Cryptographic algorithms, protocols, and applications are difficult to implement correctly, and errors and vulnerabilities in their code can remain undiscovered for long periods before they are exploited. Even highly-regarded cryptographic libraries suffer from bugs like buffer overruns, incorrect numerical computations, and timing side-channels, which can lead to the exposure of sensitive data and longterm secrets. We describe a tool chain and framework based on the the F * programming language to formally specify, verify and compile high-performance cryptographic software that is secure by design. This tool chain has been used to build a verified cryptographic library called HACL * , and provably secure implementations of sophisticated secure communication protocols like TLS and Signal. We describe these case studies and conclude with ongoing work on using our framework to build verified implementations of privacy preserving machine learning systems.