This paper presents an approach to the verification of large Java programs. The focus lies on programs that implement a distributed communicating system e.g. in a Mor E-Commerce scenario. When trying to verify such programs, thousands of Java classes with tens of thousands of lines of code would have to be taken into consideration. That is impossible. The paper introduces a technique that dramatically reduces the amount of source code that must be considered. Additionally, a suitable method for programming security critical systems is introduced. The reduction is achieved by extracting a verification kernel from the program, which is sufficient for proving the correctness of the relevant part. An algorithm for the automatic computation of the verification kernel has been developed and is presented in the paper. The correctness of the verification kernel approach is proved on the level of the Java language semantics.