Dual-workfactor Encrypted Key Exchange: Efficiently Preventing Password Chaining and Dictionary Attacks

Password-based key-server protocols are susceptible to password chaining attacks, in which an enemy uses knowledge of a user's current password to learn all future passwords. As a result, the exposure of a single password eeectively compromises all future communications by that user. The same protocols also tend to be vulnerable to dictionary attacks against user passwords. Bellovin and Merritt1] presented a hybrid of symmetric-and public-key cryptography called En-crypted Key Exchange (EKE) that cleanly solves the dictionary attack problem. This paper presents an extension of their ideas called dual-workfactor en-crypted key exchange that preserves EKE's strength against dictionary attacks but also eeciently prevents passive password-chaining attacks.