It is a kind of extension of the idea of secret-sharing protocols and is in part based on Shamir’s secret-sharing algorithm. What distinguishes Secret Chats Protocol from the classic version of the secret split is adding new participants to an already existing partition. It became possible thanks to appropriate mathematical methods and the construction of the algorithm itself.
The main goal behind the creation of Secret Chats Protocol was straightforward – to allow mobile messaging users to have multiple dimensions (levels) of protection. Each dimension stores confidential data for the user, such as various text conversations, contact groups, or multimedia files. Access to the security dimensions is obtained by the user, e.g. by using different passwords. A separate password protects each protection dimension, and only the user knows how many protection dimensions have been created. An additional, significant feature of Secret Chats Protocol is the protection of the number of dimensions. As a result, a potential attacker does not know how many different protection dimensions the user has defined in the application.
The main idea behind the Secret Chats Protocol algorithm is to recover/use two secrets. The first of them is common and the same for each protection dimension. It is obtained from the password associated with the data protection dimension using the proposed mechanism for dividing the secret. This secret can be used in applications to secure general application data by creating an encryption key for the SQLCipher secure data storage mechanism. The second secret is obtained using the PBKDF mechanism based on a password provided by the user. This secret is different for different dimensions of information protection, and it can be used in the application to protect information related to a given dimension.
Secret Chats Protocol is a general concept of a multi-dimensional protection mechanism that can be successfully applied to many different solutions and applications.
The study’s authors are Kamil Kaczyński and Michał Glet from the Military University of Technology in Warsaw.