A visual cryptography scheme for a set $\cal P $ of $n$ participants is a method to encode a secret image $SI$ into $n$ shadow images called shares, where each participant in $\cal P$ receives one share. Certain qualified subsets of participants can ``visually'' recover the secret image, but other, ... more >>>

In this primarily expository paper, we discuss the connections between two popular and useful tools in theoretical computer science, namely, universal hashing and pairwise independent random variables; and classical combinatorial stuctures such as error-correcting codes, balanced incomplete block designs, difference matrices and orthogonal arrays. more >>>