C# Software Engineer – Windows Systems & Security

Untethered Labs, the team behind GateKeeper—an enterprise authentication and credential-management platform used worldwide in healthcare, government, and enterprise environments—is looking for a full-time C# Software Engineer to join us on-site at our headquarters in Greenbelt, MD.

We are actively modernizing and expanding the entire GateKeeper ecosystem, from the Windows Credential Provider to our multi-tenant cloud infrastructure, native Windows services, secure communication layers, BLE/NFC token management, passkey support, browser extension integration, and high-performance Azure back-end services.

If you enjoy solving hard technical problems, working close to the OS, and building secure, high-reliability systems used in critical environments, this role is for you.

The Role

You'll work alongside the lead engineer on the GateKeeper Windows client — the core product. This is a hands-on development role where you'll take ownership of subsystems and ship features that run on thousands of machines in critical environments.

We maintain detailed architecture documentation and design decisions across the codebase. You'll execute against those designs, contribute your own ideas, and use AI development tools as part of the daily workflow. You're not figuring out the architecture alone — but you're not just writing code to a spec either. You'll be expected to understand the systems you're working in, flag problems, and make good decisions within them.

What You’ll Work On

This is not regular CRUD development. You will be working across multiple layers of the product, including:

⭐ Windows Client Platform (C# / .NET 4.7 & .NET 8)

• Windows Service — lifecycle management, session handling, power events, background synchronization
• Credential Provider — WPF-based login UI on the secure desktop, COM interop, multi-step authentication wizards
• Secure IPC — Named Pipe architecture with process trust validation, event broadcasting, framed binary protocol
• Authentication — Kerberos, MSV1_0, and Negotiate logon flows via LSA, cached credential validation, domain reachability
• Hardware — BLE adapter management, NFC/RFID smart card readers via WinSCard API, serial port communication
• Security — DPAPI encryption, cryptographic operations, certificate management

⭐ High-Performance System Design

• Low-latency authentication paths (sub-100ms targets)
• Advanced caching strategies (SQLite, LiteDB, encrypted file-based stores)
• Robust offline login support
• Domain reachability heuristics, DC discovery optimizations
• Diagnostics, service reliability, startup performance tuning

⭐ Security & Identity Engineering

• WebAuthn passkey support via browser extension and native messaging
• FIDO2 hardware authenticator integration
• Certificate-based Windows login via virtual smart card
• Enterprise VDI connectors (Citrix, VMware, RDP)
• Performance optimization in the credential provider and login pipeline
• Ongoing security hardening and code quality improvements

Required

• C# and .NET experience (2+ years shipping production code)
• Comfortable with async/await, multithreading, and concurrent data structures
• Experience building or maintaining Windows Services or desktop applications
• Can work in WPF — read XAML, debug binding issues, implement view models
• Strong debugging habits — you reach for diagnostics tools, logs, and profilers before guessing
• Experience with Git in a shared codebase
• Self-directed — you can take a design document and turn it into working code without daily hand-holding

Highly Preferred

• Experience with Windows security or identity APIs — DPAPI, certificate stores, Credential Providers, smart card APIs
• Experience with IPC — Named Pipes, RPC, or custom protocols
• Experience with SQLite, LiteDB, or encrypted local storage
• Experience with ASP.NET Core Web APIs
• Familiarity with CI/CD and build automation
• Comfort using AI coding tools as part of the development workflow

Bonus

• FIDO2 / passkeys / WebAuthn
• P/Invoke, COM interop, unsafe contexts
• Security-sensitive products in regulated environments
• Enterprise software at scale (thousands of endpoints)

Soft Skills

• Highly detail-oriented and comfortable with complex systems
• Passion for security, performance, and reliability
• Ability to troubleshoot deeply and think systematically
• Comfortable working in a fast-moving product team
• Strong communication skills — able to explain choices clearly
• Ownership mindset: you build it, you understand it, you improve it

Work Environment

• On-site at our Greenbelt, MD headquarters
• Small engineering team — you'll own entire subsystems from day one
• Fast decision cycles, no bureaucracy
• AI-augmented development workflow
• Direct access to customer feedback and production data

What We Offer

• Competitive salary and benefits package.
• Opportunity to work with a modern tech stack on exciting projects.
• Flexible working hours and remote work options.
• Direct ownership of features used in critical environments
• Your code runs on thousands of machines — you'll see the impact

About Us

Untethered Labs, Inc. is an identity and access management solutions company based out of Greenbelt, MD. Our product – GateKeeper – is a hardware and software solution for companies in Healthcare, Manufacturing, Law Enforcement, and others, providing real-time continuous authentication to workstations, web, and application credentials. GateKeeper has a top rating for product as well as support in several major enterprise review sites. Our team strives to provide the best product and support to our customers with 24/7 on time and zero service interruptions. Read more about our product at: https://gkaccess.com

If you are passionate about software development and eager to advance your skills in .NET technologies, we’d love to hear from you!

Job Type: Full-time

Pay: $90,000.00 - $110,000.00 per year

Benefits

• Dental insurance
• Flexible schedule
• Health insurance
• Paid time off

Work Location: In person