The OSGi platform is a lightweight management layer over a Java virtual machine that makes runtime extensi- bility and multi-application support possible in mobile and constraint environments. This powerfull capability opens a particular attack vector against mobile platforms: the in- stallation of malicious OSGi bundles. The first countermea- sure is the digital signature of the bundles. We developed a tool suite that supports the signature, the publication and the validation of the bundles in an OSGi framework. Our tools support the publication of bundles onto a remote bun- dle repository as well as the validation of the signature ac- cording to the OSGi R4 specifications. A comparison of ex- isting validation mechanisms shows that our security layer is the only one that is compliant with the specification.