# Copyright 2017-2019, Damian Johnson and The Tor Project
# See LICENSE for licensing information
"""
Parsing for `Tor Ed25519 certificates
<https://gitweb.torproject.org/torspec.git/tree/cert-spec.txt>`_, which are
used to for a variety of purposes...
* validating the key used to sign server descriptors
* validating the key used to sign hidden service v3 descriptors
* signing and encrypting hidden service v3 indroductory points
.. versionadded:: 1.6.0
**Module Overview:**
::
Ed25519Certificate - Ed25519 signing key certificate
| +- Ed25519CertificateV1 - version 1 Ed25519 certificate
| |- is_expired - checks if certificate is presently expired
| |- signing_key - certificate signing key
| +- validate - validates a descriptor's signature
|
|- from_base64 - decodes a base64 encoded certificate
|- to_base64 - base64 encoding of this certificate
|
|- unpack - decodes a byte encoded certificate
+- pack - byte encoding of this certificate
Ed25519Extension - extension included within an Ed25519Certificate
.. data:: CertType (enum)
Purpose of Ed25519 certificate. For more information see...
* `cert-spec.txt <https://gitweb.torproject.org/torspec.git/tree/cert-spec.txt>`_ section A.1
* `rend-spec-v3.txt <https://gitweb.torproject.org/torspec.git/tree/rend-spec-v3.txt>`_ appendix E
.. deprecated:: 1.8.0
Replaced with :data:`stem.client.datatype.CertType`
======================== ===========
CertType Description
======================== ===========
**SIGNING** signing key with an identity key
**LINK_CERT** TLS link certificate signed with ed25519 signing key
**AUTH** authentication key signed with ed25519 signing key
**HS_V3_DESC_SIGNING** hidden service v3 short-term descriptor signing key
**HS_V3_INTRO_AUTH** hidden service v3 introductory point authentication key
**HS_V3_INTRO_ENCRYPT** hidden service v3 introductory point encryption key
======================== ===========
.. data:: ExtensionType (enum)
Recognized exception types.
==================== ===========
ExtensionType Description
==================== ===========
**HAS_SIGNING_KEY** includes key used to sign the certificate
==================== ===========
.. data:: ExtensionFlag (enum)
Flags that can be assigned to Ed25519 certificate extensions.
====================== ===========
ExtensionFlag Description
====================== ===========
**AFFECTS_VALIDATION** extension affects whether the certificate is valid
**UNKNOWN** extension includes flags not yet recognized by stem
====================== ===========
"""
import base64
import binascii
import datetime
import hashlib
import re
import stem.descriptor.hidden_service
import stem.descriptor.server_descriptor
import stem.prereq
import stem.util
import stem.util.enum
import stem.util.str_tools
from stem.client.datatype import Field, Size, split
# TODO: Importing under an alternate name until we can deprecate our redundant
# CertType enum in Stem 2.x.
from stem.client.datatype import CertType as ClientCertType
ED25519_KEY_LENGTH = 32
ED25519_HEADER_LENGTH = 40
ED25519_SIGNATURE_LENGTH = 64
SIG_PREFIX_SERVER_DESC = b'Tor router descriptor signature v1'
SIG_PREFIX_HS_V3 = b'Tor onion service descriptor sig v3'
DEFAULT_EXPIRATION_HOURS = 54 # HSv3 certificate expiration of tor
CertType = stem.util.enum.UppercaseEnum(
'SIGNING',
'LINK_CERT',
'AUTH',
'HS_V3_DESC_SIGNING',
'HS_V3_INTRO_AUTH',
'HS_V3_INTRO_ENCRYPT',
)
ExtensionType = stem.util.enum.Enum(('HAS_SIGNING_KEY', 4),)
ExtensionFlag = stem.util.enum.UppercaseEnum('AFFECTS_VALIDATION', 'UNKNOWN')
[docs]class Ed25519Extension(Field):
"""
Extension within an Ed25519 certificate.
