"""ACME Identifier Validation Challenges.""" import abc import codecs import functools import hashlib import logging import socket from typing import Any from typing import cast from typing import Dict from typing import Mapping from typing import Optional from typing import Tuple from typing import Type from typing import TypeVar from typing import Union from cryptography import x509 from cryptography.hazmat.primitives import hashes import josepy as jose from OpenSSL import crypto from OpenSSL import SSL import requests from acme import crypto_util from acme import errors logger = logging.getLogger(__name__) GenericChallenge = TypeVar('GenericChallenge', bound='Challenge') class Challenge(jose.TypedJSONObjectWithFields): # _fields_to_partial_json """ACME challenge.""" TYPES: Dict[str, Type['Challenge']] = {} @classmethod def from_json(cls: Type[GenericChallenge], jobj: Mapping[str, Any]) -> Union[GenericChallenge, 'UnrecognizedChallenge']: try: return cast(GenericChallenge, super().from_json(jobj)) except jose.UnrecognizedTypeError as error: logger.debug(error) return UnrecognizedChallenge.from_json(jobj) class ChallengeResponse(jose.TypedJSONObjectWithFields): # _fields_to_partial_json """ACME challenge response.""" TYPES: Dict[str, Type['ChallengeResponse']] = {} def to_partial_json(self) -> Dict[str, Any]: # Removes the `type` field which is inserted by TypedJSONObjectWithFields.to_partial_json. # This field breaks RFC8555 compliance. jobj = super().to_partial_json() jobj.pop(self.type_field_name, None) return jobj class UnrecognizedChallenge(Challenge): """Unrecognized challenge. ACME specification defines a generic framework for challenges and defines some standard challenges that are implemented in this module. However, other implementations (including peers) might define additional challenge types, which should be ignored if unrecognized. :ivar jobj: Original JSON decoded object. """ jobj: Dict[str, Any] def __init__(self, jobj: Mapping[str, Any]) -> None: super().__init__() object.__setattr__(self, "jobj", jobj) def to_partial_json(self) -> Dict[str, Any]: return self.jobj # pylint: disable=no-member @classmethod def from_json(cls, jobj: Mapping[str, Any]) -> 'UnrecognizedChallenge': return cls(jobj) class _TokenChallenge(Challenge): """Challenge with token. :ivar bytes token: """ TOKEN_SIZE = 128 // 8 # Based on the entropy value from the spec """Minimum size of the :attr:`token` in bytes.""" # TODO: acme-spec doesn't specify token as base64-encoded value token: bytes = jose.field( "token", encoder=jose.encode_b64jose, decoder=functools.partial( jose.decode_b64jose, size=TOKEN_SIZE, minimum=True)) # XXX: rename to ~token_good_for_url @property def good_token(self) -> bool: # XXX: @token.decoder """Is `token` good? .. todo:: acme-spec wants "It MUST NOT contain any non-ASCII characters", but it should also warrant that it doesn't contain ".." or "/"... """ # TODO: check that path combined with uri does not go above # URI_ROOT_PATH! # pylint: disable=unsupported-membership-test return b'..' not in self.token and b'/' not in self.token class KeyAuthorizationChallengeResponse(ChallengeResponse): """Response to Challenges based on Key Authorization. :param str key_authorization: """ key_authorization: str = jose.field("keyAuthorization") thumbprint_hash_function = hashes.SHA256 def verify(self, chall: 'KeyAuthorizationChallenge', account_public_key: jose.JWK) -> bool: """Verify the key authorization. :param KeyAuthorization chall: Challenge that corresponds to this response. :param JWK account_public_key: :return: ``True`` iff verification of the key authorization was successful. :rtype: bool """ parts = self.key_authorization.split('.') # pylint: disable=no-member if len(parts) != 2: logger.debug("Key authorization (%r) is not well formed", self.key_authorization) return False if parts[0] != chall.encode("token"): logger.debug("Mismatching token in key authorization: " "%r instead of %r", parts[0], chall.encode("token")) return False thumbprint = jose.b64encode(account_public_key.thumbprint( hash_function=self.thumbprint_hash_function)).decode() if parts[1] != thumbprint: logger.debug("Mismatching thumbprint in key authorization: " "%r instead of %r", parts[0], thumbprint) return False return True def to_partial_json(self) -> Dict[str, Any]: jobj = super().to_partial_json() jobj.pop('keyAuthorization', None) return jobj # TODO: Make this method a generic of K (bound=KeyAuthorizationChallenge), response_cls of type # Type[K] and use it in response/response_and_validation return types once Python 3.6 support is # dropped (do not support generic ABC classes, see https://github.com/python/typing/issues/449). class