OCSP response builder (#4485)

* ocsp response builder

* better prose

* review changes

5 files changed, 846 insertions, 10 deletions

diff --git a/docs/x509/ocsp.rst b/docs/x509/ocsp.rst
index 499e7a91..535ffdda 100644
--- a/docs/x509/ocsp.rst
+++ b/docs/x509/ocsp.rst
@@ -68,6 +68,24 @@ OCSP
     gP8L8mJMcCaY
     -----END CERTIFICATE-----
     """
+    pem_responder_cert = b"""
+    -----BEGIN CERTIFICATE-----
+    MIIBPjCB5KADAgECAgQHW80VMAoGCCqGSM49BAMCMCcxCzAJBgNVBAYTAlVTMRgw
+    FgYDVQQDDA9DcnlwdG9ncmFwaHkgQ0EwHhcNMTgxMDA3MTIzNTEwWhcNMjgxMDA0
+    MTIzNTEwWjAnMQswCQYDVQQGEwJVUzEYMBYGA1UEAwwPQ3J5cHRvZ3JhcGh5IENB
+    MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEbQ2E0N/E3R0zEG+qa+yAFXBY6Fte
+    QzyvFdq7EZHDktlyUllaVJBrbX1ItV0MlayFwwQPhZmuLPpQBzuVKyrUfTAKBggq
+    hkjOPQQDAgNJADBGAiEAo0NQRmfPvhWQpSvJzV+2Ag441Zeckk+bib7swduQIjIC
+    IQCqYD9pArB2SWfmhQCSZkNEATlsPIML8lvlSkbNcrmrqQ==
+    -----END CERTIFICATE-----
+    """
+    pem_responder_key = b"""
+    -----BEGIN PRIVATE KEY-----
+    MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgO+vsRu8xDIVZE+xh
+    s8ESqJqcpJlwmj8CtF8HPHxrDSGhRANCAARtDYTQ38TdHTMQb6pr7IAVcFjoW15D
+    PK8V2rsRkcOS2XJSWVpUkGttfUi1XQyVrIXDBA+Fma4s+lAHO5UrKtR9
+    -----END PRIVATE KEY-----
+    """
     der_ocsp_req = (
         b"0V0T0R0P0N0\t\x06\x05+\x0e\x03\x02\x1a\x05\x00\x04\x148\xcaF\x8c"
         b"\x07D\x8d\xf4\x81\x96\xc7mmLpQ\x9e`\xa7\xbd\x04\x14yu\xbb\x84:\xcb"
@@ -183,6 +201,156 @@ Loading Responses
         OCSPResponseStatus.UNAUTHORIZED
 
