## CryptoDB

### Eun Sun Yoo

#### Publications

Year
Venue
Title
2007
EPRINT
This paper proposes fully resilient traitor tracing schemes which have no restriction about the number of traitors. By using the concept of key update, the schemes can make the pirate decoders useless within some time-period, which will be called life-time of the decoder. There is a trade-off between the size of ciphertext and life-time of pirate decoders.
2005
EUROCRYPT
2005
EPRINT
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.
2005
EPRINT
We develop a couple of new methods to reduce transmission overheads in broadcast encryption. The methods are based on the idea of assigning {\it one key per each partition using one-way key chains} after partitioning the users. One method adopts {\it skipping chains} on partitions containing up to $p$ revoked users and the other adopts {\it cascade chains} on partitions with layer structure. The scheme using the former reduces the transmission overhead down to $\frac r{p+1}$ asymptotically as $r$ grows, and the scheme using the latter keeps the transmission overhead very small when $r$ approaches 0, where $r$ is the number of revoked users. Combining the two schemes, we propose a new broadcast encryption scheme with least transmission overhead. Our schemes also possess a remarkable feature that any number of new users can join at any time without key update, which is not available for most of known practical schemes.

#### Coauthors

Jung Hee Cheon (3)
Jung Yeon Hwang (1)
Nam-Su Jho (3)
Myung-Hwan Kim (4)
Dong Hoon Lee (1)
Koutarou Suzuki (1)