:var stem.descriptor.certificate.ExtensionType type: extension type
:var list flags: extension attribute flags
:var int flag_int: integer encoding of the extension attribute flags
:var bytes data: data the extension concerns
"""
def __init__(self, ext_type, flag_val, data):
self.type = ext_type
self.flags = []
self.flag_int = flag_val if flag_val else 0
self.data = data
if flag_val and flag_val % 2 == 1:
self.flags.append(ExtensionFlag.AFFECTS_VALIDATION)
flag_val -= 1
if flag_val:
self.flags.append(ExtensionFlag.UNKNOWN)
if ext_type == ExtensionType.HAS_SIGNING_KEY and len(data) != 32:
raise ValueError('Ed25519 HAS_SIGNING_KEY extension must be 32 bytes, but was %i.' % len(data))
[docs] def pack(self):
encoded = bytearray()
encoded += Size.SHORT.pack(len(self.data))
encoded += Size.CHAR.pack(self.type)
encoded += Size.CHAR.pack(self.flag_int)
encoded += self.data
return bytes(encoded)
@staticmethod
[docs] def pop(content):
if len(content) < 4:
raise ValueError('Ed25519 extension is missing header fields')
data_size, content = Size.SHORT.pop(content)
ext_type, content = Size.CHAR.pop(content)
flags, content = Size.CHAR.pop(content)
data, content = split(content, data_size)
if len(data) != data_size:
raise ValueError("Ed25519 extension is truncated. It should have %i bytes of data but there's only %i." % (data_size, len(data)))
return Ed25519Extension(ext_type, flags, data), content
def __hash__(self):
return stem.util._hash_attr(self, 'type', 'flag_int', 'data', cache = True)
[docs]class Ed25519Certificate(object):
"""
Base class for an Ed25519 certificate.
:var int version: certificate format version
:var unicode encoded: base64 encoded ed25519 certificate
"""
def __init__(self, version):
self.version = version
self.encoded = None # TODO: remove in stem 2.x
@staticmethod
[docs] def unpack(content):
"""
Parses a byte encoded ED25519 certificate.
:param bytes content: encoded certificate
:returns: :class:`~stem.descriptor.certificate.Ed25519Certificate` subclsss
for the given certificate
:raises: **ValueError** if certificate is malformed
"""
version = Size.CHAR.pop(content)[0]
if version == 1:
return Ed25519CertificateV1.unpack(content)
else:
raise ValueError('Ed25519 certificate is version %i. Parser presently only supports version 1.' % version)
@staticmethod
[docs] def from_base64(content):
"""
Parses a base64 encoded ED25519 certificate.
:param str content: base64 encoded certificate
:returns: :class:`~stem.descriptor.certificate.Ed25519Certificate` subclsss
for the given certificate
:raises: **ValueError** if content is malformed
"""
content = stem.util.str_tools._to_unicode(content)
if content.startswith('-----BEGIN ED25519 CERT-----\n') and content.endswith('\n-----END ED25519 CERT-----'):
content = content[29:-27]
try:
decoded = base64.b64decode(content)
if not decoded:
raise TypeError('empty')
instance = Ed25519Certificate.unpack(decoded)
instance.encoded = content
return instance
except (TypeError, binascii.Error) as exc:
raise ValueError("Ed25519 certificate wasn't propoerly base64 encoded (%s):\n%s" % (exc, content))
[docs] def pack(self):
"""
Encoded byte representation of our certificate.
:returns: **bytes** for our encoded certificate representation
"""
raise NotImplementedError('Certificate encoding has not been implemented for %s' % type(self).__name__)
[docs] def to_base64(self, pem = False):
"""
Base64 encoded certificate data.
:param bool pem: include `PEM header/footer
<https://en.wikipedia.org/wiki/Privacy-Enhanced_Mail>`_, for more
information see `RFC 7468 <https://tools.ietf.org/html/rfc7468>`_
:returns: **unicode** for our encoded certificate representation
"""
encoded = b'\n'.join(stem.util.str_tools._split_by_length(base64.b64encode(self.pack()), 64))
if pem:
encoded = b'-----BEGIN ED25519 CERT-----\n%s\n-----END ED25519 CERT-----' % encoded
return stem.util.str_tools._to_unicode(encoded)
@staticmethod
def _from_descriptor(keyword, attribute):
def _parse(descriptor, entries):
value, block_type, block_contents = entries[keyword][0]
if not block_contents or block_type != 'ED25519 CERT':
raise ValueError("'%s' should be followed by a ED25519 CERT block, but was a %s" % (keyword, block_type))
setattr(descriptor, attribute, Ed25519Certificate.from_base64(block_contents))
return _parse
def __str__(self):
return self.to_base64(pem = True)
@staticmethod
[docs] def parse(content):
return Ed25519Certificate.from_base64(content) # TODO: drop this alias in stem 2.x
[docs]class Ed25519CertificateV1(Ed25519Certificate):
"""
Version 1 Ed25519 certificate, which are used for signing tor server
descriptors.
