PDKE-G: A Bio-Inspired Contributory Group Authenticated Key Exchange Grounded in Per-Member AlphaFold2 Protein...

Authenticated key exchange underpins secure communication, yet the structural complexity of biological macromolecules has rarely served as cryptographic material. The recently proposed Protein-Derived Key Exchange (PDKE) protocol binds AlphaFold2-predicted protein geometry to ephemeral elliptic-curve Diffie-Hellman for two parties. We introduce PDKE-G, a contributory group authenticated key exchange in which each member's signing credential is derived from its protein geometry as a member-specific input: the long-term signing key is extracted with HKDF from the protein's Cα-Cα distance matrix keyed by a per-member 128-bit secret seed, and a constant-round Burmester-Desmedt core wrapped by the Katz-Yung compiler with these protein-derived signatures yields a shared 256-bit session key with forward secrecy. We give a computational proof of security under Decisional Diffie-Hellman, KDF security of HKDF, pseudorandomness of the credential derivation, and strong unforgeability (SUF-CMA) of the signature, in the random-oracle model for the hash-to-curve and SHA-256 maps, and we verify the three- and four-party instantiations symbolically in ProVerif. Because every broadcast carries a per-member certified signature bound to the session context, PDKE-G prevents the honest-member insertion attack of the member-tampering setting within the scope of Corollary 1. An empirical study of 519 AlphaFold structures across seven organisms finds their canonical geometry descriptors all distinct, with a mean of 12.3 descriptive Shannon bits per residue pair. Because the selection space of known proteins is only about 2^27.7, identity is anchored by the certified public key and the secret seed, which supplies the credential's brute-force security. The protocol completes in a constant number of rounds independent of group size, with a logical-broadcast message count that is linear in the number of members; over point-to-point links both PDKE-G and pairwise composition are Θ(n²) in raw transmissions, so the advantages are the constant round count and the single contributory group key.