Encrypt data with accents using python crypto library

Question

I am implementing DES3 in Python using Crypto library. I was doing some test when I've stumbled upon the next problem:

If the plain text that I want to encrypt contains strange charactes, as accents, fails.

For example, my code is working fine when I try to encrypt the next word:

Text to be encrypted(multiple of 8 in length) : "Hello Jose "

However, it fails if I try to encrypt the same text but containing an accent: Text to be encrypted (multiple of 8 in length)= "Hello José "

The error that I am getting is “ValueError: Input strings must be a multiple of 8 in length”.

If I check the length of the word, it is a multiple of 8.

plaintext="Hello Jose      "
print(" Plain text:" + plaintext)
print(" Plain Text length:" + str(len(plaintext)))

Result: Plain Text length : 16

Find next a reduced example of my code:

from Crypto.Cipher import DES3
import binascii
import base64

plaintext="Hello Jose      "
print(" Plain text:" + plaintext)
print(" Plain Text length:" + str(len(plaintext)))

#### ENCRYPTION 
key ='173JKL3D93A9CNI1G6NP9A14'
key=bytes(key, 'utf-8')
plaintext_bytes=bytes(plaintext, 'utf-8')
print(" Plain Text length:" + str(len(plaintext_bytes)))


cipher_encrypt=DES3.new(key)
encrypted_text=cipher_encrypt.encrypt(plaintext_bytes)
print( " Encrypted word:" + str(encrypted_text))

#### DECRYPTION
cipher_encrypt=DES3.new(key)
decrypted_text=cipher_encrypt.decrypt(encrypted_text)
print(" Decripted text:" + str(decrypted_text,'utf-8') + "\n")

Can anyone help me to understand why it is not working correctly?

Answer 1

Goyo is right. The algorithm reads the plain text as a byte-string. Knowing that, the length in bytes of one character with accent is 2. See next example:

>> a='a'
>> print("length:" + str(len(a.encode('utf-8'))))
length:1

>> a='á'
>> print("length:" + str(len(a.encode('utf-8'))))
length:2

So, firstly you have to encode the text to bytes and then calculate the length.

What you could do is calculate the next multiple of 8 and that should be the length of the plain text. After that, you could fill out the string with whitespace to that length.