ciphers.hill_cipher

Hill Cipher: The ‘HillCipher’ class below implements the Hill Cipher algorithm which uses modern linear algebra techniques to encode and decode text using an encryption key matrix.

Algorithm: Let the order of the encryption key be N (as it is a square matrix). Your text is divided into batches of length N and converted to numerical vectors by a simple mapping starting with A=0 and so on.

The key is then multiplied with the newly created batch vector to obtain the encoded vector. After each multiplication modular 36 calculations are performed on the vectors so as to bring the numbers between 0 and 36 and then mapped with their corresponding alphanumerics.

While decrypting, the decrypting key is found which is the inverse of the encrypting key modular 36. The same process is repeated for decrypting to get the original message back.

Constraints: The determinant of the encryption key matrix must be relatively prime w.r.t 36.

Note: This implementation only considers alphanumerics in the text. If the length of the text to be encrypted is not a multiple of the break key(the length of one batch of letters), the last character of the text is added to the text until the length of the text reaches a multiple of the break_key. So the text after decrypting might be a little different than the original text.

References: https://apprendre-en-ligne.net/crypto/hill/Hillciph.pdf https://www.youtube.com/watch?v=kfmNeskzs2o https://www.youtube.com/watch?v=4RhLNDqcjpA

Classes

HillCipher

Functions

main(→ None)

Module Contents

class ciphers.hill_cipher.HillCipher(encrypt_key: numpy.ndarray)

check_determinant() → None

>>> hill_cipher = HillCipher(np.array([[2, 5], [1, 6]]))
>>> hill_cipher.check_determinant()

decrypt(text: str) → str

>>> hill_cipher = HillCipher(np.array([[2, 5], [1, 6]]))
>>> hill_cipher.decrypt('WHXYJOLM9C6XT085LL')
'TESTINGHILLCIPHERR'
>>> hill_cipher.decrypt('85FF00')
'HELLOO'

encrypt(text: str) → str

>>> hill_cipher = HillCipher(np.array([[2, 5], [1, 6]]))
>>> hill_cipher.encrypt('testing hill cipher')
'WHXYJOLM9C6XT085LL'
>>> hill_cipher.encrypt('hello')
'85FF00'

make_decrypt_key() → numpy.ndarray

>>> hill_cipher = HillCipher(np.array([[2, 5], [1, 6]]))
>>> hill_cipher.make_decrypt_key()
array([[ 6, 25],
       [ 5, 26]])

process_text(text: str) → str

>>> hill_cipher = HillCipher(np.array([[2, 5], [1, 6]]))
>>> hill_cipher.process_text('Testing Hill Cipher')
'TESTINGHILLCIPHERR'
>>> hill_cipher.process_text('hello')
'HELLOO'

replace_digits(num: int) → str

>>> hill_cipher = HillCipher(np.array([[2, 5], [1, 6]]))
>>> hill_cipher.replace_digits(19)
'T'
>>> hill_cipher.replace_digits(26)
'0'

replace_letters(letter: str) → int

>>> hill_cipher = HillCipher(np.array([[2, 5], [1, 6]]))
>>> hill_cipher.replace_letters('T')
19
>>> hill_cipher.replace_letters('0')
26

break_key

encrypt_key

key_string = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'

modulus

to_int

ciphers.hill_cipher.main() → None