 
+Creating Responses
+~~~~~~~~~~~~~~~~~~
+
+.. class:: OCSPResponseBuilder
+
+    .. versionadded:: 2.4
+
+    This class is used to create :class:`~cryptography.x509.ocsp.OCSPResponse`
+    objects. You cannot set ``produced_at`` on OCSP responses at this time.
+    Instead the field is set to current UTC time when calling ``sign``. For
+    unsuccessful statuses call the class method
+    :meth:`~cryptography.x509.ocsp.OCSPResponseBuilder.build_unsuccessful`.
+
+    .. method:: add_response(cert, issuer, algorithm, cert_status, this_update, next_update, revocation_time, revocation_reason)
+
+        This method adds status information about the certificate that was
+        requested to the response.
+
+        :param cert: The :class:`~cryptography.x509.Certificate` whose validity
+            is being checked.
+
+        :param issuer: The issuer :class:`~cryptography.x509.Certificate` of
+            the certificate that is being checked.
+
+        :param algorithm: A
+            :class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm`
+            instance. For OCSP only
+            :class:`~cryptography.hazmat.primitives.hashes.SHA1`,
+            :class:`~cryptography.hazmat.primitives.hashes.SHA224`,
+            :class:`~cryptography.hazmat.primitives.hashes.SHA256`,
+            :class:`~cryptography.hazmat.primitives.hashes.SHA384`, and
+            :class:`~cryptography.hazmat.primitives.hashes.SHA512` are allowed.
+
+        :param cert_status: An item from the
+            :class:`~cryptography.x509.ocsp.OCSPCertStatus` enumeration.
+
+        :param this_update: A naïve :class:`datetime.datetime` object
+            representing the most recent time in UTC at which the status being
+            indicated is known by the responder to be correct.
+
+        :param next_update: A naïve :class:`datetime.datetime` object or
+            ``None``. The time in UTC at or before which newer information will
+            be available about the status of the certificate.
+
+        :param revocation_time: A naïve :class:`datetime.datetime` object or
+            ``None`` if the ``cert`` is not revoked. The time in UTC at which
+            the certificate was revoked.
+
+        :param revocation_reason: An item from the
+            :class:`~cryptography.x509.ReasonFlags` enumeration or ``None`` if
+            the ``cert`` is not revoked.
+
+    .. method:: certificates(certs)
+
+        Add additional certificates that should be used to verify the
+        signature on the response. This is typically used when the responder
+        utilizes an OCSP delegate.
+
+        :param list certs: A list of :class:`~cryptography.x509.Certificate`
+            objects.
+
+    .. method:: responder_id(encoding, responder_cert)
+
+        Set the ``responderID`` on the OCSP response. This is the data a
+        client will use to determine what certificate signed the response.
+
+        :param responder_cert: The :class:`~cryptography.x509.Certificate`
+            object for the certificate whose private key will sign the
+            OCSP response. If the certificate and key do not match an
+            error will be raised when calling ``sign``.
+        :param encoding: Either
+            :attr:`~cryptography.x509.ocsp.OCSPResponderEncoding.HASH` or
+            :attr:`~cryptography.x509.ocsp.OCSPResponderEncoding.NAME`.
+
+    .. method:: add_extension(extension, critical)
+
+        Adds an extension to the response.
+
+        :param extension: An extension conforming to the
+            :class:`~cryptography.x509.ExtensionType` interface.
+
+        :param critical: Set to ``True`` if the extension must be understood and
+             handled.
+
+    .. method:: sign(private_key, algorithm)
+
+        Creates the OCSP response that can then be serialized and sent to
+        clients. This method will create a
+        :attr:`~cryptography.x509.ocsp.OCSPResponseStatus.SUCCESSFUL` response.
+
+        :param private_key: The
+            :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKey`
+            or
+            :class:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKey`
+            that will be used to sign the certificate.
+
+        :param algorithm: The
+            :class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm` that
+            will be used to generate the signature.
+
+        :returns: A new :class:`~cryptography.x509.ocsp.OCSPResponse`.
+
+    .. doctest::
+
+        >>> import datetime
+        >>> from cryptography.hazmat.backends import default_backend
+        >>> from cryptography.hazmat.primitives import hashes, serialization
+        >>> from cryptography.x509 import load_pem_x509_certificate, ocsp
+        >>> cert = load_pem_x509_certificate(pem_cert, default_backend())
+        >>> issuer = load_pem_x509_certificate(pem_issuer, default_backend())
+        >>> responder_cert = load_pem_x509_certificate(pem_responder_cert, default_backend())
+        >>> responder_key = serialization.load_pem_private_key(pem_responder_key, None, default_backend())
+        >>> builder = ocsp.OCSPResponseBuilder()
+        >>> # SHA1 is in this example because RFC 5019 mandates its use.
+        >>> builder = builder.add_response(
+        ...     cert=cert, issuer=issuer, algorithm=hashes.SHA1(),
+        ...     cert_status=ocsp.OCSPCertStatus.GOOD,
+        ...     this_update=datetime.datetime.now(),
+        ...     next_update=datetime.datetime.now(),
+        ...     revocation_time=None, revocation_reason=None
+        ... ).responder_id(
+        ...     ocsp.OCSPResponderEncoding.HASH, responder_cert
+        ... )
+        >>> response = builder.sign(responder_key, hashes.SHA256())
+        >>> response.certificate_status
+        <OCSPCertStatus.GOOD: 0>
+
+    .. classmethod:: build_unsuccessful(response_status)
