It is possible to cryptanalyze simple substitution ciphers (both monoand polyalphabetic) by using a fast algorithm based on a process where an initial key guess is refined through a number of iterations. In each step the plaintext corresponding to the current key is evaluated and the result used as a measure of how close we are in having discovered the correct key. It turns out that only knowledge of the digram distribution of the ciphertext and the expected digram distribution of the plaintext is necessary to solve the cipher. The algorithm needs to compute the distribution matrix only once and subsequent plaintext evaluation is done by manipulating this matrix only, and not by decrypting the ciphertext and reparsing the resulting plaintext in every iteration. The paper explains the algorithm and it shows some of the results obtained with an implementation in Pascal. A generalized version of the algorithm can be used for attacking other simple ciphers as well. Keywords: Cryptanalysis,...

The inclusion-exclusion principle is a combinatorial method for determining the cardinality of a set where each element X 2 U satisfies a list of properties u 1 ; u 2 ; : : : ; u n . In this paper we will display the usefulness of the inclusion-exclusion principle by solving 8 problems of interest to cryptography. These problems will concentrate on the enumeration of boolean functions and permutations that have properties which are considered to be necessary for a cryptographic mapping to be secure. In particular we will be concerned with the properties of nonlinearity and nondegeneracy as these properties correspond to Shannon's notions of confusion and diffusion, respectively. Keywords: probability, enumeration, inclusion-exclusion principle, boolean functions, permutations. 1 Introduction In cryptography we are often interested in determining the probability that a certain event may occur. For example, what is the probability that a given block C of ciphertext is encoded using a...

This paper deals with the tidings of cryptography in history, how it has played a vital role in World War-1, World War-2. It also deals with the Substitution, Transposition Cryptographic techniques and Steganography principles which can be used to maintain the confidentiality of computerized and none computerized information files. A number of well known techniques have been adapted for computer usage including the Ceaser cipher, Mono alphabetic cipher, Homophonic substitution, Bale cipher, Play fair cipher, Poly alphabetic cipher, Vigenere Cipher, One- time pad cipher, Vernam ciphers, Play Color Cipher and usage of rotor machine in Substitutions, Rail fence technique, more complex permutations for more secure transposition and some Steganography principle were briefly discussed with merits and demerits. Finally it gives the broad knowledge on almost all the cryptographic and Steganography principles where a reader or scholar have lot of scope for updating or invention of more secure algorithms to fulfill the global needs in information security.