Multi-party pairwise key agreement in linear number of Diffie–Hellman key exchanges

Abstract

We consider a classical problem of multi-party pairwise key agreement (MP-KA): n parties wish to establish a secure communication channels to each other. Currently, this problem is easily solved with involvement of a trusted Key Distribution Center (KDC) or Key Translation Center (KTC), public key encryption or key pre-distribution protocols. But these solutions are not applicable when some parties are corrupted and all of them have only a link to the Certificate Verification Center (CVC). We develop MP-KA protocol without Trusted Setup and involvement of KDC or KTC, which reduces the number $$(n(n-1))/2$$ of Diffie–Hellman key exchanges (DH-KE). Precisely, for an adversary, who corrupts no more then t-out-of-n parties, $$t \le [n/2]-1$$ , we reduce this number to $$(n-t-1)\cdot (t+1)$$ , and thus to O(n) for the constant value of t. Our protocol consists of two phases: (1) $$k = (n-t-1)\cdot (t+1)$$ DH-KE runs to establish secure channels between a subset of all parties and (2) a protocol based on secret sharing, intended to agree on pairwise keys between other parties. We prove that the second phase of protocol is perfectly secure against semi-honest threshold adversary. As a result, we improve the efficiency of multi-party pairwise key agreement in comparison with direct Diffie–Hellman-based approach.