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I want to make a script to decrypt my filess, but when I try to run my script then show me this message , how can I fix it?

Traceback (most recent call last): File "F:\bug_bounty\decrypt.py", line 46, in File "F:\bug_bounty\decrypt.py", line 24, in decrypt File "C:\Python27\lib\site-packages\Crypto\Cipher\blockalgo.py", line 295, in decrypt return self._cipher.decrypt(ciphertext) ValueError: Input strings must be a multiple of 16 in length

from Crypto.Hash import SHA256 from Crypto.Cipher import AES import os import random import sys def decrypt(key, filename): outFile = os.path.join(os.path.dirname(filename), os.path.basename(filename[11:])) chunksize = 64 * 1024 with open(filename, 'rb') as infile: filesize = infile.read(16) IV = infile.read(16) decryptor = AES.new(key, AES.MODE_CBC, IV) with open(outFile, 'wb') as outfile: while True: chunk = infile.read(chunksize) if len(chunk) == 0: break outfile.write(decryptor.decrypt(chunk)) outfile.truncate(int(filesize)) def allfiles(): allFiles = [] for (root, subfiles, files) in os.walk(os.getcwd()): for names in files: allFiles.append(os.path.join(root, names)) return allFiles password = 'M4st3rRul3zs' files = allfiles(); for filename in files: if os.path.basename(filename).startswith("(encrypted)"): print "%s is already encrypted" %filename pass else: decrypt(SHA256.new(password).digest(), filename) print "Done decrypting %s" %filename """os.remove(filename)"""
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4 Answers 4

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Here is the small trick you could use while encrypting the data if your data size is not large.

plaintext = "some text" encryptor = AES.new(key, AES.MODE_CBC, iv) ciphertext = encryptor.encrypt(plaintext*16)

This will ensure that your input data is a multiple of 16. And of course, you would like to get the original data back when decrypting.

cipher = AES.new(key, AES.MODE_CBC, iv) decrypttext = cipher.decrypt(ciphertext) decrypttext = decrypttext[0:len(plaintext)]

Now, decrpyttext has your original plaintext.

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Or, you could also use decrpyttext = decrpyttext[0: len(decrpyttext)//16]
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From Crypto++ wiki.

The block size is determined by AES::BLOCKSIZE. For AES, this is always 16 bytes

AES is a block cipher, it works on 16-byte (128-bit) blocks. It can't work with data smaller or bigger than 16 bytes. Smaller data needs to be padded until they're 16 bytes, and larger data needs to be split into 16-byte blocks.

Also there are algorithms that help you achieve just that (work on data larger than the cipher's block size), they're called block cipher modes of operation.

Have a look at this How to encrypt more than 16 bytes using AES?

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ValueError: Input strings must be a multiple of 16 in length

That is because AES works with blocks of 128 bits (16 chars). You can consider adding padding to fix this.

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in code how should be? filesize = infile.read(16) IV = infile.read(16) decryptor = AES.new(key, AES.MODE_CBC, IV)
@Aron Imperial google 'pkcs7 padding' or 'zero padding' they're both quite easy to implement
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AES works with blocks of 16 chars. This how you can add extra padding

 import random import string 
plaintext = "Encrypt me" encryptor = AES.new(key, AES.MODE_CBC, iv) while len(bytes(plaintext, encoding='utf-8')) % 16 != 0: plaintext = plaintext + random.choice(string.ascii_letters) ciphertext = encryptor.encrypt(plaintext)
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While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply.

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