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Add support for decrypting System DPAPI secrets (#305)
Co-authored-by: Schamper <1254028+Schamper@users.noreply.github.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,151 @@ | ||
| from typing import Optional | ||
| from uuid import UUID | ||
|
|
||
| from dissect.cstruct import cstruct | ||
|
|
||
| from dissect.target.plugins.os.windows.dpapi.crypto import ( | ||
| CipherAlgorithm, | ||
| HashAlgorithm, | ||
| crypt_session_key_type1, | ||
| crypt_session_key_type2, | ||
| ) | ||
|
|
||
| blob_def = """ | ||
| struct DPAPIBlob { | ||
| DWORD dwVersion; | ||
| char provider[16]; | ||
| DWORD mkVersion; | ||
| char guid[16]; | ||
| DWORD flags; | ||
| DWORD descriptionLength; | ||
| char description[descriptionLength]; | ||
| DWORD CipherAlgId; | ||
| DWORD keyLen; | ||
| DWORD saltLength; | ||
| char salt[saltLength]; | ||
| DWORD strongLength; | ||
| char strong[strongLength]; | ||
| DWORD CryptAlgId; | ||
| DWORD hashLen; | ||
| DWORD hmacLength; | ||
| char hmac[hmacLength]; | ||
| DWORD cipherTextLength; | ||
| char cipherText[cipherTextLength]; | ||
| DWORD signLength; | ||
| char sign[signLength]; | ||
| }; | ||
| """ | ||
|
|
||
| c_blob = cstruct() | ||
| c_blob.load(blob_def) | ||
|
|
||
|
|
||
| class Blob: | ||
| """Represents a DPAPI blob.""" | ||
|
|
||
| def __init__(self, data: bytes): | ||
| self._blob = c_blob.DPAPIBlob(data) | ||
|
|
||
| self.version = self._blob.dwVersion | ||
| self.provider = str(UUID(bytes_le=self._blob.provider)) | ||
| self.mkversion = self._blob.mkVersion | ||
| self.guid = str(UUID(bytes_le=self._blob.guid)) | ||
| self.flags = self._blob.flags | ||
| self.description = self._blob.description.decode("utf-16-le") | ||
| self.cipher_algorithm = CipherAlgorithm.from_id(self._blob.CipherAlgId) | ||
| self.key_len = self._blob.keyLen | ||
| self.salt = self._blob.salt | ||
| self.strong = self._blob.strong | ||
| self.hash_algorithm = HashAlgorithm.from_id(self._blob.CryptAlgId) | ||
| self.hash_len = self._blob.hashLen | ||
| self.hmac = self._blob.hmac | ||
| self.cipher_text = self._blob.cipherText | ||
|
|
||
| # All the blob data between the version, provider and sign fields | ||
| # TODO: Replace with future offsetof function in cstruct | ||
| self.blob = data[c_blob.DPAPIBlob.lookup["mkVersion"].offset : -(self._blob.signLength + len(c_blob.DWORD))] | ||
| self.sign = self._blob.sign | ||
|
|
||
| self.clear_text = None | ||
| self.decrypted = False | ||
| self.sign_computed = None | ||
|
|
||
| def decrypt( | ||
| self, | ||
| master_key: bytes, | ||
| entropy: Optional[bytes] = None, | ||
| strong_password: Optional[str] = None, | ||
| smart_card_secret: Optional[bytes] = None, | ||
| ) -> bool: | ||
| """Try to decrypt the blob with the given master key. | ||
| Args: | ||
| master_key: Decrypted master key value. | ||
| entropy: Optional entropy for decrypting the blob. | ||
| strong_password: Optional password for decrypting the blob. | ||
| smart_card_secret: MS Next Gen Crypto secret (e.g. from PIN code). | ||
| Returns: | ||
| True if decryption is succesful, False otherwise. | ||
| """ | ||
| if self.decrypted: | ||
| return True | ||
|
|
||
| for algo in [crypt_session_key_type1, crypt_session_key_type2]: | ||
| session_key = algo( | ||
| master_key, | ||
| self.salt, | ||
| self.hash_algorithm, | ||
| entropy=entropy, | ||
| smart_card_secret=smart_card_secret, | ||
| strong_password=strong_password, | ||
| ) | ||
| key = self.cipher_algorithm.derive_key(session_key, self.hash_algorithm) | ||
| self.clear_text = self.cipher_algorithm.decrypt(self.cipher_text, key) | ||
|
|
||
| padding = self.clear_text[-1] | ||
| if padding <= self.cipher_algorithm.block_length: | ||
| self.clear_text = self.clear_text[:-padding] | ||
|
|
||
| # Check against provided HMAC | ||
| self.sign_computed = algo( | ||
| master_key, | ||
| self.hmac, | ||
| self.hash_algorithm, | ||
| entropy=entropy, | ||
| smart_card_secret=smart_card_secret, | ||
| verify_blob=self.blob, | ||
| ) | ||
|
|
||
| self.decrypted = self.sign_computed == self.sign | ||
| if self.decrypted: | ||
| return True | ||
|
|
||
| self.decrypted = False | ||
| return self.decrypted | ||
|
|
||
| def __repr__(self) -> str: | ||
| s = [ | ||
| "DPAPI BLOB", | ||
| "\n".join( | ||
| ( | ||
| "\tversion = %(version)d", | ||
| "\tprovider = %(provider)s", | ||
| "\tmkey = %(guid)s", | ||
| "\tflags = %(flags)#x", | ||
| "\tdescr = %(description)s", | ||
| "\tcipher_algo = %(cipher_algorithm)r", | ||
| "\thash_algo = %(hash_algorithm)r", | ||
| ) | ||
| ) | ||
| % self.__dict__, | ||
| "\tsalt = %s" % self.salt.hex(), | ||
| "\thmac = %s" % self.hmac.hex(), | ||
| "\tcipher = %s" % self.cipher_text.hex(), | ||
| "\tsign = %s" % self.sign.hex(), | ||
| ] | ||
| if self.sign_computed is not None: | ||
| s.append("\tsign_computed = %s" % self.sign_computed.hex()) | ||
| if self.clear_text is not None: | ||
| s.append("\tcleartext = %r" % self.clear_text) | ||
| return "\n".join(s) |
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