "host:local-demo",
  "ttl_seconds": 900,
  "grants": [
    {"name": "catalog.search", "constraints": {"max_limit": 3}, "output_projection": ["id", "title"]}
  ],
  "budget": {"max_steps": 6, "max_tool_calls": 2, "max_output_bytes": 32768}
}

Unknown fields are rejected rather than ignored, so a typo fails loudly instead of silently dropping a constraint. Three things are worth knowing before the first run:

• audience must equal the host's --host-id (default host:local-demo). A host will not run an envelope addressed to somebody else.
• Each envelope carries a fresh nonce. A saved request.json is single-use by design; re-posting it is a replay and the host refuses it. Rebuild it from the spec each time.
• Host policy is a ceiling, not a suggestion. A tool granted here that the host policy does not allow is dropped from the effective permit; the agent runs without it rather than failing.
• Constrain each argument in one place. When the envelope and the policy both constrain the same argument, the two are merged, and the merge only ever narrows — a combination Portmark cannot prove is narrower drops the grant instead of guessing. If a tool disappears, the host's error names the stage and the key responsible. The full table is in TOOLS.md.

The tools behind that boundary — catalog.search and payments.reserve — are deterministic stubs. The enforcement around them is real and tested; the things being enforced against are placeholders for your own. See TOOLS.md for installing a custom ToolRegistry with --tools module:function, granting it in host policy, and controlling provider-visible output.

Security boundary

A2A request / local CLI
        |
signed agent envelope
        v
Host verification -> permit intersection -> provider proposal
                                             |
                                 host validates every action
                                             v
                                  capability-scoped tools

The provider proposes actions but never receives host credentials and never authorizes its own tool calls. The host enforces subject, audience, expiry, replay nonce, tool grants, argument constraints, step budgets, tool-call budgets, output limits, and a hash-chained audit log.

Host policy can be loaded from JSON and every run records the active policy version and hash in the audit log. High-impact tools such as external payments, destructive actions, credentialed access, and data-exfiltration-risk actions require signed approval tokens bound to the task, permit nonce, tool arguments, and active policy hash. See POLICY.md for the policy format, reload behavior, approval-token contract, and audit events.

Migration requires delegation_allowed on the incoming permit. The source host can then create only a narrower, one-hop, destination-bound permit: the effective grants and budgets cannot increase, the audience changes to the named destination, the replay nonce is replaced, and further delegation is disabled. Both hosts must belong to the same configured trust domain in this reference implementation.

Hosts can require signed confidential-computing attestation evidence before sensitive execution or delegated migration. The reference verifier binds the attested host identity, relying-party audience, approved measurement, freshness window, optional nonce, and verifier signature before the host runs the agent or emits a migration envelope. Deployments can also configure a bounded, shell-free external verifier command for platform quotes. See ATTESTATION.md for the evidence format, verification flow, external-verifier contract, sealed-storage decision, and residual risks.

Envelopes are signed with Ed25519 by default and verified through a key-ID-based trust registry. See SIGNING_KEYS.md for key generation, rotation, revocation, trust bootstrap guidance, and why SPIFFE is a planned opt-in rather than the trust root. The legacy HMAC signer is retained only behind PORTMARK_ALLOW_LEGACY_HMAC=unsafe-test-only plus an explicit PORTMARK_SIGNING_KEY.

Run it

Install the project for normal package usage:

python -m pip install -e .
portmark demo "research modern mobile agents"

Execute the included Wasm capsule using the WIT-shaped resume(context-json, checkpoint-json) binding:

PYTHONPATH=src python -m portmark.cli --wasm-component capsules/research-agent.wasm.b64 demo "research modern mobile agents"

Deployments that install the optional native Wasmtime extra can select --wasm-engine wasmtime to instantiate the signed component bytes through wasmtime.component instead of the default Node runner:

python -m pip install -e '.[wasmtime]'
PYTHONPATH=src python -m portmark.cli \
  --wasm-component capsules/research-agent.component.wasm.b64 \
  --wasm-engine wasmtime \
  demo "research modern mobile agents"

The Node runner consumes capsules/research-agent.wasm.b64, which is a core Wasm module. Native Wasmtime consumes capsules/research-agent.component.wasm.b64, which is a Component Model artifact.

