Decryptor for signalino - Midnight Sun CTF 2021

decrypt.py

#!/usr/bin/env python3

"""
Based on https://github.com/xperylabhub/ios_keychain_decrypter/blob/d7f3089067816cd2adc1ce910c9e1b927a356f37/keychain_decrypt.py#L113
"""

import plistlib
from bpylist import archiver, archive_types
import dataclasses
from Crypto.Cipher import AES
from pyasn1.codec.der.decoder import decode


@dataclasses.dataclass
class SFAuthenticatedCiphertext(archive_types.DataclassArchiver):
    SFCiphertext: bytes = b""
    SFInitializationVector: bytes = b""
    SFAuthenticationCode: bytes = b""


archiver.update_class_map({'_SFAuthenticatedCiphertext': SFAuthenticatedCiphertext})


def decript_entry(entry):
    if 'data' not in entry:
        return None
    c = archiver.unarchive(entry['data']['ciphertext'])

    unwrapedKey = entry['data']['unwrappedKey']
    authCode = c.SFAuthenticationCode
    iv = c.SFInitializationVector
    ciphertext = c.SFCiphertext

    gcm = AES.new(unwrapedKey, AES.MODE_GCM, iv)
    decrypted = gcm.decrypt_and_verify(ciphertext, authCode)
    decoded = decode(decrypted)[0]
    data = {}
    for k in decoded:
        if 'Octet' in str(type(k[1])):
            data.update({str(k[0]): bytes(k[1])})
        else:
            data.update({str(k[0]): str(k[1])})
    return data


if __name__ == "__main__":

    with open("backup_keychain_v2.plist", "rb") as f:
        plist = plistlib.load(f)

    for i in range(len(plist['keychainEntries'])):
        print("Entry {}".format(i))
        print(decript_entry(plist['keychainEntries'][i]))
        print("\n")