Member of Technical Staff - Security Engineering in Bristol

Fractile was founded in 2022 on the bet that the world’s most capable AI systems would be limited in their impact by the time taken to produce useful outputs. We have been building chips and systems that tackle the problem of efficiently generating output at thousands of tokens per second while handling the complexity and capacity challenges of operating large models at very long contexts.

The role involves building the control chain that powers on, monitors, updates, and protects devices and racks across bare metal, RTOS, and embedded Linux. Security runs through all of it, creating a chain of trust from the hardware up to the rack management plane. You will be deeply involved in that security across the chain, making it real in software.

You’ll work hand in hand with our architecture and hardware teams, turning threat models into concrete mechanisms in bare metal, RTOS, and Linux, then designing, prototyping, and validating them. We want engineers who understand security from the inside out, knowing how the root of trust, boot chain, key hierarchy, and secure interconnects actually work under the hood.

What you’ll do:

• Shape the security of the control chain (device, board, chassis, and rack controllers): threat models, trust boundaries, and a coherent secure-by-design approach across all platforms.
• Design and help build secure boot and the root of trust on each controller: verified/measured boot, signing and verification, anti-rollback, and locking down debug and privileged access in production.
• Secure the interconnects, between controllers and between devices and the host, with authentication, integrity, and additional protections where needed.
• Design and build the cryptographic mechanisms: key hierarchies, provisioning and storage, device identity, and remote attestation.
• Make firmware updates safe end to end: signed images, rollback protection, staged rollout, and clean recovery, across every hop of the chain.
• Protect the running system, not just boot: harden the host Linux kernel and the on-die firmware.
• Work closely with hardware and the rest of the software team to build security into the product, running threat-model reviews, triaging vulnerabilities, and driving fixes to closure.

What we’re looking for:

• An adversarial mindset and sharp threat-modeling instincts: trust boundaries, assets, attacks, and honesty about residual risk.
• Hands-on experience with core security primitives in software and in silicon: secure boot, root of trust, cryptography, and key management.
• Secure protocol and channel design between components.
• Strong C and Rust skills, with an instinct for memory safety and defensive coding.
• Experience building security mechanisms: a secure-boot chain, key hierarchy, or attestation flow you shaped.

We get especially curious about your application when you also bring some of the following:

• Attestation at boot and at runtime, and management-plane protocols.
• Hardware building blocks and firmware/Linux hardening.
• Assurance and resistance: supply-chain security, fuzzing and testing, standards awareness.
• AI/LLM-assisted security tooling, and RISC-V / GPU / ML-accelerator experience.

This is a young company doing hard things, balanced across hardware and software. You’ll often be securing systems ahead of the hardware, reasoning about a threat model against a specification first, then a simulator, then early boards. You’ll work with incomplete information and watch it get sharper with every iteration.

We want a team that reflects the world it’s built for, and we welcome applicants from every background. We care that you’re excited by this kind of work, that you bring security rigour, and that you make a team better.

What We Offer:

• Competitive salary reflective of your experience and the specialist nature of the role.
• Meaningful equity so everyone shares in the value creation.
• Benefits: Private Medical, Dental and Vision, Contributory Pension, 25 Days holiday plus bank holidays and Life/Critical Illness Insurance.
• Diverse & fun office environment committed to Equal Employment Opportunity.

Fractile is seeking to increase the clock speed of global progress, one chip at a time. Join us!

Export controls: Our work involves technologies subject to UK, US and other international export control regulations. Certain roles may require additional eligibility checks to ensure compliance with applicable law.