Abstract

Various cryptographic algorithms used in practice, including block ciphers,
stream ciphers, hash functions and modes of encryption, are heuristics in
the sense that they are not provably secure in general, but rather are
proven to be secure against specific attacks. There are underlying
constructions, such as Feistel Networks, with provable security properties
in theory, that can serve as a basis for the practical algorithms. We
discuss such constructions for block ciphers and modes of encryption that
support variable-length blocks and multiple blocks. Among these are Halevi
and Rogaway's CMC mode of encryption, and Bellare and Rogaway's
Variable-Input Length Ciphers. More recently, the Elastic Network,
introduced by Cook, Yung and Keromytis, has been proposed as a construction
for creating variable-length block ciphers that results in the computational
workload being proportional to the input length. We show how the elastic
network allows any fixed-length block cipher to be converted to a
variable-length block cipher (an elastic block cipher). We provide an
overview of the security analysis for elastic block ciphers and describe an
implementation of elastic version of AES. We also discuss applications of
elastic block ciphers, including database encryption and new modes of
encryption. Finally, we discuss proposals for how these constructions can be
utilized in the design of hash functions.

This is joint work with Moti Yung (Google Inc. and Columbia University) and Angelos
Keromytis (Columbia University). 


Speaker Bio:

Debbie Cook is a researcher at Alcatel-Lucent Bell Labs. Her
interests are focused in applied cryptography and security. Her
recent work includes block cipher design, hash function design,
usability factors of one-time password generators, phishing
detection and security event analysis. She has a M.S. and
Ph.D. in computer science from Columbia University in New York,
and a B.S. and M.S.E.  in mathematical sciences from the Johns
Hopkins University in Baltimore, Maryland. After graduating from
Johns Hopkins, she was a senior technical staff member at AT&T
Bell Labs and AT&T Labs before pursuing her Ph.D. At AT&T, she
worked on a variety of projects involving operations support
system design, network requirements for voice services, VoIP
security analysis and industry negotiations. She is also an
adjunct assistant professor at Columbia University and the New
Jersey Institute of Technology.