Modern society is faced with a fundamental problem: the reliability of complex, evolving software systems on which society critically depends cannot be guaranteed by the established, non-mathematical computer engineering techniques such as informal prose specification and ad hoc testing. The situation is worsening: modern companies are moving fast, leaving little time for code analysis and test...

Proof Carrying Code (PCC) is a technique to exclude safety errors in low level code. Instead of runtime tests, it statically checks a proof of safety (a certificate) attached to the code. To guarantee that PCC only accepts safe code, we formalise and verify it in Isabelle/HOL, an interactive theorem prover for higher order logic. In an abstract framework we identify key components and their int...