Nowadays, due to the widespread use of different web services users are getting more and more defenceless, as more and more information gets shared about them mainly with web service providers. These providers not only observe the activities of their users, but they also build databases about typical activities, fields of interest etc. based on the personal contents shared by the users. This phenomenon makes the protection of the users' private sphere crucial.
Google as one of the biggest web service providers owns a tremendous amount of information about its users – due to the extraordinary popularity of Gmail developed and maintained by them, they can even easily access the private mailings of the users. The main reason of the popularity of Gmail is that several convenient and in many ways practical options are provided in order to manage the complete mailing of the users. That's the exact reason why it's crucial for any application aiming to protect the private mails in the Gmail system to keep the easy usage and to support the given functions as well.
In this work I designed and implemented a software module which allows users to take full advantage of the functionality Gmail has to offer – even the default practical keyword search function provided basicly by Gmail – in a way that their private mailings remain hidden from even the provider. Using the presented software module one can store their mails encrypted using the Gmail mailbox, and also encrypted communication with their mail partners is also provided, with all the mails still readable and searchable for the user.
In my thesis I present the structure of the implemented system, the most important steps of the implementation and I introduce the functioning and results of the testing of it. Moreover, I explain the cryptographic methods used in the construction of the software module and the algorithms enabling the storage and transfer of encrypted messages and searching by keywords.