Structural Properties of Cryptographic Sequences - Computational Intelligence in Security for Information Systems - page 151

Keeping Group Communications Private: An
Up-to-Date Review on Centralized Secure
Multicast

J.A.M. Naranjo and L.G. Casado

Dpt. of Computer Architecture and Electronics,
University of Almerıa, Spain
{ jmn843,leo } @ual.es

Abstract. The secure multicast field has been extensively studied for
more than a decade now and there exist numerous proposals throughout
academic literature. This paper presents a selection of those most im-
portant and popular to the date, focusing on centralized schemes due to
their high popularity and the recent publication of alternatives that do
not appear in previous revisions. Comparisons are provided and special
attention is paid to communications and storage overhead.

Keywords: key distribution, secure group communication, centralized
secure multicast.

1 Introduction

Secure multicast communications imply establishing a common encryption key
that can be used to cipher the transmitted information. The first and trivial
approach for achieving that is to establish n secure channels (one for each re-
cipient), which obviously soon becomes impractical as the number of recipients
scales. Therefore a wide variety of schemes have appeared in the last decade.
Regardless of their nature, schemes must provide: information privacy while in
transit, an ecient and fault-tolerant rekeying process so an acceptable quality
of service (QoS) is guaranteed, and forward and backward secrecy .Theformer
implies that a member which leaves the network (i.e., her membership expires)
should not be able to decrypt any ciphered information transmitted thereafter,
while the latter implies that an arriving member should not be able to decrypt
any ciphered information transmitted before her arrival. Both impose a refresh-
ment of the encryption key used to cipher the transmitted information. These two
restrictions may become an eciency problem at high churn rates (avalanches of
members joining and/or leaving). Some less restrictive scenarios may not require
backward secrecy. Additionally, schemes must be resistant to col lusion , i.e., old
recipients allying together to use their expired key material in order to illegally

J.A.M. Naranjo and L. G. Casado are supported by the Spanish Ministry of Science
and Innovation (TIN2008-01117). L. G. Casado is also supported by funds of Junta
de Andalucıa (P08-TIC-3518).