We report on a solution we designed for the VerifyThis Collaborative Long Term Challenge 2019. We used the Why3 verification framework to design, from scratch, a simple but running prototype implementation of a PGP key server. We exploit the ability of Why3 to extract OCaml code from verified WhyML code so as to produce code that can be compiled into an executable. Our prototype is made of a combination of unverified handwritten OCaml code and of WhyML code whose functional behaviour is formally specified and proven correct.