Senior Applied Cryptography Engineer

Wer wir sind

Threema is the world’s best-selling secure messenger for both private users and businesses. Since 2012, we have been working tirelessly to ensure that our users can communicate freely without worrying about their privacy. Our growing user base includes millions of private customers and thousands of businesses and organizations from all over the world.

Your Tasks

• Develop and specify cryptographic communication protocols
• Design cryptographic systems, such as key management and multi-device synchronization
• Lead Threema’s migration to quantum-safe cryptography, together with the cryptography researchers at IBM Research
• Own threat modeling for new product features and protocol designs, in close collaboration with the product and engineering teams
• Analyze protocols, algorithms, and implementations for security weaknesses, and assess what new attack vectors mean for our products
• Assess the vulnerability reports that reach us through our bug-bounty partner and coordinate the fix with the engineering teams
• Follow current developments in applied cryptography and turn relevant findings into concrete product improvements
• Maintain contacts with the security research community and, if you enjoy it, represent Threema at conferences

Your Skills

Experience with AI tools: Cryptography and engineering: Soft skills:

• Degree in computer science, mathematics, or information security, ideally with a focus on cryptography, or equivalent practical experience
• Solid understanding of modern cryptographic primitives (AEAD, key exchange, KDFs, digital signatures) and of how they fail when combined incorrectly
• Working knowledge of key encapsulation mechanisms and of post-quantum cryptography, including hybrid constructions such as X25519MLKEM768
• Experience designing or reviewing security protocols, ideally in end-to-end encryption, key agreement, or multi-device settings
• You write code yourself, in at least one of Rust, Kotlin, Swift, TypeScript, or something comparable
• Experience reviewing implementations for side channels, nonce reuse, misuse-prone APIs, and similar problems
• Nice to have: practical experience with hybrid post-quantum handshakes, formal protocol verification, published research, or CVEs, experience with coordinated vulnerability disclosure
• You’re familiar with current frontier AI models and use them as a productivity multiplier in design work as well as in coding, for example to review specification drafts, survey recent literature, or poke holes in a protocol design
• Whatever tools you use, the outcome is yours; AI can draft and suggest, but the person accountable for a protocol that holds is you
• Strong sense of responsibility, precise way of working
• You can write a protocol specification that someone else can implement, and explain a cryptographic trade-off to people who are not cryptographers
• Pragmatic judgment about when a design is good enough to ship and when it is not
• Willingness to have your own designs picked apart, and to pick apart other people’s with care
• Good written and spoken English (at least B2) , German is a nice-to-have

Fähigkeiten

RustKotlinSwiftTypeScript

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