Assignment 5

Reading assignment 5 was fairly straightforward and brief with regard to its sections, sections 2.5-2.8, but some confusion was elicited by the introduciton of block ciphers. Specifically, while the concept of blocks of text being encrypted together is straightforward, deciphering which are block and which are normal requires some thought. For instance, the enigma cipher encrypts one letter at a time, but if one letter is changed, the order of keys may also change. After awhile, however, these distinctions have become clearer and bear thinking about each time a new cryptosystem is encountered.

Upon reflection, perhaps the most important part of this reading was the simplest part: ciphertext does not have to be just letters or numbers, but can be anything as long as it is related logically to the plaintext and can be decrypted according to some procedure.  This was best evidenced in Sherlock Holmes stick figures which contained messges according to a key that assigned letters to arbitrary figures.  Such ciphers have the advantage of possibly being mistaken for non cipher-text and thus add to the security of the information they are hiding.  Due to Kerchoff's law, however, this factor of cryptography receives little attention.