Agent DNSTT Rendezvous

Authorization-gated coordination skill for agents that need to plan, verify, and troubleshoot a DNSTT client/server link without sharing private keys, scanning resolvers, changing DNS/firewalls, or auto-executing tunnel commands. Uses short-lived rendezvous cards, out-of-band public-key fingerprints, optional HMAC authentication, loopback-by-default services, deterministic argv plans, and secret-free status handoffs. Use only on domains, resolvers, servers, and services the operator owns or is explicitly authorized to administer.

A distinct, original agent-coordination layer for authorized DNSTT links. It does not implement DNSTT, copy another project's code, download binaries, scan the public Internet, change DNS/firewalls, or start processes. It helps a server agent, client agent, and optional observer agent agree on the same short-lived connection facts and produce commands for a human to review.

When to use

Use this skill when all of the following are true:

1. The operator owns or has written authorization for the tunnel domain, server, resolver, and upstream service.
2. A compatible dnstt-server and dnstt-client are already obtained from a trusted source and verified separately.
3. Agents need a safe handoff: domain, server public key, fingerprint, listener, loopback upstream, expiry, purpose, and authorization reference.
4. A human will review and execute any generated command.

Do not use it for covert access, policy evasion, unauthorized proxying, data exfiltration, public-resolver sweeps, open proxies, or hiding activity from network owners. DNSTT traffic is observable in DNS logs and is not an anonymity system.

Distinct design

This skill is a coordination protocol rather than a tunnel implementation:

• Short-lived rendezvous cards expire automatically.
• Out-of-band key pinning is mandatory for client plans.
• Optional HMAC authentication protects agent-to-agent card handoff.
• No private key ever enters a card or client plan.
• Loopback by default: server upstream and client listener are local-only.
• No automatic execution: commands are emitted as JSON argv arrays.
• No network scanning: only an operator-supplied resolver may be planned.
• Secret-free status reports let agents help each other diagnose which side is failing without exchanging credentials.

Roles and cooperation protocol

🖥️ Server agent

1. Confirms written authorization and the intended single TCP service.
2. Generates a DNSTT keypair locally using a reviewed plan.
3. Keeps the private key mode 0600; shares only the public key.
4. Creates a rendezvous card with an expiry and authorization reference.
5. Sends the card and public-key fingerprint through separate channels.
6. Produces a server command plan but never executes it automatically.

💻 Client agent

1. Receives the card and independently receives the public-key fingerprint.
2. Verifies card integrity, expiry, fingerprint, and optional HMAC.
3. Uses only the operator-approved UDP, DoH, or DoT resolver.
4. Keeps its local DNSTT listener on loopback unless LAN access was explicitly approved.
5. Produces a client plan and public-key-file handoff for human review.

👁️ Observer/helper agent

1. Compares client/server status reports by card_id.
2. Confirms timestamps and state transitions.
3. Runs only the bounded diagnostic checklist—never broad scans.
4. Helps classify a failure as delegation, key pinning, DNS path, listener, upstream service, or intermittent transport.

State machine

planned → authorized → configured → reachable → connected → verified → closed

Failures use the failed state with a secret-free observation. Agents do not advance state based on claims alone; each transition needs observable evidence.

Installation

The skill helper uses Python's standard library only:

bash

python3 scripts/rendezvous.py --help
python3 -m unittest discover -s tests -v

DNSTT binaries are optional external runtime dependencies for executing a reviewed plan. This skill never downloads them.

Debugging preflight

Run the read-only doctor and complete regression suite before any release or when diagnosing unexpected behavior:

bash

PYTHONDONTWRITEBYTECODE=1 python3 scripts/rendezvous.py doctor
PYTHONDONTWRITEBYTECODE=1 python3 -m unittest discover -s tests -v

For structured, secret-free diagnostics, put global flags before the subcommand:

bash

python3 scripts/rendezvous.py --debug --json-errors verify-card \
  --card ./state/rendezvous-card.json \
  --expected-fingerprint 'sha256:<64-lowercase-hex>' \
  --hmac-env AGENT_LINK_SECRET \
  --require-hmac

See DEBUGGING.md for the bug matrix, error codes, reproduction protocol, property/fuzz/concurrency testing, and future-fix acceptance criteria.

Authorized lab workflow

The examples use reserved documentation names and addresses. Replace them only with infrastructure you are authorized to operate.

1. Server: request a key-generation plan

bash

python3 scripts/rendezvous.py keygen-plan \
  --privkey-file ./state/server.key \
  --pubkey-file ./state/server.pub \
  --ack-authorized \
  --output ./state/keygen-plan.json

Review command_argv, run it manually, then protect the private key:

bash

chmod 600 ./state/server.key

2. Server: create a short-lived card

bash

export AGENT_LINK_SECRET='replace-with-a-strong-shared-coordination-secret'
python3 scripts/rendezvous.py server-card \
  --agent-id server-agent-a \
  --domain t.example.com \
  --pubkey-file ./state/server.pub \
  --listen 0.0.0.0:5300 \
  --upstream 127.0.0.1:8000 \
  --expires-minutes 30 \
  --authorization-ref LAB-2026-001 \
  --purpose 'authorized agent message service' \
  --hmac-env AGENT_LINK_SECRET \
  --ack-authorized \
  --output ./state/rendezvous-card.json

The card contains a public key, never a private key. Send the displayed sha256:<64hex> public-key fingerprint to the client through a separate, authenticated channel. Operational plans require an HMAC-authenticated card by default; --allow-unsigned-card is an explicit offline-workflow waiver, not a normal convenience flag.

