Easy Encryption Ciphers Essay, Research Paper

Many messages need to be kept secret, for few people s eyes only and that is why cryptology was invented. In the world of cryptology, there are many different strategies of enciphering or encoding message. Enciphering is a way of substituting letters or numbers in the place of components that make up words. There are many ways to encipher messages, though some are not always the best ways to hide secret messages. In the following, I will discuss the methods of encoding and decoding certain ciphers, as well as how hard they are to break.

The first method of cipher to discuss is called Caesar cipher or additive cipher. In this technique of encryption, the alphabet slides either to the right or left, so that each letter is replaced by another letter that represents it throughout the message, keeping the alphabet in consecutive order. For example, if a is shifted three positions to the left, represented as X , then Y would stand for b. This means that there are twenty-six different ciphers of this system, one for each letter.

The best way of encoding a Caser cipher is to make a key. First, write the alphabet once in lower case. Then match up the shift to its desired position on the alphabet, writing the cipher alphabet in capital letters underneath it. The lower case letters are called the plaintext or cleartext, while the upper case ones are referred to as ciphertext. Using this key, you can now encode your message by looking at the letters of the message in the plaintext and matching them up with the ciphertext below. As the process is repeated, the message appears to start looking like nonsense, when in actuality, it means something. When all letters have been converted into the ciphertext form, the deed is done and the message has been enciphered.

Breaking this kind of cipher is also relatively easy since there are only twenty-six different variables of the ciphers. There are methods, however, that can make it much simpler. For instance, certain letters of the alphabet tend to appear more often in the English language. The letter e is by far the most common, while t is the second. So, by taking tally of how many times the ciphertext letters appear in a secret message, one can often figure out which letter is the e. The frequency of pairs of letters together can also be utilized. The letters he are the most common, often forming the words he, she, and the. If two ciphertext letters tend to turn up in the same order a lot, then it is probable that these two letters make the he duo. However, these conclusions can often be wrong. There is no rule saying that e and he have to exist in a message. And, frequently, when the message is short, neither of these do appear. So, since there are relatively few different ciphers of this method of cipher, it cannot hurt to try each one until one find the right offset to break the code. Also, one can try to count all the characters in the message, making a letter to frequency ratio. When there are ciphertext letters with low frequencies all in a row, that is often a pointer to the letters v, w, x, y, and z. The letters r, s, and t also can be found in a similar way, by finding three letters in consecutive order with high frequencies.

Once the code is broken, one can decode the message. This is done by simply making a key. However, this key will be made to fit the offset or shift of the ciphertext. With the plaintext alphabet on top and the ciphertext alphabet on the bottom, each ciphertext letter can be coordinated with its truly intended character. Once all of the encoded characters are decoded, the process is done and the receiver can read it.

The second technique of cipher to be examined is monoalphabetic cipher. They are very similar to Caesar ciphers, with the exception that there are not shifts in the alphabets. A cipher is called monoalphabetic if any letter of the alphabet is always enciphered by the same ciphertext letter. The ciphertext consists of letters randomly paired up with the plaintext to form the code. With so many new possibilities open, this cipher is much harder to break, yet it is not impossible. There are 4(10^26) different ways of encoding messages in this approach. However, security still remains low when it comes to this form of secret code.

When encoding this type, one makes, as always, a key with the plaintext on top and the ciphertext on bottom. The letters can then be transferred into the gibberish by referring from the plaintext to the ciphertext. Decoding it is just the opposite, by looking at the ciphertext and transforming it into real words. These parts of the work are almost effortless. It is the breaking that is a little bit more difficult.

The breaking of monoalphabetic codes use the same strategies as Caesar ciphers. Frequencies of individual letters are used to figure out which letter is which. Once you find out what e is, you can often guess where other letters go by trial and error. Decoding and breaking are essentially synchronized in this system, since one must use portions of words to figure out others. Monoalphabetic ciphers are more difficult than Caesars, but still are relatively easy.

Next on the list to understand are key phrase ciphers. These are formulated through two components: a key letter and a key phrase. The latter can be any word, but repeat letters int he word are taken out. The reason behind this is that different letters in the plaintext alphabet would end up being the same, and other letters would not exist in the alphabet. For example, with the key word apple, the ciphertext keyword would end up being aple, having each letter represented only once. Aple can then go on to be inserted into the ciphertext alphabet at its position below the key letter in the cleartext. The rest of the letters of the alphabet are placed after the key word in their regular order, omitting the letters of the keyword. Since there is no way to tell how many different keywords there are out there, there is no way to give a number on how many keyword ciphers there are. However, there are less keyword ciphers out there than monoalphabetics, because not all letters in random order can make a keyword.

In order to encode a message one must follow the steps above and then match up the plaintext with the ciphertext, again, making a mass of letters that do not make sense. To break and decode, the same methods used on monoalphabetics can be used on keyword ciphers, as well. That comprises searching for the most frequent or non-frequent characters and pairs. When something repeated comes up, trial and error comes into play. Often, one can use the frequency or non-frequency of consecutive alphabetic characters to break the code, too. But, keep in mind this is not very reliable.

Last of all to talk about is a cipher called affine. It can be understood as a method using numbers to compute the code. Affine ciphers consist of both additive and multiplicative cipher qualities. The first step in the process of constructing an alphabet for affine ciphers is to translate an additive cipher into numbers. For example, the letter a is equal to one, b to two, c to three, et cetera, all the way up to twenty-five which is y ( z equals zero). When a shift of three is added to x , 24 + 3, the result is twenty-seven. Since the alphabet only has twenty-six letters we need to use modulo 26, meaning 27 / 26 has a remainder of one. In mod 26, the remainder is always what one is looking for. One corresponds to the letter a. So, in a shift of three x is one or a. It was mentioned earlier that there are twenty six different forms of additive ciphers, so keep that in mind for when the variables of affine ciphers are calculated.

In a multiplicative cipher a person would use the letter t to represent a number. Let s say t is two. Next, the number which corresponds to the letter, such as one for a, is multiplied by t. So, one times two equals two. Again, one must use mod 26. When two is divided by twenty 26, the remainder is two. A corresponds to b. However, when the whole alphabet is computed into ciphertext, there are some repeats. Two is not a valid number for t as a multiplicative cipher. The only valid ones turn out to be 1, 3, 5, 7, 9, 11, 15, 17, 19, 21, 23, and 25. Hence, there are twelve different multiplicative ciphers.

Combining these two techniques together one composes the affine cipher. The formula is c = t (p + s) mod 26. Meaning the cleartext letter is added to the offset, then a number t is multiplied by it. The result is then divided by 26 and the remainder can be translated into an alphabetic letter. This is how the whole alphabet is encoded. So, gathering the different numbers of ciphers of each that make up affine ciphers, one finds that there are 312 different codes of this method by multiplying the twenty-six additive codes times the twelve multiplicative ones. That is more than Caesar, so obviously it s more complicated to break.

Breaking the code of an affine cipher involves using the the same techniques as the previous codes. Frequency helps to break down the cipher text into the un-coded message. Basically that is all you can do because it s a mono-alphabetic code.

As seen, all of these codes are relatively easy to encipher, break and decipher. Security, in codes like these, does not exist. Someone out there can always figure them out. If a message sent in cipher should be kept secret, I suggest that a much more complicated method be used.