:var stem.client.datatype.CertType type: certificate purpose
:var int type_int: integer value of the certificate purpose
:var datetime expiration: expiration of the certificate
:var int key_type: format of the key
:var bytes key: key content
:var list extensions: :class:`~stem.descriptor.certificate.Ed25519Extension` in this certificate
:var bytes signature: certificate signature
:param bytes signature: pre-calculated certificate signature
:param cryptography.hazmat.primitives.asymmetric.ed25519.Ed25519PrivateKey signing_key: certificate signing key
"""
def __init__(self, cert_type = None, expiration = None, key_type = None, key = None, extensions = None, signature = None, signing_key = None):
super(Ed25519CertificateV1, self).__init__(1)
if cert_type is None:
raise ValueError('Certificate type is required')
elif key is None:
raise ValueError('Certificate key is required')
self.type, self.type_int = ClientCertType.get(cert_type)
self.expiration = expiration if expiration else datetime.datetime.utcnow() + datetime.timedelta(hours = DEFAULT_EXPIRATION_HOURS)
self.key_type = key_type if key_type else 1
self.key = stem.util._pubkey_bytes(key)
self.extensions = extensions if extensions else []
self.signature = signature
if signing_key:
calculated_sig = signing_key.sign(self.pack())
# if caller provides both signing key *and* signature then ensure they match
if self.signature and self.signature != calculated_sig:
raise ValueError("Signature calculated from its key (%s) mismatches '%s'" % (calculated_sig, self.signature))
self.signature = calculated_sig
if self.type in (ClientCertType.LINK, ClientCertType.IDENTITY, ClientCertType.AUTHENTICATE):
raise ValueError('Ed25519 certificate cannot have a type of %i. This is reserved for CERTS cells.' % self.type_int)
elif self.type == ClientCertType.ED25519_IDENTITY:
raise ValueError('Ed25519 certificate cannot have a type of 7. This is reserved for RSA identity cross-certification.')
elif self.type == ClientCertType.UNKNOWN:
raise ValueError('Ed25519 certificate type %i is unrecognized' % self.type_int)
[docs] def pack(self):
encoded = bytearray()
encoded += Size.CHAR.pack(self.version)
encoded += Size.CHAR.pack(self.type_int)
encoded += Size.LONG.pack(int(stem.util.datetime_to_unix(self.expiration) / 3600))
encoded += Size.CHAR.pack(self.key_type)
encoded += self.key
encoded += Size.CHAR.pack(len(self.extensions))
for extension in self.extensions:
encoded += extension.pack()
if self.signature:
encoded += self.signature
return bytes(encoded)
@staticmethod
[docs] def unpack(content):
if len(content) < ED25519_HEADER_LENGTH + ED25519_SIGNATURE_LENGTH:
raise ValueError('Ed25519 certificate was %i bytes, but should be at least %i' % (len(content), ED25519_HEADER_LENGTH + ED25519_SIGNATURE_LENGTH))
header, signature = split(content, len(content) - ED25519_SIGNATURE_LENGTH)
version, header = Size.CHAR.pop(header)
cert_type, header = Size.CHAR.pop(header)
expiration_hours, header = Size.LONG.pop(header)
key_type, header = Size.CHAR.pop(header)
key, header = split(header, ED25519_KEY_LENGTH)
extension_count, extension_data = Size.CHAR.pop(header)
if version != 1:
raise ValueError('Ed25519 v1 parser cannot read version %i certificates' % version)
extensions = []
for i in range(extension_count):
extension, extension_data = Ed25519Extension.pop(extension_data)
extensions.append(extension)
if extension_data:
raise ValueError('Ed25519 certificate had %i bytes of unused extension data' % len(extension_data))
return Ed25519CertificateV1(cert_type, datetime.datetime.utcfromtimestamp(expiration_hours * 3600), key_type, key, extensions, signature)
[docs] def is_expired(self):
"""
Checks if this certificate is presently expired or not.
