Senior Applied Cryptography Engineer (80–100%)

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.Senior Applied Cryptography Engineer (80–100%)Your RoleAs an applied cryptography engineer at Threema, you will help us design, build, and scrutinize the cryptographic protocols behind our messenger, and contribute to the effective privacy protection of millions of people.Your TasksProtocol design and quantum-safe migration:Develop and specify cryptographic communication protocolsDesign cryptographic systems, such as key management and multi-device synchronizationLead Threema’s migration to quantum-safe cryptography, together with the cryptography researchers at IBM ResearchOwn threat modeling for new product features and protocol designs, in close collaboration with the product and engineering teamsSecurity analysis:Analyze protocols, algorithms, and implementations for security weaknesses, and assess what new attack vectors mean for our productsAssess the vulnerability reports that reach us through our bug-bounty partner and coordinate the fix with the engineering teamsResearch and community:Follow current developments in applied cryptography and turn relevant findings into concrete product improvementsMaintain contacts with the security research community and, if you enjoy it, represent Threema at conferencesYour SkillsDegree in computer science, mathematics, or information security, ideally with a focus on cryptography, or equivalent practical experienceSolid understanding of modern cryptographic primitives (AEAD, key exchange, KDFs, digital signatures) and of how they fail when combined incorrectlyWorking knowledge of key encapsulation mechanisms and of post-quantum cryptography, including hybrid constructions such as X25519MLKEM768Experience designing or reviewing security protocols, ideally in end-to-end encryption, key agreement, or multi-device settingsYou write code yourself, in at least one of Rust, Kotlin, Swift, TypeScript, or something comparableExperience reviewing implementations for side channels, nonce reuse, misuse-prone APIs, and similar problemsNice to have: practical experience with hybrid post-quantum handshakes, formal protocol verification, published research, or CVEs, experience with coordinated vulnerability disclosureExperience with AI toolsYou’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 designWhatever tools you use, the outcome is yours; AI can draft and suggest, but the person accountable for a protocol that holds is youSoft skillsStrong sense of responsibility, precise way of workingYou can write a protocol specification that someone else can implement, and explain a cryptographic trade-off to people who are not cryptographersPragmatic judgment about when a design is good enough to ship and when it is notWillingness to have your own designs picked apart, and to pick apart other people’s with careGood written and spoken English (at least B2), German is a nice-to-haveWhat We OfferA young, motivated team with straightforward communicationFlexible working hours, option to work from home up to two days per weekOption to work from anywhere for two weeks per yearOption to take unpaid leaveYou can choose your own hardware (macOS or Linux)Public transportation discount or parking space (electric car charging available)Free use of fitness room, including a fitness trainer once a monthProfessional massage once a monthInternal German or English coursesA great coffee machine ;-)Regular company events and aperitifsThe good feeling of contributing to the effective protection of the privacy of millions of peoplePlace of work: Pfäffikon SZ (Greater Zurich Area)Start date: Immediately or by agreementWe believe that diverse teams build better products. We welcome and encourage applications from people of all backgrounds, and perspectives.Your unique experience is an asset, and we’d love to hear from you. #J-18808-Ljbffr