# Encryption and Decryption Text 
#### Video Demo:  <https://www.youtube.com/watch?v=EISF5IKysJU&ab_channel=GabrielD>
#### Description:

This program serves as a comprehensive encryption and decryption tool with eight distinct options. It enables users to encrypt and decrypt text using various methods. Options 1 and 2 implement Caesar cipher encryption and decryption, respectively, requiring user input for text and rotation shift values. Option 3 performs SHA-256 encryption on user-provided text, while Option 4 explains the impossibility of SHA-256 decryption due to its one-way nature. Options 5 and 6 utilize Fernet symmetric encryption, generating a private key and allowing users to encrypt and decrypt text. Options 7 and 8 involve RSA encryption and decryption, generating key pairs, processing user input, and saving encrypted text and private keys to files. Overall, the program provides a user-friendly interface for securing and revealing information through diverse cryptographic techniques.

Import Statements:

These statements play a crucial role in incorporating essential modules and libraries into the code. Notable libraries encompass cryptography for cryptographic operations and Fernet for symmetric encryption.

Global Variables:

PRIVATE_KEY_FILE = "private_key.txt"
ENCRYPTED_FILE = "encrypted_message.txt"

These global variables delineate the file names for storing the private key and encrypted text.

RSA Key Pair Generation:

generate_rsa_key_pair()

This function generates an RSA key pair (private and public keys) and returns them as bytes in PEM format.

RSA Encryption:

rsa_encrypt(text, public_key_bytes)

This function takes plaintext text and a public key in bytes, encrypts the text using RSA-OAEP encryption, and returns the encrypted text.

RSA Decryption:

rsa_decrypt(encrypted_text, private_key_bytes)

This function takes encrypted text and a private key in bytes, decrypts the text using RSA-OAEP decryption, and returns the decrypted text as a string.

SHA-256 Encryption:

sha256_encrypt(text)

This function takes plaintext text, computes its SHA-256 hash, and returns the hash as a hexadecimal string.

Caesar Cipher Encryption:

def caesar_encrypt(text, shift)

This function performs Caesar cipher encryption on plaintext text with a specified shift value.

Caesar Cipher Decryption:

caesar_decrypt()

This function decrypts Caesar cipher encrypted text by applying a negative shift.

Fernet Symmetric Encryption:

encrypt_with_private_key()

This function encrypts plaintext text using Fernet symmetric encryption with a private key and returns the encrypted text.

Fernet Symmetric Decryption:

decrypt_with_private_key()

This function decrypts Fernet symmetric encrypted text using a private key and returns the decrypted text.

RSA Decryption Wrapper:

decrypt_with_rsa_private_key(encrypted_text, private_key)

A wrapper function for decrypting RSA encrypted text, assuming there's an RSA decryption function.

Save Private Key to File:

save_private_key_to_file()

This function saves a private key to a file.

Load Private Key from File:

load_private_key_from_file()

This function loads a private key from a file and prints its content.

Save Encrypted Text to File:

save_encrypted_text_to_file()

This function saves encrypted text to a file.

Main Function:

The main function serves as the script's entry point, presenting an interactive menu for the user to choose encryption or decryption methods. The selected method is then executed.

Print Menu:

print_menu()

This function prints the menu of available encryption and decryption methods.

User Input:

encryption_method = input('Enter an encryption method: ')

This line captures user input for choosing an encryption or decryption method.

Menu Options:

The code employs a series of if and elif statements to check the user's input and execute the corresponding encryption or decryption method based on the chosen option.

Handling Each Option:

• Option 1 (Caesar Encryption): Takes input text and rotation shift value. Calls caesar_encrypt function. Prints original and encrypted text.
• Option 2 (Caesar Decryption): Takes input encrypted text and rotation shift value. Calls caesar_decrypt function. Prints original and decrypted text.
• Option 3 (SHA-256 Encryption): Takes input text. Calls sha256_encrypt function. Prints original and encrypted text.
• Option 4 (SHA-256 Decryption): Prints that SHA-256 decryption is not possible as it's a one-way hash function.
• Option 5 (Fernet AES Encryption): Generates a Fernet private key. Takes input text. Calls encrypt_with_private_key function. Prints private key, original, and encrypted text.
• Option 6 (Fernet AES Decryption): Takes input encrypted text and private key. Calls decrypt_with_private_key function. Prints decrypted text.
• Option 7 (RSA Encryption): Generates RSA key pair. Takes input text. Calls rsa_encrypt function. Prints public key, private key (to be kept safe), and encrypted text. Saves private key and encrypted text to files.
• Option 8 (RSA Decryption): Checks if the private key file exists. Loads private key. Takes input path to the file containing encrypted text. Reads encrypted text from the file. Calls decrypt_with_rsa_private_key function. Prints decrypted text.

Exception Handling:

The try block manages potential exceptions like ValueError and other unexpected errors. If an exception occurs, it prints an error message and exits the program.

This menu-driven approach empowers the user to interactively choose different encryption and decryption methods based on their preferences.