M.Sc Thesis

M.Sc StudentAvraham Uri
SubjectABC - A New Framework for Symmetric Block Ciphers
DepartmentDepartment of Computer Science
Supervisors PROF. Eli Biham
DR. Orr Dunkelman
Full Thesis textFull thesis text - English Version


There is no arguing about the importance of encryption in today's world. We make frequent use, sometimes unaware, of encryption. We encrypt information that we send over the Internet, cellular phone calls, cable broadcasts, and more.

A large portion of this encryption is done using block ciphers. Block ciphers provide us with fast encryption, and can be used as building blocks of various encryption schemes (called modes of operation).

Block ciphers have always conformed to a specific interface with two inputs -- a plaintext block to encrypt and a key -  resulting in a ciphertext block of the same size as the plaintext block.

In this thesis we suggest a new framework for block ciphers named Advanced Block Cipher, or shortly ABC. This framework defines a new interface, and new modes of operation. ABC introduces two additional non-secret parameters that ensure that each call to the underlying block cipher behaves like a different pseudo-random permutation. It therefore ensures that attacks that require more than one block of encrypted data cannot apply. In particular, this framework protects against dictionary attacks, differential and linear attacks, and eliminates the weaknesses of most modes of operation. This new framework shares a common structure with the HAIFA hash function framework, and can share the same logic with HAIFA compression functions. We analyze the security of several modes of operation for ABCs block ciphers, and suggest several instances of ABCs.