Senior Applied Cryptography Engineer

As a Senior Applied Cryptography Engineer at Threema, you will help design, build and scrutinize the cryptographic protocols behind the world's best-selling secure messenger, contributing to the effective privacy protection of millions of people.

What you'll do

• 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 in collaboration with cryptography researchers at IBM Research
• Own threat modeling for new product features and protocol designs in close collaboration with product and engineering teams
• Analyze protocols, algorithms and implementations for security weaknesses and assess what new attack vectors mean for Threema's products
• Assess vulnerability reports through the bug bounty program and coordinate fixes with engineering teams
• Follow developments in applied cryptography and turn relevant findings into concrete product improvements
• Maintain contacts with the security research community and represent Threema at conferences if you enjoy it

What you bring

• A 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 how they fail when combined incorrectly
• Working knowledge of key encapsulation mechanisms and 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
• The ability to write code 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
• Strong sense of responsibility and a precise way of working
• The ability to write a protocol specification that someone else can implement and explain cryptographic trade-offs to non-cryptographers
• Pragmatic judgment about when a design is good enough to ship and when it is not
• Willingness to have your designs picked apart and to pick apart others' designs with care
• Good written and spoken English (at least B2 level)
• Familiarity with current frontier AI models and the ability to use them as a productivity multiplier in design and coding work

Nice to have

• Practical experience with hybrid post-quantum handshakes
• Experience with formal protocol verification
• Published research or CVEs
• Experience with coordinated vulnerability disclosure
• German language skills

What we offer

• Flexible working hours with the option to work from home up to two days per week
• Option to work from anywhere for two weeks per year
• Option to take unpaid leave
• Choice of your own hardware (macOS or Linux)
• Public transportation discount or parking space with electric car charging available
• Free use of fitness room including a fitness trainer once a month
• Professional massage once a month
• Internal German or English courses
• Regular company events and aperitifs

About Threema

Threema is the world's best-selling secure messenger for private users and businesses. Since 2012, the company has enabled millions of private customers and thousands of organizations worldwide to communicate freely without compromising privacy. The role is based in Pfäffikon SZ (Greater Zurich Area) with an immediate or flexible start date.