International Association
for Cryptologic Research

A (k; n) threshold secret image sharing scheme, abbreviated as (k; n)-TSISS, splits a secret image into n shadow images in such a way

that any k shadow images can be used to reconstruct the secret image

exactly. In 2002, for (k; n)-TSISS, Thien and Lin reduced the size of each

shadow image to 1/k of the original secret image. Their main technique

is by adopting all coefficients of a (k-1)-degree polynomial to embed the secret pixels. This benet of small shadow size has drawn many researcher\'s attention and their technique has been extensively used in

the following studies. In this paper, we rst show that this technique

is neither information theoretic secure nor computational secure. Furthermore, we point out the security defect of previous (k; n)-TSISSs for

sharing textual images, and then fix up this security defect by adding an

AES encryption process. At last, we prove that this new (k; n)-TSISS is

computational secure.