KeyAuthorizationChallenge(_TokenChallenge, metaclass=abc.ABCMeta): """Challenge based on Key Authorization. :param response_cls: Subclass of `KeyAuthorizationChallengeResponse` that will be used to generate ``response``. :param str typ: type of the challenge """ typ: str = NotImplemented response_cls: Type[KeyAuthorizationChallengeResponse] = NotImplemented thumbprint_hash_function = ( KeyAuthorizationChallengeResponse.thumbprint_hash_function) def key_authorization(self, account_key: jose.JWK) -> str: """Generate Key Authorization. :param JWK account_key: :rtype str: """ return self.encode("token") + "." + jose.b64encode( account_key.thumbprint( hash_function=self.thumbprint_hash_function)).decode() def response(self, account_key: jose.JWK) -> KeyAuthorizationChallengeResponse: """Generate response to the challenge. :param JWK account_key: :returns: Response (initialized `response_cls`) to the challenge. :rtype: KeyAuthorizationChallengeResponse """ return self.response_cls( # pylint: disable=not-callable key_authorization=self.key_authorization(account_key)) @abc.abstractmethod def validation(self, account_key: jose.JWK, **kwargs: Any) -> Any: """Generate validation for the challenge. Subclasses must implement this method, but they are likely to return completely different data structures, depending on what's necessary to complete the challenge. Interpretation of that return value must be known to the caller. :param JWK account_key: :returns: Challenge-specific validation. """ raise NotImplementedError() # pragma: no cover def response_and_validation(self, account_key: jose.JWK, *args: Any, **kwargs: Any ) -> Tuple[KeyAuthorizationChallengeResponse, Any]: """Generate response and validation. Convenience function that return results of `response` and `validation`. :param JWK account_key: :rtype: tuple """ return (self.response(account_key), self.validation(account_key, *args, **kwargs)) @ChallengeResponse.register class DNS01Response(KeyAuthorizationChallengeResponse): """ACME dns-01 challenge response.""" typ = "dns-01" def simple_verify(self, chall: 'DNS01', domain: str, account_public_key: jose.JWK) -> bool: # pylint: disable=unused-argument """Simple verify. This method no longer checks DNS records and is a simple wrapper around `KeyAuthorizationChallengeResponse.verify`. :param challenges.DNS01 chall: Corresponding challenge. :param str domain: Domain name being verified. :param JWK account_public_key: Public key for the key pair being authorized. :return: ``True`` iff verification of the key authorization was successful. :rtype: bool """ verified = self.verify(chall, account_public_key) if not verified: logger.debug("Verification of key authorization in response failed") return verified @Challenge.register class DNS01(KeyAuthorizationChallenge): """ACME dns-01 challenge.""" response_cls = DNS01Response typ = response_cls.typ LABEL = "_acme-challenge" """Label clients prepend to the domain name being validated.""" def validation(self, account_key: jose.JWK, **unused_kwargs: Any) -> str: """Generate validation. :param JWK account_key: :rtype: str """ return jose.b64encode(hashlib.sha256(self.key_authorization( account_key).encode("utf-8")).digest()).decode() def validation_domain_name(self, name: str) -> str: """Domain name for TXT validation record. :param str name: Domain name being validated. :rtype: str """ return f"{self.LABEL}.{name}" @ChallengeResponse.register class HTTP01Response(KeyAuthorizationChallengeResponse): """ACME http-01 challenge response.""" typ = "http-01" PORT = 80 """Verification port as defined by the protocol. You can override it (e.g. for testing) by passing ``port`` to `simple_verify`. """ WHITESPACE_CUTSET = "\n\r\t " """Whitespace characters which should be ignored at the end of the body.""" def simple_verify(self, chall: 'HTTP01', domain: str, account_public_key: jose.JWK, port: Optional[int] = None, timeout: int = 30) -> bool: """Simple verify. :param challenges.SimpleHTTP chall: Corresponding challenge. :param str domain: Domain name being verified. :param JWK account_public_key: Public key for the key pair being authorized. :param int port: Port used in the validation. :param int timeout: Timeout in seconds. :returns: ``True`` iff validation with the files currently served by the HTTP server is successful. :rtype: bool """ if not self.verify(chall, account_public_key): logger.debug("Verification of key authorization in response failed") return False # TODO: ACME specification defines URI template that doesn't # allow to use a custom port... Make sure port is not in the # request URI, if it's standard. if port is not None and port != self.PORT: