6. Caesar Shift Cipher



The Caesar shift cipher, named because it was used by Julius Caesar himself, is actually 26 different ciphers, one for each letter of the alphabet. ROT1 is just one of these ciphers. A person only needs to be told which Caesar cipher was used in order to decipher a message. If the G cipher is used, then A becomes G, B becomes H, C becomes I, and so on through the alphabet. If the Y cipher is used, then A becomes Y, B becomes Z, C becomes A, and so on. This cipher is the basis for many more complex ciphers, but on its own does not allow great protection of a secret message, as checking 26 different cipher keys does not take a relatively great amount of time. Li bra ghflskhu wklv dqg bra nqrz lw, fods brxu kdqgv.




5. Monoalphabetic Substitution


ROT1, Caesar shift, and Morse code are all of the same type: mono alphabetic substitution, meaning that each letter of the alphabet is replaced according to the key with another letter or symbol. Without knowing the key, these are actually easy to decipher. The most common letter in English is well-known to be E. Therefore, in any mono alphabetic cipher, the most common letter or symbol will also be E. The second most common English letter is T, and the third most common is A, and so these two letters can also be determined. From this point, a person deciphering a message can continue using the frequencies of English letters or they can look for nearly-complete words, such as “T_E” which is most likely “THE.” Unfortunately, this only works for long messages, and not on ones with only a few words, since they do not have enough letters to show which are the most frequent. Mary Queen of Scots famously used a mono alphabetic cipher with several variations that was incredibly difficult, however when it was finally broken, the messages therein gave the evidence needed by her enemies to sentence her to death. Ptbndcb ymdptmq bnw yew, bnwzw raw rkbcriie wrze bd owktxnwa.