The Smart Grid has come to modernize the traditional electric power grid with applications which contribute to more effective power distribution and management with a more reliable manner in comparison with the ageing power grids of today. The deployment and use of the smart grid will have great social effects and benefits since the power distribution on demand makes it more eco-friendly, saves money, assists the fault handling and mitigates the unavailability to the electric power due to grid corruptions. But since it is based on a digital networked infrastructure it should be secure and the best way to prevent any incidents is to deploy technologies, systems and networks that are designed, developed and tested to achieve secure operation. One of the major security concerns in the smart grid is how the infrastructure will operate on a trusted basis, in order to assure its normal operation in terms of availability, integrity and confidentiality. There are numerous attacks for the smart grid which could mitigate the availability of the utility’s control systems with various consequences or to lead to incorrect billing and data theft or to affect the communication protocols that are used in the smart grid. Let’s say that a smart meter, which is an advanced meter that measures with high precision the power consumption, wants to send the data back to the utility for load balancing and billing purposes. The utility should trust the specific smart meter in order to take into account the information that receives from it, otherwise to exclude the data and take further actions for the malicious node. It becomes necessary to establish a trust management scheme on the smart grid which will facilitate the power electric utility to accumulate the data and to establish secure communications. This master thesis deals with the problem of the key management in the smart grid in order to establish trust among the participants of the network. A standard solution of a Trust management scheme is using a Public Key Infrastructure which brings many tradeoffs due to its centralized architecture and the way that the certificates are produced and maintained. In order to maintain the operation of the system in case of a centralized PKI failure and mitigate the costs we examine the solution of the Web-of-Trust reputation concept in the smart grid which could coexist with a PKI solution. This solution is built on top of a Distributed Hash Table for efficient lookups of trust relationships and has been simulated with the Oversim P2P network simulation framework which is part of the Omnet++ simulation environment. Following, we study the concepts presented above, how they can work all together and how the solution simulated in the network simulator.