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import base64
import pathlib
from Crypto.Cipher import AES
from Crypto.Util import Counter
def decrypt_security_token(security_token: str) -> (str, str):
"""
The `decrypt_security_token` function decrypts a security token into a key and nonce pair using AES
encryption.
Args:
security_token (str): The `security_token` parameter in the `decrypt_security_token` function is a
string that represents an encrypted security token. This function decrypts the security token into a
key and nonce pair using AES encryption. security_token should match the securityToken value from the web response.
Returns:
The `decrypt_security_token` function returns a tuple containing the key and nonce extracted from
the decrypted security token.
"""
# Do not change this
master_key = "UIlTTEMmmLfGowo/UC60x2H45W6MdGgTRfo/umg4754="
# Decode the base64 strings to ascii strings
master_key = base64.b64decode(master_key)
security_token = base64.b64decode(security_token)
# Get the IV from the first 16 bytes of the securityToken
iv = security_token[:16]
encrypted_st = security_token[16:]
# Initialize decryptor
decryptor = AES.new(master_key, AES.MODE_CBC, iv)
# Decrypt the security token
decrypted_st = decryptor.decrypt(encrypted_st)
# Get the audio stream decryption key and nonce from the decrypted security token
key = decrypted_st[:16]
nonce = decrypted_st[16:24]
return key, nonce
def decrypt_file(path_file_encrypted: pathlib.Path, path_file_destination: pathlib.Path, key: str, nonce: str) -> None:
"""
Decrypts an encrypted MQA file given the file, key and nonce.
TODO: Is it really only necessary for MQA of for all other formats, too?
"""
# Initialize counter and file decryptor
counter = Counter.new(64, prefix=nonce, initial_value=0)
decryptor = AES.new(key, AES.MODE_CTR, counter=counter)
# Open and decrypt
with path_file_encrypted.open("rb") as f_src:
audio_decrypted = decryptor.decrypt(f_src.read())
# Replace with decrypted file
with path_file_destination.open("wb") as f_dst:
f_dst.write(audio_decrypted)
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