How do you decrypt in Hill cipher?

How do you decrypt in Hill cipher?

Decryption. Decrypting with the Hill cipher is built on the following operation: D(K, C) = (K-1 *C) mod 26 Where K is our key matrix and C is the ciphertext in vector form. Matrix multiplying the inverse of the key matrix with the ciphertext produces the decrypted plaintext.

How do you find the key matrix of a 2×2 Hill cipher?

2×2 matrix is just the product down the upper left to lower right diagonal minus the product down the upper right to lower left diagonal.

How is Hill cipher calculated?

Hill cipher is a polygraphic substitution cipher based on linear algebra. Each letter is represented by a number modulo 26. To encrypt a message, each block of n letters (considered as an n-component vector) is multiplied by an invertible n × n matrix, against modulus 26. …

How do you find the K inverse of a hill cipher?

You must study the Linear congruence theorem and the extended GCD algorithm, which belong to Number Theory, in order to understand the maths behind modulo arithmetic. The inverse of matrix K for example is (1/det(K)) * adjoint(K), where det(K) <> 0.

What is polygraphic substitution cipher?

Polygraphic substitution is a cipher in which a uniform substitution is performed on blocks of letters. When the length of the block is specifically known, more precise terms are used: for instance, a cipher in which pairs of letters are substituted is bigraphic.

How do you find the K inverse of a Hill cipher?

How does the Porta cipher work?

Porta encryption uses a key and 11 reversible alphabets each associated with 2 letters of the alphabet: A and B for the first, C and D for the second, and so on. To use the Latin alphabet, the principle has been intrapolated to 26 letters and 13 alphabets. Example: DCODE is then encrypted WVJUR .

Why is Hill cipher used?

Hill Cipher is the application of modulo arithmetic to cryptography. This cryptographic technique uses a square matrix as the key used to encrypt and decrypt [5]. Security is expected to be guaranteed after applying the Hill Cipher algorithm in the process of sending and receiving data.

How do I make my hill cipher more secure?

Saeednia introduced a new way to make Hill Cipher more secure [6] . He suggested to secure the cipher by adding the feature of random permutation of columns and rows of the key matrix, however, it is proved that its vulnerable to known-plaintext as well. …

How do you find the decryption matrix Hill cipher?

To decrypt hill ciphertext, compute the matrix inverse modulo 26 (where 26 is the alphabet length), requiring the matrix to be invertible. Decryption consists in encrypting the ciphertext with the inverse matrix. Note that not all matrices can be adapted to hill cipher.

What will be the ciphered text if the plain text san is?

9. What will be the size of a key matrix if the plain text is “SECRET”? Explanation: Hill cipher uses a n x n matrix in order to cipher the plain text. In this case n=6 so a 6×6 matrix will be used.

How to decrypt a ciphertext encrypted with the Hill cipher?

To decrypt a ciphertext encoded using the Hill Cipher, we must find the inverse matrix. Once we have the inverse matrix, the process is the same as encrypting.

How to find the key matrix of a 2×2 Hill cipher?

– Mathematics Stack Exchange How to find the key matrix of a 2×2 Hill Cipher? In the english language, the most common digraph is TH which is then followed by HE. In this particular example let’s say the digraphs with the most frequencies are RH and NI.

What type of cipher is a digraph cipher?

Unlike the others though it is extendable to work on different sized blocks of letters. So, technically it is a polygraphic substitution cipher, as it can work on digraphs, trigraphs (3 letter blocks) or theoretically any sized blocks.

How do you decrypt a message using a matrix?

To decrypt the message, each block is multiplied by the inverse of the matrix used for encryption. The matrix used for encryption is the cipher key, and it should be chosen randomly from the set of invertible n × n matrices (modulo 26).