TypeError: Object type <class 'str'> cannot be passed to C code

Question

I am trying to implement aes encryption and decryption in python. When I execute code, it returns error. I have installed anaconda on my machine. I am running scripts in jupyter notebook.

!pip install pycryptodome

import base64
from Crypto import Random
from Crypto.Cipher import AES

BS = 16
pad = lambda s: s + (BS - len(s) % BS) * chr(BS - len(s) % BS)
unpad = lambda s : s[0:-ord(s[-1])]

class AESCipher:

    def __init__( self, key ):
        self.key = key

    def encrypt( self, raw ):
        raw = pad(raw)
        iv = Random.new().read( AES.block_size )
        cipher = AES.new( self.key, AES.MODE_CBC, iv )
        return base64.b64encode( iv + cipher.encrypt( raw ) )

    def decrypt( self, enc ):
        enc = base64.b64decode(enc)
        iv = enc[:16]
        cipher = AES.new(self.key, AES.MODE_CBC, iv )
        return unpad(cipher.decrypt( enc[16:] ))

cipher = AESCipher('mysecretpassword')
encrypted = cipher.encrypt('Secret')
decrypted = cipher.decrypt(encrypted)
print(encrypted)
print(decrypted)

How to solve this ?

please fix your indentation. what is the error? (which line, etc...) — Attie
– Attie, Commented Sep 4, 2018 at 12:58
raw=pad(raw). TypeError: Object type <class 'str'> cannot be passed to C code — Jozf
– Jozf, Commented Sep 4, 2018 at 13:09
Your code is written for Python2, in Python3 str and bytes are differend objects. You'll have to replace all your strings with bytes (see str.encode). — t.m.adam
– t.m.adam, Commented Sep 4, 2018 at 19:08
I made the following changes to the above code. pwd=b"mysecretpassword" cipher = AESCipher(pwd) msg=b"Secret" encrypted = cipher.encrypt(msg) print(encrypted) print(decrypted) It returns TypeError: can't concat str to bytes — Jozf
– Jozf, Commented Sep 5, 2018 at 4:47

Ahmed Yousif · Accepted Answer · 2018-09-05 07:03:15Z

3

just update unpad to be unpad = lambda s : s[0:-ord(s[-1:])] the main issue that ord() expects string of length one if you try to print value of s[-1] it prints 10 which not one char but s[-1:] printed value is b'\n' which is one char

also encode key to be bytes bytes(key, 'utf-8') and pad

pad = lambda s: bytes(s + (BS - len(s) % BS) * chr(BS - len(s) % BS), 'utf-8')

to make sure all inputs are bytes

from hashlib import sha256
import base64
from Crypto import Random
from Crypto.Cipher import AES

BS = 16
pad = lambda s: bytes(s + (BS - len(s) % BS) * chr(BS - len(s) % BS), 'utf-8')
unpad = lambda s : s[0:-ord(s[-1:])]

class AESCipher:

    def __init__( self, key ):
        self.key = bytes(key, 'utf-8')

    def encrypt( self, raw ):
        raw = pad(raw)
        iv = Random.new().read( AES.block_size )
        cipher = AES.new(self.key, AES.MODE_CBC, iv )
        return base64.b64encode( iv + cipher.encrypt( raw ) )

    def decrypt( self, enc ):
        enc = base64.b64decode(enc)
        iv = enc[:16]
        cipher = AES.new(self.key, AES.MODE_CBC, iv )
        return unpad(cipher.decrypt( enc[16:] )).decode('utf8')

cipher = AESCipher('mysecretpassword')
encrypted = cipher.encrypt('Secret')
decrypted = cipher.decrypt(encrypted)

print(encrypted)
print(decrypted)

edited Sep 5, 2018 at 7:03

answered Sep 4, 2018 at 13:45

Ahmed Yousif

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4 Comments

Jozf Over a year ago

It again returns the same error. TypeError: Object type <class 'str'> cannot be passed to C code

Ahmed Yousif Over a year ago

@Jozf I have updated my answer I think it is working fine now I tried it on jjupyter notebook

Jozf Over a year ago

Thank you. But in the output, there is b before encrypted and decrypted data. Did you see that ? b'6tx+0XpByP2w2cluCcDgYLnx3Zu65vbM8+Db2su4yKg=' b'Secret' How can we remove that ?

Ahmed Yousif Over a year ago

@Jozf just decode the result .decode('utf8') I updated it in answer

Growyn · Accepted Answer · 2020-10-27 00:22:02Z

//First pip install pycryptodome -- (pycrypto is obsolete and gives issues) // pip install pkcs7

from Crypto import Random
from Crypto.Cipher import AES
import base64
from pkcs7 import PKCS7Encoder
from app_settings.views import retrieve_settings # my custom settings

app_secrets = retrieve_settings(file_name='secrets');


def encrypt_data(text_data):
                    #limit to 16 bytes because my encryption key was too long
                    #yours could just be 'abcdefghwhatever' 
    encryption_key = app_secrets['ENCRYPTION_KEY'][:16]; 

    #convert to bytes. same as bytes(encryption_key, 'utf-8')
    encryption_key = str.encode(encryption_key); 
    
    #pad
    encoder = PKCS7Encoder();
    raw = encoder.encode(text_data) # Padding
    iv = Random.new().read(AES.block_size ) #AES.block_size defaults to 16

                                 # no need to set segment_size=BLAH
    cipher = AES.new( encryption_key, AES.MODE_CBC, iv ) 
    encrypted_text = base64.b64encode( iv + cipher.encrypt( str.encode(raw) ) ) 
    return encrypted_text;

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