In cryptography, a Caesar cipher, also known as Caesar’s cipher, the shift cipher, Caesar’s code or Caesar shift, is one of the simplest and
most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some
fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The
method is named after Julius Caesar, who used it in his private correspondence. The encryption step performed by a Caesar cipher is often
incorporated as part of more complex schemes, such as the Vigenère cipher, and still has modern application. As with all single alphabet
substitution ciphers, the Caesar cipher is easily broken and in modern practice offers essentially no communication security. Generally
speaking, it is a great exercise to understand crypto, and for our purposes, it deals with various concepts for learning a new programming
language. The Caesar Cipher, the Multiplication Cipher and the Linear Cipher have one property in common. They all fall in the category of
Monoalphabetic Ciphers: “Same plain letters are encoded to the same cipher letter.” I.e. in the Caesar Cipher each “a” turned into “d”, each “b”
turned into “e”, etc. The following holds true for each of the above Ciphers: Although letters are changed the underlying letter frequencies are
not! If the plain letter “a” occurs 10 times its cipher letter will do so 10 times. Therefore, ANY Monoalphabetic Cipher can be broken with the
aid of letter frequency analysis. To compute the relative frequencies of each letter in a cipher text simply count the occurrences of the letter
in the text. Afterwards compare the letter frequencies with those of the English language (assuming that the cipher text stems from an English
plain text). You must use the following fact in your solution (A brute force attack would get a zero grade – be careful): a) The most frequent
letter of the English language is “e” (with about 12%) followed by t,i,o,a,n,s,r which is very helpful to break thecipher text. b) The longer
the cipher text the better do the counted letter frequencies converge to the actual English plain letterfrequencies.
We received the following ciphertext which was encoded with a shift cipher: xultpaajcxitltlxaarpjhtiwtgxktghidhipxciwtvgtpilpitghlxiwiwtxgqadds
1. Perform an attack (no brute force) against the cipher based on a letter frequency count: How many letters do you have to identify through a
frequency count to recover the key? What is the cleartext? 2. Who wrote this message? – Hint: Please print the occurrences of each letter and
then the different plaintext outputs based on different keys. Try to do it with the frequencies – it will work in this case.
Question 2 (20 Points) Write YOUR OWN binary to decimal converter and decimal to binary converter including the decimal portion. You can use
console for input. You must use functions. It must be yours – copying code will get 0 credit and will be considered an act of plagiarism. It is
better not to submit.
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