Conventions in Cryptography
Throughout the site various cryptgraphic conventions will be used, which are explained here.
- The plaintext is the message that is being encrypted by the sender of the message, and will be written in lowercase letters, and surounded by quotation marks.
- The ciphertext is the encrypted message that is actually sent to the recipient to be decrypted, and will be written using uppercase letters, and surounded by quotation marks.
- An intercept is a piece of encrypted text that has been discovered by an interceptor. That is, it is a ciphertext when you do not know the cipher used.
- Most ciphers use a key to make the encryption unique and hence more secure. The key usually takes the form of either a number or a word, and it always changes the more general algorithm for the encryption in some way. By using a key, the sender is trying to make the plaintext irretrievable should the ciphertext fall into the hands of an interceptor who does not know the key, even if they know which cipher has been used. This is at the very heart of cryptography, and is known as Kerckhoffs's Principle (or Shannon's Maxim). The key will always be written in lowercase, and in italics.
- The alphabet used in the encryption process can make a big difference to the ciphertext. It consists of the letters and symbols which will be transformed by the cipher. More importantly, any symbol which is NOT in the alphabet will be left unaltered in the ciphertext. The standard alphabet we shall use is the 26 Roman Letters "abcdefghijklmnopqrstuvwxyz". This means that any spaces, punctuation marks or numbers will not be changed in the ciphertext. Other alphabets can also be used containing these extra characters, and examples will be given for the more simple ciphers using these.