Encode/decode (secret) encrypted data/messages in any binary file using fernet encryption.

main.py

"""
        Usage (Encryption):
        python3 main.py encrypt fileIn.png fileOut.png "Hello World!"
        
        Usage (Decryption):
        python3 main.py decrypt fileIn.png DECRYPTION_KEY
        OR
        python3 main.py decrypt fileIn.png DECRYPTION_KEY --out=fileOut.txt
"""

from os import write
from sys import argv, stdout
from cryptography.fernet import Fernet

indiceSig = b"\x29\x2f\xd1\x2f\xa1\x2f\x28"

# FERNET ENCRYPT
def fencrypt(key, value):
    f = Fernet(key)
    return f.encrypt(value)

# FERNET DECRYPT
def fdecrypt(key, evalue):
    f = Fernet(key)
    return f.decrypt(evalue)

def usage(code=0):
    stdout.write(
        "\r\n\n"\
        "Usage (Encryption): \n"\
        "python3 main.py encrypt fileIn.png fileOut.png \"Hello World!\"\n\n"\
        "Usage (Decryption): \n"\
        "python3 main.py decrypt fileIn.png DECRYPTION_KEY --out=fileOut.txt\n\n"\
        "A script by Aero\r\n\n"
    )   
    exit(0)

# CHECK USAGE TYPE
try:
    if (argv[1].lower() == "encrypt"):
        encrypt = True

    elif (argv[1].lower() == "decrypt"):
        encrypt = False

    else:
        usage()
except:
    usage()


if encrypt:
    
    # GENERATE KEY
    key = Fernet.generate_key().decode()
    
    # GET ARGS
    try:
        fileIn = argv[2]
        fileOut = argv[3]
        message = argv[4]
    except:
        usage()

    # OPEN INPUT FILE & GET CONTENT BUFFER
    with open(fileIn, "rb") as f:
        _in = f.read()

    # OPEN OUTPUT FILE
    with open(fileOut, "wb") as f:
        f.write(
            _in
            + indiceSig
            + fencrypt(key, bytes(message, 'utf-8'))
            + indiceSig
        ) 
    
    stdout.write(
        f"\r\nSuccessfully embedded encrypted message based on {fileIn} to {fileOut}!"\
        f"\nDecryption Key: {key}"
    )


# DECRYPT
else:

    # GET ARGS
    try:
        fileIn = argv[2]
        key = argv[3]
    except:
        usage()

    try:
        fileOut = argv[4].strip("--out=")
    except:
        fileOut = None
    
    # OPEN INPUT FILE
    with open(fileIn, "rb") as f:
        buffer = f.read()
        try:
            message = fdecrypt(key, buffer.split(indiceSig)[1].split(indiceSig)[0]).decode()
        except:
            stdout.write("\r\nInvalid Decryption Key!")    

    # WRITE TO CONSOLE IF OUTPUT FILE NOT SPECIFIED
    if (fileOut is None):
        stdout.write(f"\r\nDecrypted Message!\n\nContent:\n{message}")
    else:
        with open(fileOut, "w+") as f:
            f.write(message)
        stdout.write(f"\r\nDecrypted message written to {fileOut}!")

stdout.write('\r\n\nHave a nice day! :)')