JDoor Assist

Consent-first, encrypted remote assistance for trusted local networks.

Official website · Source · Security policy

JDoor began as a 2022 school networking project co-created by Djenis Ejupi and NobodyToListen. Version 1.0.0 is a safety-focused modernization by Djenis: the unauthenticated “backdoor” prototype was replaced by an explicit remote-support product with a visible host, local approval, encrypted transport, bounded messages, and remote control disabled by default.

JDoor Assist is for authorized support only. It deliberately has no unattended access, persistence, remote shell, file transfer, webcam capture, privilege escalation, or stealth mode.

What works

• Direct screen sharing over TLS 1.2/1.3.
• Ephemeral ECDSA certificate for every host run, bound to the advertised host through a SAN.
• Certificate fingerprint embedded in the out-of-band pairing link.
• Client endpoint identification plus constant-time matching of the exact certificate fingerprint.
• Random 128-bit, single-use pairing token with a 10-minute lifetime.
• Local approval showing the viewer name, address, and verification code.
• View-only sessions by default; the host can enable or revoke input instantly.
• Bounded, versioned binary protocol with defensive parsing, pre-TLS per-address caps, and an absolute setup deadline.
• Session-scoped control permission and capture cleanup that cannot migrate to a later viewer.
• Daily local JSONL audit records without pairing secrets, capped at 5 MiB with 30-day retention.
• Modern Swing UI with HiDPI support and keyboard-accessible controls.

Run it

Prerequisites: JDK 21. The Maven Wrapper downloads the pinned Maven distribution.

./mvnw clean verify
java -jar target/jdoor-assist-1.0.0-all.jar

On Windows:

.\mvnw.cmd clean verify
java -jar target\jdoor-assist-1.0.0-all.jar

From the launcher:

1. The person receiving help chooses Share this screen.
2. They copy the one-time jdoor:// link through a trusted channel.
3. The helper chooses Join a session, pastes the link, and requests access.
4. Both devices show the verification code before approval; the host compares it and approves locally.
5. The session starts view-only. The host may enable mouse and keyboard control.
6. Either side can end the session; the host can revoke control at any time.

The CLI can open either role directly:

java -jar target/jdoor-assist-1.0.0-all.jar --host --port 8443
java -jar target/jdoor-assist-1.0.0-all.jar --host --advertise 192.168.1.50
java -jar target/jdoor-assist-1.0.0-all.jar --join "jdoor://…"
java -jar target/jdoor-assist-1.0.0-all.jar --help

Security model

sequenceDiagram
    participant H as Host
    participant V as Viewer
    H->>V: Pairing link via trusted channel
    V->>H: TLS handshake with endpoint identity + certificate pin
    V->>H: Single-use token + visible device name
    H->>H: Local consent prompt
    H-->>V: Approved, view-only session
    H-->>V: Optional control permission
    H->>H: Visible audit + immediate revoke

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The direct connection is intended for a trusted LAN. JDoor Assist does not include a public relay, NAT traversal, account system, or centralized trust service. Do not expose port 8443 directly to the internet. See the threat model and security policy before deploying it in a sensitive environment.

Build and package

mvn verify compiles with -Xlint:all -Werror, runs unit and real loopback TLS integration tests, creates a coverage report, builds the shaded JAR, and produces a CycloneDX SBOM.

Create an unsigned platform app image with JDK jpackage:

.\scripts\package.ps1

./scripts/package.sh

Outputs are written below target/package/. Community builds are currently unsigned; your OS may show an unverified-publisher warning. Release automation also emits checksums, an SBOM, and GitHub build provenance.

Repository map

src/main/java/com/jdoor/
├── audit/       local, secret-free security events
├── capture/     bounded JPEG screen capture
├── cli/         headless-safe command parsing
├── control/     policy-gated AWT input
├── protocol/    versioned and size-limited wire format
├── security/    ephemeral TLS identity, pinning, pairing token
├── session/     host/viewer lifecycle and consent boundary
└── ui/          launcher, host, and viewer desktop surfaces

Further reading:

• Architecture
• Threat model
• Privacy
• Development guide
• Contributing
• Changelog

License and attribution

JDoor remains licensed under GNU GPL v3. The original school project and its Git history are preserved to credit both collaborators. Portfolio material must distinguish that shared 2022 work from Djenis Ejupi’s later product, security, UX, testing, and release modernization.