I am coding a python file encrypter with fernet module;
I want encrypt part of the file bytes for increase the speed of proccess… (Not full of that)
I couldn’t see a problem during this action but the result was not good!
The decrypted file was broken!

Encrypt.py :

from cryptography.fernet import Fernet

motherFuckerCipher = Fernet.generate_key()


with open('myCode.txt','wb') as filekey:
    filekey.write(motherFuckerCipher)


# Encrypt the files such a good boy!

with open("myCode.txt","rb") as mobinsKey:
    mobin = mobinsKey.read()

fernet = Fernet(mobin)

with open("sikish.jpg","rb") as file:
    original = file.read()


# print(original)
selectedStr = original[0:100]
notSelectedStr = original[100:]
# print(notSelectedStr)
encrypted = fernet.encrypt(selectedStr)
# print(encrypted)
lengthOfEncryptedString = len(encrypted)

fullSource = str(lengthOfEncryptedString).encode("utf-8") + b"@@" + encrypted + b"@@" + notSelectedStr


with open("encryptedSikish.jpg","wb") as file:
    file.write(fullSource)

decrypt.py :

from cryptography.fernet import Fernet

with open("encryptedSikish.jpg","rb") as file:
    encrypted = file.read()

with open("myCode.txt","rb") as code:
    mykey = code.read()

fernet = Fernet(mykey)



# print("{} | {}".format(encrypted,mykey))


# Decrypt like mobin from my life!
allString = str(encrypted).split("@@")

print(allString[2])

decrypted = fernet.decrypt(allString[1])



with open("DecryptedSikish.jpg","wb") as finalfile:
    finalfile.write(decrypted + allString[2].encode("utf-8"))

Please help me…
I coded a basic file for check and anylyze the difference between original file and decrypted file, But I don’t know what is problem!

Thanks.