Two-Server Password-Only Authenticated Key Exchange

Typical protocols for password-based authentication assume a single server which stores all the information (e.g., the password) necessary to authenticate a user. Unfortunately, an inherent limitation of this approach (assuming low-entropy passwords are used) is that the user’s password is exposed if this server is ever compromised. To address this issue, it has been suggested to share a user’s password information among multiple servers, and to have these servers cooperate (possibly in a threshold manner) when the user wants to authenticate. We show here a two-server version of the password-based key-exchange protocol of Katz, Ostrovsky, and Yung (the KOY protocol). Our work gives the first provably-secure two-server protocol for the password-only setting (in which the user need remember only a password, and not the servers’ public keys), and is the first two-server protocol (in any setting) with a proof of security in the standard model. Our work thus fills a gap left by th...

• Type: Conference
• Year: 2005
• Where: ACNS
• Authors: Jonathan Katz, Philip D. MacKenzie, Gelareh Taban, Virgil D. Gligor
• Keywords: ACNS 2005, Cryptography, KOY Protocol, Password-based Key-exchange Protocol, User’s Password