**BROADCAST ENCRYPTION $\pi$**

*Nam-Su Jho, Jung Hee Cheon, Myung-Hwan Kim, and Eun Sun Yoo*

**Abstract: **We propose a new broadcast encryption scheme $\pi$ based on the
idea of `one key per each punctured interval'. Let $N$ and $r$ be
the numbers of total users and revoked users, respectively. In our
scheme with $p$-punctured $c$-intervals, the transmission overhead
is asymptotically {\normalsize$\frac r{p+1}$} as $r$ grows. We
also introduce two variants of our scheme to improve the
efficiency for small $r$. Our scheme is very flexible with two
parameters $p$ and $c$. We may take $p$ as large as possible if a
user device allows a large key storage, and set $c$ as small as
possible if the storage size and the computing power is limited.
Our scheme also possesses another remarkable feature that any
number of new users can join at any time without key refreshment,
which is not possible in other known practical schemes.

**Category / Keywords: **applications / Broadcast Encryption, revocation, one-way function, punctured interval

**Publication Info: **Proceedings of Eurocrypt '05

**Date: **received 4 Mar 2005

**Contact author: **drake at math snu ac kr

**Available format(s): **Postscript (PS) | Compressed Postscript (PS.GZ) | PDF | BibTeX Citation

**Note: **This paper is the original version that we submitted to Eurocrypt'05. In the proceedings, the merged version of this paper with another paper(submitted by Hwang and Lee of Korea Univ.) will appear.

**Version: **20050308:103609 (All versions of this report)

**Short URL: **ia.cr/2005/073

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