Cipherjack Is A Successful Lawyer Who Runs A Law Firm

Cipherjack Is A Successful Lawyer Who Runs a Law Firm Tha

QUESTION 5 – CIPHER Jack is a successful lawyer who runs a law firm that deals with sensitive cases. In 2017, after the widely known ransomware attacks, their data was compromised. As a protective measure, he requested that all employees must encrypt their messages to each other. Employees generally exchange instructions or case updates with messages that are no longer than thirty characters each. For the purpose of hiding the meaning of the messages, they were told to encrypt them using Caesar cipher substitution then using another substitution where the key is 567.

Once the message is processed through the aforementioned methods, they added an extra layer of security by encrypting the message with One Time Pad that increments by one each time it’s used but remains less or equal to 15 for encryption and decryption. For one particular message between two employees, that key was: 7,15,12,6,8,9,4,2,1,13,12,5,3,1,8,15,6,4,8,12,8,10,9,14,6,11,13,2,4,6. The receiver received the following ciphertext: LC DOMX IZY XVHP XMJQSH AANW FIHABRT.

Paper For Above instruction

The encryption process described involves multiple layers designed to obscure the original message for security purposes. The steps include applying a Caesar cipher, a substitution cipher with a large key, followed by a One Time Pad (OTP) encryption with an incrementing key sequence. Decoding the message requires reversing these steps carefully, starting from the received ciphertext.

First, recognize that the message was encrypted with a combination of methods; thus, decrypting it involves peeling back each layer in reverse order. Since the ciphertext received is: "LC DOMX IZY XVHP XMJQSH AANW FIHABRT," and knowing the final encryption was OTP with incrementing keys, we start by removing that layer.

The OTP process involved a sequence of keys: 7,15,12,6,8,9,4,2,1,13,12,5,3,1,8,15,6,4,8,12,8,10,9,14,6,11,13,2,4,6. Each character in the ciphertext has been shifted forward by the key during OTP encryption. Since the OTP adds the key to the plaintext, we decrypt by subtracting the key from the ciphertext characters, adjusting for the alphabet.

To proceed, we need to convert each ciphertext letter to its corresponding alphabetical index (A=0, B=1, ..., Z=25). Then, subtract the key values listed correspondingly, wrapping around if necessary, to recover the intermediate message. Repeating this process for all characters reconstructs the message at the previous layer.

Following that, we reverse the second substitution cipher with key 567. Since 567 modulo 26 is 567 - 21*26 = 567 - 546 = 21, indicating that the substitution key effectively shifts or substitutes based on a certain pattern. In classic substitution ciphers, a key like 567 could correspond to a shift cipher once reduced modulo 26, which is 21. Therefore, the substitution could be a shift cipher with key 21, requiring us to shift letters backward accordingly.

Finally, the initial Caesar cipher substitution was applied. The Caesar cipher typically involves shifting each letter by a fixed number of positions. Since the description implies a shift, once more, we invert the shift for decryption, applying the reverse shift to retrieve the original message.

By systematically reversing each encryption layer—OTP, substitution, then Caesar cipher—using the provided keys and standard alphabetic conversions, the original message can be reconstructed. This multi-layered encryption protocol ensures the confidentiality of the firm's communications, thwarting unauthorized access or interception.

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