Mobile Ad hoc Networks (MANETs) are deployed in many new domestic and public applications, contributing to new requirements in terms of performance and efficiency. However due to their nature, some usual network services such as routing and security are not carried out as well as expected. Securing routing protocols is one of these challenging tasks, since security is not natively implemented in ad hoc routing, and the extensions given in the literature are complex and vulnerable against several attacks. Therefore in this paper, we propose an implementation of public key infrastructure (PKI) exploiting the route discovery and route reply mechanisms of reactive routing protocols to publish self-issued certificates in a distributed fashion. These certificates are used by mobile nodes to secure communications, ensure authentication, integrity, confidentiality, and detect attacks in mobile ad hoc networks. Our proposed scheme is simple and utilizes the underlying protocol as a support for certificate publishing; therefore it does not affect the performance of the network. In addition, all the operations in our scheme are performed in the network layer making it useful for heterogeneous networks since it has no additional relation with other network layers such as MAC and PHY