Question

Subject : Cryptography (computer science)

After reading chapter 3, Analyze the history of Caesar Cypher and its impact on cryptography.

The initial post should be at least 400 words.

Answer 1

Caesar Cypher and its impact on cryptography.

The "Caesar Box," or "Caesar Cipher," is one of the earliest known ciphers. Developed around 100 BC, it was used by Julius Caesar to send secret messages to his generals in the field. In the event that one of his messages got intercepted, his opponent could not read them. This obviously gave him a great strategic advantage. So, what was the code? Caesar shifted each letter of his message three letters to the right to produce what could be called the ciphertext. The ciphertext is what the enemy would see instead of the true message. So, for example, if Caesar’s messages were written in the English alphabet, each letter “A” in the message would become a "D," the "B’s" would become "E’s," and the "X's" become "A’s." This type of cipher is appropriately called a “shift cipher.”

Caesar’s magic number was three, however, a modern day use of the Caesar Cipher is a code called "ROT13." ROT13, short for "rotate by 13 places," shifts each letter of the English alphabet 13 spaces. It is often used in online forums to hide information such as movie and tv show spoilers, solutions to puzzles or games, or offensive material. The code is easily crackable, however, it hides the information from the quick glance. Because of the use of a key, the Vigenère Cipher cannot initially be cracked by using a simple frequency analysis like you could do with a Caesar Cipher. Though, the main weakness of a Vigenère Cipher is the repeating of the key. So, in our example, “dog” was repeated twice in order to match the number of letters in the word “attack.” If an attacker guesses the key’s length, it becomes much easier to crack. The ciphertext is then treated like a series of small Caesar Ciphers, and a method such as frequency analysis could then be performed to crack the code.

But how can an attacker guess the length of the key? There are actually two methods: the Kasiski examination and the Friedman test. If the attacker notices that there are repeated segments of text in the ciphertext, a Kasiski examination would be effective in cracking the code. The attacker would count the distance of letters between repeated text to get a good idea of how long the key is. The Friedman test takes an algebraic approach utilizing a formula to measure the unevenness of the cipher letter frequencies to break the cipher.