logger.warning( "Using non-standard port for http-01 verification: %s", port) domain += ":{0}".format(port) uri = chall.uri(domain) logger.debug("Verifying %s at %s...", chall.typ, uri) try: http_response = requests.get(uri, verify=False, timeout=timeout) except requests.exceptions.RequestException as error: logger.error("Unable to reach %s: %s", uri, error) return False # By default, http_response.text will try to guess the encoding to use # when decoding the response to Python unicode strings. This guesswork # is error prone. RFC 8555 specifies that HTTP-01 responses should be # key authorizations with possible trailing whitespace. Since key # authorizations must be composed entirely of the base64url alphabet # plus ".", we tell requests that the response should be ASCII. See # https://datatracker.ietf.org/doc/html/rfc8555#section-8.3 for more # info. http_response.encoding = "ascii" logger.debug("Received %s: %s. Headers: %s", http_response, http_response.text, http_response.headers) challenge_response = http_response.text.rstrip(self.WHITESPACE_CUTSET) if self.key_authorization != challenge_response: logger.debug("Key authorization from response (%r) doesn't match " "HTTP response (%r)", self.key_authorization, challenge_response) return False return True @Challenge.register class HTTP01(KeyAuthorizationChallenge): """ACME http-01 challenge.""" response_cls = HTTP01Response typ = response_cls.typ URI_ROOT_PATH = ".well-known/acme-challenge" """URI root path for the server provisioned resource.""" @property def path(self) -> str: """Path (starting with '/') for provisioned resource. :rtype: str """ return '/' + self.URI_ROOT_PATH + '/' + self.encode('token') def uri(self, domain: str) -> str: """Create an URI to the provisioned resource. Forms an URI to the HTTPS server provisioned resource (containing :attr:`~SimpleHTTP.token`). :param str domain: Domain name being verified. :rtype: str """ return "http://" + domain + self.path def validation(self, account_key: jose.JWK, **unused_kwargs: Any) -> str: """Generate validation. :param JWK account_key: :rtype: str """ return self.key_authorization(account_key) @ChallengeResponse.register class TLSALPN01Response(KeyAuthorizationChallengeResponse): """ACME tls-alpn-01 challenge response.""" typ = "tls-alpn-01" PORT = 443 """Verification port as defined by the protocol. You can override it (e.g. for testing) by passing ``port`` to `simple_verify`. """ ID_PE_ACME_IDENTIFIER_V1 = b"1.3.6.1.5.5.7.1.30.1" ACME_TLS_1_PROTOCOL = b"acme-tls/1" @property def h(self) -> bytes: """Hash value stored in challenge certificate""" return hashlib.sha256(self.key_authorization.encode('utf-8')).digest() def gen_cert(self, domain: str, key: Optional[crypto.PKey] = None, bits: int = 2048 ) -> Tuple[crypto.X509, crypto.PKey]: """Generate tls-alpn-01 certificate. :param str domain: Domain verified by the challenge. :param OpenSSL.crypto.PKey key: Optional private key used in certificate generation. If not provided (``None``), then fresh key will be generated. :param int bits: Number of bits for newly generated key. :rtype: `tuple` of `OpenSSL.crypto.X509` and `OpenSSL.crypto.PKey` """ if key is None: key = crypto.PKey() key.generate_key(crypto.TYPE_RSA, bits) der_value = b"DER:" + codecs.encode(self.h, 'hex') acme_extension = crypto.X509Extension(self.ID_PE_ACME_IDENTIFIER_V1, critical=True, value=der_value) return crypto_util.gen_ss_cert(key, [domain], force_san=True, extensions=[acme_extension]), key def probe_cert(self, domain: str, host: Optional[str] = None, port: Optional[int] = None) -> crypto.X509: """Probe tls-alpn-01 challenge certificate. :param str domain: domain being validated, required. :param str host: IP address used to probe the certificate. :param int port: Port used to probe the certificate. """ if host is None: host = socket.gethostbyname(domain) logger.debug('%s resolved to %s', domain, host) if port is None: port = self.PORT return crypto_util.probe_sni(host=host.encode(), port=port, name=domain.encode(), alpn_protocols=[self.ACME_TLS_1_PROTOCOL]) def verify_cert(self, domain: str, cert: Union[x509.Certificate, crypto.X509]) -> bool: """Verify tls-alpn-01 challenge certificate. :param str domain: Domain name being validated. :param cert: Challenge certificate. :type cert: `cryptography.x509.Certificate` or `OpenSSL.crypto.X509` :returns: Whether the certificate was successfully verified. :rtype: bool """ if not isinstance(cert, x509.Certificate): cert = cert.to_cryptography() names = crypto_util.get_names_from_subject_and_extensions( cert.subject, cert.extensions ) logger.debug( "Certificate %s. SANs: %s", cert.fingerprint(hashes.SHA256()), names ) if