How to decrypt an AES encrypted data with key and iv already provided

Question

I am trying to decrypt an AES encrypted data. I am having the key and iv with me but I think key is also encoded.

Here is the code I have used:

import binascii
from Crypto.Cipher import AES
enckey = '5f35604280b44dd1073f7ee83e346d81'
key = binascii.unhexlify(enckey)
key32 = "{: <32}".format(key).encode("utf-8")
data='692fa1deafad8ad80b98cd6f077899e9be457ac5364c3822aae9457d4912e4829d71cb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'
cipher_text = binascii.unhexlify(data)
# Decryption
decryption_suite = AES.new('key32', AES.MODE_CBC, 'heF9BATUfWuISyO8')
plain_text = decryption_suite.decrypt(cipher_text)
print plain_text

And this is the error I am receiving :

UnicodeDecodeError: 'ascii' codec can't decode byte 0x80 in position 4: 
ordinal not in range(128)

I am unable to figure out the problem with my key and data... And please let me know if I have to make any changes to my code.

Possible duplicate of [Encrypt & Decrypt using PyCrypto AES 256](https://stackoverflow.com/questions/12524994/encrypt-decrypt-using-pycrypto-aes-256) — Alpesh Valaki, Jul 28 '17 at 10:48
There is almost certainly an encoding issue. Please show how the key and IV are encoded/decoded in the language that was used to produce this ciphertext. Otherwise, this is plain guessing. — Artjom B., Jul 28 '17 at 16:48
That's the problem.. I am not provided with the encoding method used here. I am just provided with key, iv and data. — Mayank Raj, Jul 28 '17 at 18:27

score 2 · Answer 1 · answered Jul 29 '17 at 10:35

The following code works:

from Crypto.Cipher import AES

keyAscii = '5f35604280b44dd1073f7ee83e346d81'
keyBinary = bytes(keyAscii, 'ascii')
ciphertextHex='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'
ciphertextBinary = bytes.fromhex(ciphertextHex)
ivAscii = 'heF9BATUfWuISyO8'
ivBinary = bytes(ivAscii, 'ascii')
# Decryption
decrypter = AES.new(keyBinary, AES.MODE_CBC, ivBinary)
plaintextBinary = decrypter.decrypt(ciphertextBinary)
plaintext = plaintextBinary.decode('utf-8')
print(plaintext)

and outputs

connection_type=wifi&android_id=863e87fea9a09533&app_name=AstroNest&app_version=53&app_version_name=2.7.1&device_brand=motorola&device_cpu_type=armv7l&device_model=XT1562&google_aid=ab95a01a-242b-4ac2-ad12-b6189e983a56&google_ad_tracking_disabled=0&insdate=1494826343&installer=com.android.vending&language=en&mac_address=02%3A00%3A00%3A00%3A00%3A00&mat_id=45c0a743-a948-434b-a20d-fe66e870d285&os_version=6.0.1&screen_density=3.0&screen_layout_size=1920x1080&sdk_version=3.11.4&conversion_user_agent=Dalvik%2F2.1.0+%28Linux%3B+U%3B+Android+6.0.1%3B+XT1562+Build%2FMPDS24.107-70-1-5%29&currency_code=USD&revenue=0.0&system_date=1494826532

But it's cryptographically wrong in many ways:

The key looks like 32 character hex string (which would encode a 128-bit key), but you actually need to treat it as ASCII encoding a 32-byte key. That's wrong, since keys are supposed to be uniformly distributed binary string
Similarly an IV is supposed to be a uniform binary, but it's actually ASCII
The IV is fixed, but the whole point of an IV is to be different (unpredictably random for CBC mode) for each message.
CBC mode is vulnerable to padding oracle attacks, which allow an active attacker to recover the plaintext if they can execute a chosen ciphertext attack where they learn which ciphertext decrypt successfully.

You should use authenticated encryption with unique IVs instead.

If I was the the encoder I would have probably known how to decode it. It's work of some dumbhead I guess — Mayank Raj, Jul 29 '17 at 13:32

score 0 · Answer 2 · answered Jul 28 '17 at 11:19

this one may help you

import binascii
from Crypto.Cipher import AES
import re

enckey = '5f35604280b44dd1073f7ee83e346d81'
key32 = "{: <32}".format(enckey).encode("utf-8")
cipher = AES.new(key32, AES.MODE_ECB)
data='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'
cipher_text = binascii.unhexlify(data)
# Decryption


plain_text = re.sub('\0*$','', cipher.decrypt( data[16:]))
print plain_text

or try this

import binascii
from Crypto.Cipher import AES


enckey = '5f35604280b44dd1073f7ee83e346d81'
key32 = "{: <32}".format(enckey).encode("utf-8")
cipher = AES.new(key32, AES.MODE_ECB)
data='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'
cipher_text = binascii.unhexlify(data)
# Decryption


plain_text = cipher.decrypt(cipher_text)
print plain_text

I tried both your codes but they are not able to decrypt the data. It doesn't show any error but the output doesn't makes any sense.. It's just showing weird symbols. This is what used to get without unhexlify but now it's again the same. — Mayank Raj, Jul 28 '17 at 11:51

How to decrypt an AES encrypted data with key and iv already provided

2 Answers2