Abstract
The security of block and product ciphers is considered using a set theoretic estimation (STE) approach to decryption. Known-ciphertext attacks are studied using permutation (P) and substitution (S) keys. The blocks are formed from two (2) alphabetic characters (meta-characters) where the applications of P and S upon the ASCII byte representation of each of the two characters are allowed to cross byte boundaries. The application of STE forgoes the need to employ chosen-plaintext or known-plaintext attacks.
Highlights
Cryptanalysis is the study of decryption techniques of encrypted information, which involves determining the secret key to the encryption
The second cipher is applied to the ciphertext that results from applying the first cipher to the plaintext
Since Shannon introduced the concept of increasing security by compounding ciphers, it has generally been accepted that product ciphers of the form PSP [1, 3, 4] are more secure than a cipher employing only a permutation (See Fig. 1) or a substitution cipher
Summary
Cryptanalysis is the study of decryption techniques of encrypted information, which involves determining the secret key to the encryption. The process of decryption is a set of iterative applications of a priori knowledge applied to a noisy input in an effort to recover the message from the noise. C = E (M, k), where C is the cipher text and E (M, k) is the encryption function using a key, k, as a noise generator for the message M. The block and product ciphers apply multiple keys to the same data, one after the other. We apply a rule-based set theoretic estimation (STE) [2] approach to capture the properties of m-grams that are derived from a stylistic use of the English language. Results of STE applied to a block P and block S decryption algorithm is presented
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