:returns: **True** if the certificate has expired, **False** otherwise
"""
return datetime.datetime.now() > self.expiration
[docs] def signing_key(self):
"""
Provides this certificate's signing key.
.. versionadded:: 1.8.0
:returns: **bytes** with the first signing key on the certificate, None if
not present
"""
for extension in self.extensions:
if extension.type == ExtensionType.HAS_SIGNING_KEY:
return extension.data
return None
[docs] def validate(self, descriptor):
"""
Validate our descriptor content matches its ed25519 signature. Supported
descriptor types include...
* :class:`~stem.descriptor.server_descriptor.RelayDescriptor`
* :class:`~stem.descriptor.hidden_service.HiddenServiceDescriptorV3`
:param stem.descriptor.__init__.Descriptor descriptor: descriptor to validate
:raises:
* **ValueError** if signing key or descriptor are invalid
* **TypeError** if descriptor type is unsupported
* **ImportError** if cryptography module or ed25519 support unavailable
"""
if not stem.prereq.is_crypto_available(ed25519 = True):
raise ImportError('Certificate validation requires the cryptography module and ed25519 support')
if isinstance(descriptor, stem.descriptor.server_descriptor.RelayDescriptor):
signed_content = hashlib.sha256(Ed25519CertificateV1._signed_content(descriptor)).digest()
signature = stem.util.str_tools._decode_b64(descriptor.ed25519_signature)
self._validate_server_desc_signing_key(descriptor)
elif isinstance(descriptor, stem.descriptor.hidden_service.HiddenServiceDescriptorV3):
signed_content = Ed25519CertificateV1._signed_content(descriptor)
signature = stem.util.str_tools._decode_b64(descriptor.signature)
else:
raise TypeError('Certificate validation only supported for server and hidden service descriptors, not %s' % type(descriptor).__name__)
from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PublicKey
from cryptography.exceptions import InvalidSignature
try:
key = Ed25519PublicKey.from_public_bytes(self.key)
key.verify(signature, signed_content)
except InvalidSignature:
raise ValueError('Descriptor Ed25519 certificate signature invalid (signature forged or corrupt)')
@staticmethod
def _signed_content(descriptor):
"""
Provides this descriptor's signing constant, appended with the portion of
the descriptor that's signed.
"""
if isinstance(descriptor, stem.descriptor.server_descriptor.RelayDescriptor):
prefix = SIG_PREFIX_SERVER_DESC
regex = b'(.+router-sig-ed25519 )'
elif isinstance(descriptor, stem.descriptor.hidden_service.HiddenServiceDescriptorV3):
prefix = SIG_PREFIX_HS_V3
regex = b'(.+)signature '
else:
raise ValueError('BUG: %s type unexpected' % type(descriptor).__name__)
match = re.search(regex, descriptor.get_bytes(), re.DOTALL)
if not match:
raise ValueError('Malformed descriptor missing signature line')
return prefix + match.group(1)
def _validate_server_desc_signing_key(self, descriptor):
from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PublicKey
from cryptography.exceptions import InvalidSignature
if descriptor.ed25519_master_key:
signing_key = base64.b64decode(stem.util.str_tools._to_bytes(descriptor.ed25519_master_key) + b'=')
else:
signing_key = self.signing_key()
if not signing_key:
raise ValueError('Server descriptor missing an ed25519 signing key')
try:
key = Ed25519PublicKey.from_public_bytes(signing_key)
key.verify(self.signature, base64.b64decode(stem.util.str_tools._to_bytes(self.encoded))[:-ED25519_SIGNATURE_LENGTH])
except InvalidSignature:
raise ValueError('Ed25519KeyCertificate signing key is invalid (signature forged or corrupt)')