The host executes each capsule in a short-lived worker with a strict deadline and rejects every module declaring an import. Its signed SHA-256 digest is checked before execution. Tool actions returned by the capsule still pass through the same host permit and argument enforcement as model-provider proposals. See WASM_COMPONENTS.md for the WIT binding contract. The included example capsule performs a projected catalog.search step and then completes from checkpointed tool output.

Run tests:

PYTHONPATH=src python -m unittest discover -s tests -v

Run the A2A-facing HTTP service (served by uvicorn on loopback; front it with a reverse proxy for TLS):

PYTHONPATH=src python -m portmark.cli serve --port 8080

Require bearer authentication for A2A message submission:

PORTMARK_A2A_TOKEN=change-me PYTHONPATH=src python -m portmark.cli serve --port 8080

The reference A2A server is loopback-only for public deployments. Front it with a production HTTP proxy such as the Nginx example in deploy/nginx/portmark.conf. Public interface binds are refused; the legacy --allow-direct-a2a flag is accepted only for configuration compatibility and does not bypass the loopback requirement. The public Agent Card route is rate-limited separately from /message:send.

The Agent Card is available at /.well-known/agent-card.json; signed envelopes are submitted to /message:send with the A2A JSON-RPC message/send method. See A2A.md for the Agent Card fields, request shape, authentication profile, metrics endpoint, and error behavior.

To validate the Agent Card and request shape through the official SDK types, install portmark[a2a] and run serve --a2a-adapter sdk. The local adapter remains the default so base installs do not pull the SDK dependency tree.

Persist replay nonces, checkpoints, and signed audit heads with SQLite:

PYTHONPATH=src python -m portmark.cli --store-path runtime.sqlite demo "research modern mobile agents"

See RUNTIME_STORAGE.md for the storage schema, transaction guarantees, signed-head audit verification, and recovery behavior.

Load policy from JSON:

PYTHONPATH=src python -m portmark.cli --policy-path examples/host-policy.json --reload-policy demo "research modern mobile agents"

See OPERATIONS.md for runtime configuration, trust registry format, policy updates, audit verification, backup/restore, and incident response.

Generic provider contract

Start the CLI with --provider-endpoint URL. The runtime sends:

{
  "state": {
    "task_id": "...",
    "goal": "...",
    "step": 1,
    "tool_calls": 1,
    "status": "running",
    "messages": [
      {"role": "tool", "name": "catalog.search", "content": [{"id": "doc-1", "title": "..."}]}
    ]
  },
  "available_tools": ["catalog.search"]
}

state.messages contains only host-policy-projected tool output from prior steps. The host never sends raw checkpoint memory or result fields to remote providers. Configure per-tool sharing with output_projection in host policy; omit it or set [] to share no output, use top-level field names such as ["id", "title"] for dict outputs or lists of dicts, and use ["*"] only for tools whose full output may be sent to the provider.

The provider responds with one decision:

{"kind": "tool", "tool": "catalog.search", "arguments": {"query": "...", "limit": 3}}

or:

{"kind": "complete", "content": {"answer": "..."}}

MODEL_PROVIDER_TOKEN optionally supplies a bearer token. It is held by the host adapter, not included in the portable envelope.

WebAssembly component boundary

wit/portmark.wit defines the Wasm Component Model decision interface. The capsule exports a checkpoint-based resume operation that receives structured context and checkpoint JSON and returns a structured outcome. A compiled capsule therefore cannot directly acquire filesystem, network, process, database, or credential access; the host must explicitly validate and mediate every requested action.

The default runnable Node WebAssembly adapter uses the JSON-lowered WIT binding documented in WASM_COMPONENTS.md. An optional native Wasmtime provider can execute the signed Component Model artifact in a short-lived Python worker when portmark[wasmtime] is installed. Strong migration is implemented as checkpoint-and-resume: native stacks, threads, sockets, and file descriptors never cross hosts.

Production status

Portmark is reference-complete with six named substitution points. Signing and trust, transactional persistence, the A2A 1.0 surface, external policy with approval gates, WIT-shaped Wasm execution, and confidential-computing attestation are all implemented and covered by the regression suite. PRODUCTION_TASKS.md holds the task-level record.

It is a reference implementation: read it, fork it, and substitute the seams below. It is not intended as a drop-in production dependency.

Deployment integration points

Portmark is provider-neutral by design. The following are deliberate seams for the deploying environment to fill, not unfinished work. Each has a working reference implementation and a stable interface to substitute against.

License

MIT. See LICENSE.