We describe the design and implementation of signed executables for Linux, which provide the following strong integrity guarantees: the inability to tamper with executables and the inability to add new unauthorized executables. Unlike other implementations, ours covers statically and dynamically linked executables as well as executable scripts. In addition, we reduced the overhead of signature verification to almost zero by caching the successful verification results. The negligible overhead enables signature verification to be used as a basic building block for other applications of which some are described in this paper. Also UMIACS-TR-2001-41