Informatica

This paper proposes a new family of 4-dimensional chaotic cat maps. This family is then used in the design of a novel block-based image encryption scheme. This scheme is composed of two independent phases, a robust light shuffling phase and a masking phase which operate on image-blocks. It utilizes measures of central tendency to mix blocks of the image at hand to enhance security against a number of cryptanalytic attacks. The mixing is designed so that while encryption is highly sensitive to the secret key and the input image, decryption is robust against noise and cropping of the cipher-image. Empirical results show high performance of the suggested scheme and its robustness against well-known cryptanalytic attacks. Furthermore, comparisons with existing image encryption methods are presented which demonstrate the superiority of the proposed scheme.

After Morris and Thompson wrote the first paper on password security in 1979, strict password policies have been enforced to make sure users follow the rules on passwords. Many such policies require users to select and use a system-generated password. The objective of this paper is to analyse the effectiveness of strict password management policies with respect to how users remember system-generated passwords of different textual types – plaintext strings, passphrases, and hybrid graphical-textual PsychoPass passwords. In an experiment, participants were assigned a random string, passphrase, and PsychoPass passwords and had to memorize them. Surprisingly, no one has remembered either the random string or the passphrase, whereas only 10% of the participants remembered their PsychoPass password. The policies where administrators let systems assign passwords to users are not appropriate. Although PsychoPass passwords are easier to remember, the recall rate of any system-assigned password is below the acceptable level. The findings of this study explain that system-assigned strong passwords are inappropriate and put unacceptable memory burden on users.