Question

4. Given the following code for AES Electronic Code Block implementation for the encryption functionality. Modify the code to create a function named ‘decryptECB(key, ciphertext)’ that accepts key and ciphertext and returns a plaintext.

from base64 import b64decode

from Crypto.Cipher import AES

from Crypto.Util.Padding import pad

from Crypto.Util.Padding import unpad

# We assume that the password was securely shared beforehand

password = input ("Enter the password to decrypt the message: ")

key= pad(password.encode(), 16)

ciphertext = input ("Paste the cipher text here: ")

try:

ct = b64decode(ciphertext)

cipher = AES.new(key, AES.MODE_ECB)

pt = unpad(cipher.decrypt(ct), AES.block_size)

print("The decrypted message was: ", pt)

except ValueError:

print("Incorrect decryption")

Answer 1

# Please install 'pycryptodome' before running this script by using the below command
# pip install pycryptodome

from Crypto.Util.Padding import pad, unpad
from Crypto.Cipher import AES


def encryptECB(_key, _msg):
    cipher = AES.new(_key, AES.MODE_ECB)
    ct = cipher.encrypt(_msg)
    return ct


def decryptECB(_key, _ciphertext):
    decipher = AES.new(_key, AES.MODE_ECB)
    pt = decipher.decrypt(_ciphertext)
    pt = unpad(pt, 16)
    return pt


password = input("Enter the password to decrypt the message: ")
key = pad(password.encode('utf8'), 16)

msg = input("Paste the Message here: ")
msg = pad(msg.encode('utf8'), 16)
try:
    # encrypting message
    ciphertext = encryptECB(key, msg)

    # decrypting message
    plaintext = decryptECB(key, ciphertext)

    # print decrypted message
    print(plaintext)

except ValueError:
    print("Incorrect decryption")