AdditiveCipher

AdditiveCipher#

The AdditiveCipher class implements the Additive Cipher, a type of monoalphabetic substitution cipher that shifts each character by a addding with a specified integer key.

class AdditiveCipher(key: int)#

Creates a new AdditiveCipher instance with the specified key.

Parameters:

key (int) – The integer by which each letter in the plaintext is shifted. Valid values are between 0 and 25.

Attention

AdditiveCipher is a basic symmetric cipher, which should be used ONLY for educational purposes, and NOT in production. Proceed accordingly.

Introduction#

The Additive Cipher (also known as the Caesar Cipher) is one of the oldest known encryption techniques. Each character in the plaintext is shifted by a fixed number of positions based on a given key. Although easy to implement, this cipher is insecure for practical use since it is easily broken by frequency analysis.

Mathematical Details#

In the Additive Cipher:

  • Each letter in the alphabet is mapped to a numeric value.

  • The encryption formula is:
    \[c = (p + k) \mod 26\]
    where:

    • \(c\) is the ciphertext letter,

    • \(p\) is the plaintext letter,

    • \(k\) is the key (shift amount).

  • Decryption reverses this shift with the formula:
    \[p = (c - k) \mod 26\]

Usage#

# Example usage of Additive Cipher to encrypt and decrypt a message
from cryptosystems import AdditiveCipher
cipher = AdditiveCipher(3)
ciphertext = cipher.encrypt("Hello World")
print(ciphertext) # 'Khosk Zruog'
plaintext = cipher.decrypt(ciphertext)
print(plaintext) # 'Hello World'

Methods#

encrypt(plaintext: str) → str#

Encrypts the plaintext using the Additive Cipher.

Parameters:

plaintext (str) – The text to be encrypted.

Returns:

The encrypted ciphertext.

Return type:

str

decrypt(ciphertext: str) → str#

Decrypts the ciphertext using the Additive Cipher.

Parameters:

ciphertext (str) – The text to be decrypted.

Returns:

The decrypted plaintext.

Return type:

str

Notes#

  • Limitations: The Additive Cipher operates on the letters of the alphabet. It does not encrypt spaces, punctuation, or numbers. The key must be an integer between 0 and 25.

  • Security: The Additive Cipher is not secure for practical. The Additive Cipher is vulnerable to frequency analysis, making it unsuitable for secure communications.

  • Application: Suitable for educational purposes or very basic encoding.