– Example : VigenereCipher, Hill Cipher 21. Homework 2 Submit solution to problem 2.18. Even though it is a type of classical and historical cryptography method, it has a special place in my heart because of strong math background and easy adaptation. HILL CIPHER .The multiletter cipher hill cipher developed by the mathematician Lester hill in 1929. . Write your keyword across the top of the text you want to encipher, repeating it as many times as necessary. View Caesar Cipher PPTs online, safely and virus-free! Hill's cipher machine, from figure 4 of the patent. The algorithm m plaintext letter substitution cipher text m ,numerical value(a=0,b=1,….z=25) c1=(k11p1+k12p2+k13p3)mod 26 c2=(k21p1+k22p2+k23p3)mod 26 c3=(k31p1+k32p2+k33p3)mod 26 the column of vectors: c1 k11 k12 k13 p1 c2 k21 k22 k23 p2 mod 26 c3 k31 k32 k33 p3 12. Remember that calculating m e mod n is easy, but calculating the inverse c-e mod n is very difficult, well, for large n's anyway. • Example – substitution cipher • Consider a block cipher: blocks of size b bits, and key of size k • The number of all possible functions mapping b bits to b bits is (2b)2b Necessary Condition (cont.) Get ideas for your own presentations. 16 Conclusion The Hill 2-cipher is a great example of how mathematics can change the way we communicate. In classical cryptography, the Hill cipher is a polygraphic substitution cipher based on linear algebra.Invented by Lester S. Hill in 1929, it was the first polygraphic cipher in which it was practical (though barely) to operate on more than three symbols at once.. If we would do a Hill 3-cipher, we would group the letters in groups of 3 letters and use a 3 x 3 transformation matrix, but in this example we're using a Hill 2-cipher. Chosen plaintext – The cryptanalysts gains temporary access to the encryption machine. • Keyless Cipher – a cipher that does not require the use of a key • key cannot be changed If the encryption algorithm should fall into the interceptor ’s hands, future messages can still be kept secret because the interceptor will not know the key value. The first L is encrypted as N; the second as Z. If multiplication is used to convert to cipher text, it is called a wrap-around situation. The key table is a 5×5 grid of alphabets that acts as the key for encrypting the plaintext. Cipher text only – A copy of cipher text alone is known to the cryptanalyst. Hill ciphers are quite simple, while other methods are much more sophisticated, like RSA public key encryption that involves two very large prime numbers and is used for internet security. Many are downloadable. In this example, the letter e in the plaintext is variably encrypted to S and V, and in the ciphertext W is, in different places, the result of a plaintext f, t, and r. This variability makes attacking the ciphertext by the frequency of letters in English much more difficult. Hill devised a mechanical encryption machine to help with the mathematics; his machine relied on gears and levers, but never gained widespread use. I need to encrypt a file (such as .doc, .ppt, .jpeg, etc), and not just the contents of file. Consider the letters and the associated numbers to be used as shown below − The numbers will be used for multiplication procedure Hill Cipher. When it was first put to the British Foreign Office as a cipher, it was rejected due to its perceived complexity. In cases where bits of plaintext is shorter than the block size, padding schemes are called into play. Let's say we want to encipher the following sentence,"THE PROFESSOR IS EVIL", into ciphertext. In order to encipher by Vigenère cipher, you need two things: a keyword and the Vigenère square, below. 2.18. Pick a keyword (for our example, the keyword will be "MEC"). •In a decimation cipher A always represents itself 2-18 Washington University in St. Louis CSE571S ©2011 Raj Jain. Actually, it was the first one appearing in the history. The next two examples, playfair and Vigenere Cipher are polyalphabetic ciphers. View L2.ppt from CSE 402 at JK Lakshmipat University. The Hill cipher algorithm is one of the symmetric key algorithms that have several advantages in data encryption. Encryption Abjat and this letter serves as a conversion of plaintext (messages or data) and key that you want to encrypt and decrypt. – Hill Cipher – Cryptography is the art of protecting information by transforming it into a format that is not directly readable, called cipher text. A = 0, B= 1….z = 25; Organize the plain text message as a matrix of numbers base on the above step that is in number format. 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