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
... more >>>