Tom Cosgrove
Principal Software Engineer at Arm
London, England, United Kingdom
Summary
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Rockstar🎓
Top SchoolTom Cosgrove is a Principal Software Engineer based in London with over two decades of systems and security experience and five years in senior engineering roles focused on cryptography and low-level C development. He currently leads architecture and security work at Arm, having progressed through staff and principal engineering roles while contributing deeply to open-source crypto stacks like OpenSSL and Mbed TLS. His contributions include fixing critical vulnerabilities, optimizing AES and SHA implementations for AArch64 and Apple Silicon, and resolving subtle cross-compiler and sanitizer issues—work that improves both performance and real-world security. Tom blends a physics-trained analytical mindset from Oxford with practical embedded and kernel-space experience dating back to OpenBSD and Symbian, making him comfortable in constrained, performance-sensitive environments. Outside work he’s engaged in sports tech and cycling, a personal interest that informs his pragmatic approach to instrumentation and real-time systems.
5 years of coding experience
22 years of employment as a software developer
MA, Physics, MA, Physics at University of Oxford
Github Skills (26)
algorithm10
crypto10
assembly10
ssl10
tls1210
sha10
it-security10
c1110
tls1310
security10
crypt10
c1710
mtls10
cryptography10
aes10
Programming languages (4)
Github contributions (5)
Mbed-TLS/mbedtls
Nov 2021 - Jan 2023
An open source, portable, easy to use, readable and flexible TLS library, and reference implementation of the PSA Cryptography API. Releases are on a varying cadence, typically around 3 - 6 months between releases.
Role in this project:
Security Engineer
Security EngineerContributions:2542 reviews, 159 commits, 249 PRs in 1 year 2 months
Contributions summary:Tom primarily focused on enhancing the security of the mbedtls library by adding and optimizing cryptographic primitives, specifically for SHA-256 and SHA-512. Their contributions include the implementation of A64 crypto extensions, which leverage ARM architecture features for accelerated hashing. The user also refactored code to align with Mbed TLS coding standards and addressed minor code quality and documentation issues. This work significantly enhances the performance and security of the core cryptographic functionalities.
cryptography-libraryapisslcryptographycryptography-api
openssl/openssl
May 2021 - Dec 2022
TLS/SSL and crypto library
Role in this project:Back-end Developer & Security Engineer
Back-end Developer & Security EngineerContributions:954 reviews, 19 commits, 38 PRs in 1 year 6 months
Contributions summary:Tom primarily contributed to the OpenSSL library by addressing security vulnerabilities and optimizing code for various ARM architectures, including AArch64 and Apple Silicon. Their work involved fixing build issues, improving branch target indications, and ensuring correct handling of signed bit shifts, particularly when using sanitizers. They also implemented performance enhancements and bug fixes related to AES and other cryptographic functions. Furthermore, the user addressed issues related to IPv6 configurations and the `ldr` pseudo-instruction, showcasing a focus on code correctness and optimization across different compiler environments and architectures.
crypto-librarycryptographyssltlscrypto
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