3. Server: generate a reviewed server plan

bash

python3 scripts/rendezvous.py server-plan \
  --card ./state/rendezvous-card.json \
  --privkey-file ./state/server.key \
  --hmac-env AGENT_LINK_SECRET \
  --ack-authorized \
  --output ./state/server-plan.json

The helper refuses private key files with group/world permissions. It does not modify DNS, firewall rules, services, or systemd.

4. Client: verify the card

bash

python3 scripts/rendezvous.py verify-card \
  --card ./state/rendezvous-card.json \
  --expected-fingerprint 'sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef' \
  --hmac-env AGENT_LINK_SECRET

Use the real fingerprint received out of band. A mismatch is a hard stop.

5. Client: generate a reviewed client plan

bash

python3 scripts/rendezvous.py client-plan \
  --card ./state/rendezvous-card.json \
  --expected-fingerprint 'sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef' \
  --transport udp \
  --resolver 192.0.2.53:53 \
  --local-listen 127.0.0.1:7000 \
  --pubkey-file ./state/server.pub \
  --hmac-env AGENT_LINK_SECRET \
  --ack-authorized \
  --output ./state/client-plan.json

The output contains the public-key file content and a DNSTT client argv array. It writes neither file and starts no process.

6. Agents exchange authenticated status chains

Start with planned:

bash

python3 scripts/rendezvous.py status-report \
  --card ./state/rendezvous-card.json \
  --agent-id client-agent-b \
  --role client \
  --state planned \
  --message 'card verified; awaiting operator approval' \
  --expected-fingerprint 'sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef' \
  --hmac-env AGENT_LINK_SECRET \
  --require-hmac \
  --output ./state/client-planned.json

Each later state must provide the previous report. For example:

bash

python3 scripts/rendezvous.py status-report \
  --card ./state/rendezvous-card.json \
  --agent-id client-agent-b \
  --role client \
  --state authorized \
  --message 'operator approval recorded' \
  --previous-report ./state/client-planned.json \
  --expected-fingerprint 'sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef' \
  --hmac-env AGENT_LINK_SECRET \
  --require-hmac \
  --output ./state/client-authorized.json

Verify a chained report with its predecessor:

bash

python3 scripts/rendezvous.py verify-status \
  --card ./state/rendezvous-card.json \
  --status ./state/client-authorized.json \
  --previous-report ./state/client-planned.json \
  --expected-fingerprint 'sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef' \
  --hmac-env AGENT_LINK_SECRET \
  --require-hmac

Status messages containing token/password/private-key patterns or control characters are rejected. The HMAC tag authenticates the report but is not the secret itself.

Read-only diagnostics

bash

python3 scripts/rendezvous.py diagnose \
  --card ./state/rendezvous-card.json \
  --symptom no-response \
  --expected-fingerprint 'sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef' \
  --hmac-env AGENT_LINK_SECRET

Available symptoms:

• dns-delegation
• key-mismatch
• no-response
• connects-no-service
• intermittent

Diagnostics print bounded checks. They never probe hosts or resolver ranges.

DNSTT compatibility notes

DNSTT is a userspace TCP tunnel over delegated DNS, not a full VPN. A typical server forwards incoming streams to a single TCP endpoint, while a client opens a local TCP listener. Exact flags differ by build/fork; always compare the plan with the installed binary's --help before execution.

A tunnel DNS zone normally needs an NS delegation to a nameserver hostname with A/AAAA records for the authorized server. This skill does not create records. The server plan defaults to UDP port 5300 so DNSTT need not run as root; an operator may separately review port-53 forwarding. No firewall command is created here.

v1.1.0 debugging and hardening

A full adversarial audit reproduced and fixed twelve bug classes:

1. short HMAC secrets;
2. permissive card schemas/endpoints/constraints;
3. future-issued or overlong-lived cards;
4. duplicate/non-finite/oversized/over-complex JSON;
5. output symlink overwrite and partial-write risk;
6. DoH URLs containing credentials/query/fragment data;
7. private-key symlink and ownership/mode risks;
8. secret-bearing status messages marked safe;
9. unsigned operational cards accepted without an explicit waiver;
10. LAN listeners overriding a signed loopback-only card;
11. status reports skipping state transitions;
12. test-only dynamic imports triggering static security scans.

The fix set adds strict schemas, bounded no-follow reads, atomic mode-0600 writes, 32-byte HMAC minimum, safe binary/path parsing, dual-consent LAN listeners, authenticated status chains, structured error codes, secret-free debug events, a read-only doctor, and fail-closed CLI handling.

Verification now includes 31 unit/regression/property/fuzz/concurrency tests: 500 signed-card round trips, 2,000 endpoint fuzz cases, 1,000 malformed JSON cases, mutation checks, and 64 concurrent atomic writers.

Safety boundaries

• Never expose an unauthenticated general-purpose proxy.
• Keep the server upstream loopback-bound and application-authenticated.
• Keep client listeners loopback-bound unless LAN access is explicitly needed.
• Limit card lifetime, sessions, query rate, and upstream scope.
• Treat DNS resolvers and network operators as able to observe tunnel metadata.
• Never include private keys or coordination secrets in cards, logs, status reports, prompts, issue reports, or chat.
• Do not use a DNS tunnel where policy or law forbids it.
• Stop and close the session after the authorized task.

Originality and inspiration

No source code, UI, configuration format, profile URI, branding, assets, or text was copied from the referenced projects. Architectural lessons were studied at a high level: client/server role separation, resolver-aware health, explicit profiles, key pinning, bounded service management, and clear diagnostics. This skill's card schema, HMAC handoff, state machine, safety gates, planner, tests, and documentation are original.

See references/INSPIRATION.md for project links, license boundaries, and the specific ideas that were transformed rather than copied.