1. M. Naor and A. Shamir. Visual cryptography,advances in cryptology. Eurocrypt’94 Proceeding LNCS, 950:1–12, 1995.
2. M. Naor and A. Shamir. Visual cryptography ii: Improving the contrast via the cover base. Theory of Cryptography Library,(96-07), 1996.
3. http://users.telenet.be/d.rijmenants/en/visualcrypto.htm