  Arithmetic Coding (AC) is widely used for the entropy coding of text and
video data. It involves recursive partitioning of the range [0,1) in accordance
with the relative probabilities of occurrence of the input symbols. A data
(image or video) encryption scheme based on arithmetic coding called as Chaotic
Arithmetic Coding (CAC) has been presented in previous works. In CAC, a large
number of chaotic maps can be used to perform coding, each achieving Shannon
optimal compression performance. The exact choice of map is governed by a key.
CAC has the effect of scrambling the intervals without making any changes to
the width of interval in which the codeword must lie, thereby allowing
encryption without sacrificing any coding efficiency. In this paper, we use a
redundancy in CAC procedure for secure multicast of videos where multiple users
are distributed with different keys to decode same encrypted file. By
encrypting once, we can generate multiple keys, either of which can be used to
decrypt the encoded file. This is very suitable for video distribution over
Internet where a single video can be distributed to multiple clients in a
privacy preserving manner.