len(names) != 1 or names[0].lower() != domain.lower(): return False try: ext = cert.extensions.get_extension_for_oid( x509.ObjectIdentifier(self.ID_PE_ACME_IDENTIFIER_V1.decode()) ) except x509.ExtensionNotFound: return False # This is for the type checker. assert isinstance(ext.value, x509.UnrecognizedExtension) return ext.value.value == self.h # pylint: disable=too-many-arguments def simple_verify(self, chall: 'TLSALPN01', domain: str, account_public_key: jose.JWK, cert: Optional[crypto.X509] = None, host: Optional[str] = None, port: Optional[int] = None) -> bool: """Simple verify. Verify ``validation`` using ``account_public_key``, optionally probe tls-alpn-01 certificate and check using `verify_cert`. :param .challenges.TLSALPN01 chall: Corresponding challenge. :param str domain: Domain name being validated. :param JWK account_public_key: :param OpenSSL.crypto.X509 cert: Optional certificate. If not provided (``None``) certificate will be retrieved using `probe_cert`. :param string host: IP address used to probe the certificate. :param int port: Port used to probe the certificate. :returns: ``True`` if and only if client's control of the domain has been verified. :rtype: bool """ if not self.verify(chall, account_public_key): logger.debug("Verification of key authorization in response failed") return False if cert is None: try: cert = self.probe_cert(domain=domain, host=host, port=port) except errors.Error as error: logger.debug(str(error), exc_info=True) return False return self.verify_cert(domain, cert) @Challenge.register # pylint: disable=too-many-ancestors class TLSALPN01(KeyAuthorizationChallenge): """ACME tls-alpn-01 challenge.""" response_cls = TLSALPN01Response typ = response_cls.typ def validation(self, account_key: jose.JWK, **kwargs: Any) -> Tuple[crypto.X509, crypto.PKey]: """Generate validation. :param JWK account_key: :param str domain: Domain verified by the challenge. :param OpenSSL.crypto.PKey cert_key: Optional private key used in certificate generation. If not provided (``None``), then fresh key will be generated. :rtype: `tuple` of `OpenSSL.crypto.X509` and `OpenSSL.crypto.PKey` """ # TODO: Remove cast when response() is generic. return cast(TLSALPN01Response, self.response(account_key)).gen_cert( key=kwargs.get('cert_key'), domain=cast(str, kwargs.get('domain'))) @staticmethod def is_supported() -> bool: """ Check if TLS-ALPN-01 challenge is supported on this machine. This implies that a recent version of OpenSSL is installed (>= 1.0.2), or a recent cryptography version shipped with the OpenSSL library is installed. :returns: ``True`` if TLS-ALPN-01 is supported on this machine, ``False`` otherwise. :rtype: bool """ return (hasattr(SSL.Connection, "set_alpn_protos") and hasattr(SSL.Context, "set_alpn_select_callback")) @Challenge.register class DNS(_TokenChallenge): """ACME "dns" challenge.""" typ = "dns" LABEL = "_acme-challenge" """Label clients prepend to the domain name being validated.""" def gen_validation(self, account_key: jose.JWK, alg: jose.JWASignature = jose.RS256, **kwargs: Any) -> jose.JWS: """Generate validation. :param .JWK account_key: Private account key. :param .JWA alg: :returns: This challenge wrapped in `.JWS` :rtype: .JWS """ return jose.JWS.sign( payload=self.json_dumps(sort_keys=True).encode('utf-8'), key=account_key, alg=alg, **kwargs) def check_validation(self, validation: jose.JWS, account_public_key: jose.JWK) -> bool: """Check validation. :param JWS validation: :param JWK account_public_key: :rtype: bool """ if not validation.verify(key=account_public_key): return False try: return self == self.json_loads( validation.payload.decode('utf-8')) except jose.DeserializationError as error: logger.debug("Checking validation for DNS failed: %s", error) return False def gen_response(self, account_key: jose.JWK, **kwargs: Any) -> 'DNSResponse': """Generate response. :param .JWK account_key: Private account key. :param .JWA alg: :rtype: DNSResponse """ return DNSResponse(validation=self.gen_validation(account_key, **kwargs)) def validation_domain_name(self, name: str) -> str: """Domain name for TXT validation record. :param str name: Domain name being validated. """ return "{0}.{1}".format(self.LABEL, name) @ChallengeResponse.register class DNSResponse(ChallengeResponse): """ACME "dns" challenge response. :param JWS validation: """ typ = "dns" validation: jose.JWS = jose.field("validation", decoder=jose.JWS.from_json) def check_validation(self, chall: 'DNS', account_public_key: jose.JWK) -> bool: """Check validation. :param challenges.DNS chall: :param JWK account_public_key: :rtype: bool """ return chall.check_validation(self.validation, account_public_key)