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 National 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. However, their signatures, public key sizes, and signature verification time impose difficulty, especially for resource-constrained devices. In this paper, we improve the TLS handshake 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 reduces 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.