Post-Quantum Security of Messaging Protocols: Analysis of Double Ratcheting Algorithm

Development in the area of quantum technologies led to the appearance of first quantum computers. The threat of using a quantum computer for cryptanalysis requires wide implementing post-quantum security in computing algorithms and communication protocols. We evaluate the computational power of some existing quantum computers to illustrate the relevance of research in post-quantum security. One of the best ways to test post-quantum protocols is to embed them into some non-critical but widely-used sphere. Secure messaging is an excellent example of such an application. In the paper, we analyze the post-quantum security of well-known messaging specification Signal, which is considered to have high-security properties. The core of Signal specification is the Double Ratchet protocol. We notice and explain why it is not a post-quantum secure scheme. After that, we suggest some possible ways to improve the security features of Signal specification.