XMSS-based Chain of Trust

Given that large-scale quantum computers can eventually compute discrete logarithm and integer factorization in polynomial time [44], all asymmetric cryptographic schemes will break down. Hence, replacing them becomes mandatory. For this purpose, the Na- tional Institute of Standards and Technology (NIST) initiated a standardization process for post-quantum schemes. These schemes are supposed to substitute classical cryptography in different use-cases, such as client-server authentication during the TLS handshake. How- ever, their signatures, public key sizes, and signature verification time impose difficulty, especially for resource-constrained devices. In this paper, we improve the TLS hand- shake performance relying on post-quantum signatures by combining the XMSS and the Dilithium signature schemes along the chain of certificates. We provide proof-of-concept implementation of our solution by integrating the two signature schemes in the WolfSSL library. Moreover, we evaluate the performance of our solution and establish that it re- duces the signature verification time considerably and minimizes the size of the chain of trust. We provide a security proof of the proposed chain of trust which is relies on the security of the XMSS scheme.