Created
April 16, 2022 19:21
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Q/Create software that can encrypt and decrypt using a 2 * 2 Hill cipher
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| import string | |
| import numpy | |
| from sympy import Matrix | |
| def HillEncrypt(message : string, key: numpy.ndarray): | |
| message = message.replace(" ", "") | |
| if len(message)%2 != 0: | |
| message += 'a' | |
| indexMessageArray = GetIndexArrayFromString(message) | |
| rowNumber = int(len(message)/2) | |
| messageMatrix = numpy.array(indexMessageArray).reshape(rowNumber,2) | |
| resultMatrix = messageMatrix.dot(key) | |
| resultMatrix = resultMatrix%26 | |
| return GetStringFromIndexArray(resultMatrix.flatten()) | |
| def HillDecrypt(cipher : string, key : numpy.ndarray): | |
| cipher = cipher.replace(" ", "") | |
| indexCipherArray = GetIndexArrayFromString(cipher) | |
| rowNumber = int(len(cipher)/2) | |
| cipherMatrix = numpy.array(indexCipherArray).reshape(rowNumber,2) | |
| keyInverse = numpy.array(Matrix(key).inv_mod(26)) | |
| resultMatrix = cipherMatrix.dot(keyInverse) | |
| resultMatrix = resultMatrix%26 | |
| return GetStringFromIndexArray(resultMatrix.flatten()) | |
| def GetIndexArrayFromString(input: string): | |
| lettersIndexedArray = [] | |
| for letter in input: | |
| lettersIndexedArray.append(GetIndexFromLetter(letter)) | |
| return lettersIndexedArray | |
| def GetStringFromIndexArray(leterIndexes : list): | |
| result = "" | |
| for index in leterIndexes : | |
| result += GetLetterFromIndex(int(index)) | |
| return result | |
| def GetIndexFromLetter(letter): | |
| return string.ascii_uppercase.index(letter.upper()) | |
| def GetLetterFromIndex(index): | |
| return string.ascii_uppercase[index] | |
| message = "meet me at eight" | |
| key = numpy.array( | |
| [[9,4], | |
| [5,7]]) | |
| cipher = HillEncrypt(message, key) | |
| decryptedMessage = HillDecrypt(cipher, key) | |
| print(cipher) #print YYBTYYRDYULVPY | |
| print(decryptedMessage) #print MEETMEATEIGHTA |
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