Decrypting secret hex output from AES CTR example in 3rd party application (python)

RE: Decrypting secret hex output from AES CTR example in 3rd party application (python)

Prantae — Fri, 01 Apr 2022 10:23:58 GMT

Thanks Charlie I managed to resolve the problem with the key you hinted.

for any this is my code.

import binascii
import os
from Crypto.Cipher import AES
from Crypto.Util import Counter
def int_of_string(s):
    return int(binascii.hexlify(s), 16)
def encrypt_message(key, plaintext):
    iv = os.urandom(16)
    ctr = Counter.new(128, initial_value=int_of_string(iv))
    aes = AES.new(key, AES.MODE_CTR, counter=ctr)
    return iv + aes.encrypt(plaintext)
def decrypt_message(key, ciphertext):
    iv = ciphertext[:16]
    print(iv)
    ctr = Counter.new(128, initial_value=int_of_string(iv))
    aes = AES.new(key, AES.MODE_CTR, counter=ctr)
    return aes.decrypt(ciphertext[16:])

def nrf_hex_str_to_bytes(m_hex_str):
    split_nrf_plain_hex = x = m_hex_str.split(' ')
    split_nrf_plain_hex = "".join(split_nrf_plain_hex)
    return bytes.fromhex(split_nrf_plain_hex)



if __name__ == '__main__':
    #plain_key = 'NORDIC SEMICONDUCTORAES&MAC TEST'
    plain_key = 'NORDIC SEMICONDU'
    key = str.encode(plain_key)
    nrf_cipher = "12 DD C3 EE DF 6E 7E 04 C7 3B DD 0D A3 F5 8E 7E CF 6D A0 A6 76 60 8A 63 01 87 A5 F6 F6 26 B6 86 3A 07 B3 C0 FE D3 E5 3E 94 95 D5 05 EA 62 E7 23 4A F8 9A 20 4C 68 B2 2C D6 E5"
    nrf_cipher_iv = "00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 12 DD C3 EE DF 6E 7E 04 C7 3B DD 0D A3 F5 8E 7E CF 6D A0 A6 76 60 8A 63 01 87 A5 F6 F6 26 B6 86 3A 07 B3 C0 FE D3 E5 3E 94 95 D5 05 EA 62 E7 23 4A F8 9A 20 4C 68 B2 2C D6 E5"
    
    encrypted_byte = nrf_hex_str_to_bytes(nrf_cipher_iv)
    print(decrypt_message(key, encrypted_byte))

RE: Decrypting secret hex output from AES CTR example in 3rd party application (python)

Charlie — Mon, 28 Mar 2022 14:05:48 GMT

Hi Neel,

I test on AES Encryption: Encrypt and decrypt online — Cryptii seems everything works fine.

Here AES-128 use on 128bit key, so only "4E 4F 52 44 49 43 20 53 45 4D 49 43 4F 4E 44 55"(NORDIC SEMICONDU) is used.

Best regards,

Charlie

RE: Decrypting secret hex output from AES CTR example in 3rd party application (python)

Prantae — Fri, 25 Mar 2022 07:24:20 GMT

Does the encryption process have PKCS padding?

RE: Decrypting secret hex output from AES CTR example in 3rd party application (python)

Prantae — Fri, 25 Mar 2022 06:46:46 GMT

Thanks

RE: Decrypting secret hex output from AES CTR example in 3rd party application (python)

Charlie — Thu, 24 Mar 2022 12:07:46 GMT

Hi Neel,

I am checking the details with our development team and will feedback to you later.

Best regards,

Charlie