Abstract:
This paper presents the experience of verifying client implementations of the TLS cryptographic protocol version 1.3. TLS is a widely used cryptographic protocol today, designed to create secure data transmission channels. The protocol provides the necessary functionality for its tasks: confidentiality of transmitted data, data integrity, and authentication of the parties. In the new version 1.3 of the TLS architecture was significantly redesigned, eliminating a number of shortcomings of previous versions that were identified both during the development of implementations and during their operation. We used a new test suite for verifying client implementations of the TLS 1.3 for compliance with Internet specifications, developed on the basis of the RFC8446, using UniTESK technology and mutation testing methods. To test implementations for compliance with formal specifications, UniTESK technology is used, which provides testing automation tools based on the use of finite state machines. The states of the system under test define the states of the state machine, and the test effects are the transitions of this machine. When performing a transition, the specified impact is passed to the implementation under test, after which the implementation's reactions are recorded and a verdict is automatically made on the compliance of the observed behavior with the specification. Mutational testing methods are used to detect non-standard behavior of the system under test by transmitting incorrect data. Some changes are made to the protocol exchange flow created in accordance with the specification: either the values of the message fields formed on the basis of the developed protocol model are changed, or the order of messages in the exchange flow is changed. The protocol model allows one to make changes to the data flow at any stage of the network exchange, which allows the test scenario to pass through all the significant states of the protocol and in each such state to test the implementation in accordance with the specified program. The presented approach has proven effective in several of our projects when testing network protocols, providing detection of various deviations from the specification and other errors. The current work is part of the TLS 1.3 protocol verification project and covers TLS client implementations.