+
+        Creates an unsigned OCSP response which can then be serialized and
+        sent to clients. ``build_unsuccessful`` may only be called with a
+        :class:`~cryptography.x509.ocsp.OCSPResponseStatus` that is not
+        ``SUCCESSFUL``. Since this is a class method note that no other
+        methods can or should be called as unsuccessful statuses do not
+        encode additional data.
+
+        :returns: A new :class:`~cryptography.x509.ocsp.OCSPResponse`.
+
+    .. doctest::
+
+        >>> from cryptography.hazmat.backends import default_backend
+        >>> from cryptography.hazmat.primitives import hashes, serialization
+        >>> from cryptography.x509 import load_pem_x509_certificate, ocsp
+        >>> response = ocsp.OCSPResponseBuilder.build_unsuccessful(
+        ...     ocsp.OCSPResponseStatus.UNAUTHORIZED
+        ... )
+        >>> response.response_status
+        <OCSPResponseStatus.UNAUTHORIZED: 6>
+
+
 Interfaces
 ~~~~~~~~~~
 
@@ -472,3 +640,20 @@ Interfaces
     .. attribute:: UNKNOWN
 
         The certificate being checked is not known to the OCSP responder.
+
+.. class:: OCSPResponderEncoding
+
+    .. versionadded:: 2.4
+
+    An enumeration of ``responderID`` encodings that can be passed to
+    :meth:`~cryptography.x509.ocsp.OCSPResponseBuilder.responder_id`.
+
+    .. attribute:: HASH
+
+        Encode the hash of the public key whose corresponding private key
+        signed the response.
+
+    .. attribute:: NAME
+
+        Encode the X.509 ``Name`` of the certificate whose private key signed
+        the response.
diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index 11d24b12..bd414fde 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -25,7 +25,9 @@ from cryptography.hazmat.backends.interfaces import (
 from cryptography.hazmat.backends.openssl import aead
 from cryptography.hazmat.backends.openssl.ciphers import _CipherContext
 from cryptography.hazmat.backends.openssl.cmac import _CMACContext
-from cryptography.hazmat.backends.openssl.decode_asn1 import _Integers
+from cryptography.hazmat.backends.openssl.decode_asn1 import (
+    _CRL_ENTRY_REASON_ENUM_TO_CODE, _Integers
+)
 from cryptography.hazmat.backends.openssl.dh import (
     _DHParameters, _DHPrivateKey, _DHPublicKey, _dh_params_dup
 )
@@ -38,6 +40,7 @@ from cryptography.hazmat.backends.openssl.ec import (
 from cryptography.hazmat.backends.openssl.encode_asn1 import (
     _CRL_ENTRY_EXTENSION_ENCODE_HANDLERS,
     _CRL_EXTENSION_ENCODE_HANDLERS, _EXTENSION_ENCODE_HANDLERS,
+    _OCSP_BASICRESP_EXTENSION_ENCODE_HANDLERS,
     _OCSP_REQUEST_EXTENSION_ENCODE_HANDLERS,
     _encode_asn1_int_gc, _encode_asn1_str_gc, _encode_name_gc, _txt2obj_gc,
 )
@@ -69,6 +72,7 @@ from cryptography.hazmat.primitives.ciphers.modes import (
     CBC, CFB, CFB8, CTR, ECB, GCM, OFB, XTS
 )
 from cryptography.hazmat.primitives.kdf import scrypt
+from cryptography.x509 import ocsp
 
 
 _MemoryBIO = collections.namedtuple("_MemoryBIO", ["bio", "char_ptr"])
@@ -1466,6 +1470,104 @@ class Backend(object):
         )
         return _OCSPRequest(self, ocsp_req)
 
+    def _create_ocsp_basic_response(self, builder, private_key, algorithm):
+        basic = self._lib.OCSP_BASICRESP_new()
+        self.openssl_assert(basic != self._ffi.NULL)
+        basic = self._ffi.gc(basic, self._lib.OCSP_BASICRESP_free)
+        evp_md = self._lib.EVP_get_digestbyname(
+            builder._response._algorithm.name.encode("ascii")
+        )
+        self.openssl_assert(evp_md != self._ffi.NULL)
+        certid = self._lib.OCSP_cert_to_id(
+            evp_md, builder._response._cert._x509,
+            builder._response._issuer._x509
+        )
+        self.openssl_assert(certid != self._ffi.NULL)
+        certid = self._ffi.gc(certid, self._lib.OCSP_CERTID_free)
+        if builder._response._revocation_reason is None:
+            reason = -1
+        else:
+            reason = _CRL_ENTRY_REASON_ENUM_TO_CODE[
+                builder._response._revocation_reason
+            ]
+        if builder._response._revocation_time is None:
+            rev_time = self._ffi.NULL
+        else:
+            rev_time = self._create_asn1_time(
+                builder._response._revocation_time
+            )
+
+        next_update = self._ffi.NULL
+        if builder._response._next_update is not None:
+            next_update = self._create_asn1_time(
+                builder._response._next_update
+            )
+
+        this_update = self._create_asn1_time(builder._response._this_update)
+
+        res = self._lib.OCSP_basic_add1_status(
+            basic,
+            certid,
+            builder._response._cert_status.value,
+            reason,
+            rev_time,
+            this_update,
+            next_update
+        )
+        self.openssl_assert(res != self._ffi.NULL)
+        # okay, now sign the basic structure
+        evp_md = self._lib.EVP_get_digestbyname(algorithm.name.encode("ascii"))
+        self.openssl_assert(evp_md != self._ffi.NULL)
+        responder_cert, responder_encoding = builder._responder_id
+        flags = self._lib.OCSP_NOCERTS
+        if responder_encoding is ocsp.OCSPResponderEncoding.HASH:
+            flags |= self._lib.OCSP_RESPID_KEY
+
+        if builder._certs is not None:
+            for cert in builder._certs:
+                res = self._lib.OCSP_basic_add1_cert(basic, cert._x509)
+                self.openssl_assert(res == 1)
+
+        self._create_x509_extensions(
+            extensions=builder._extensions,
+            handlers=_OCSP_BASICRESP_EXTENSION_ENCODE_HANDLERS,
+            x509_obj=basic,
+            add_func=self._lib.OCSP_BASICRESP_add_ext,
+            gc=True,
+        )
+
+        res = self._lib.OCSP_basic_sign(
+            basic, responder_cert._x509, private_key._evp_pkey,
+            evp_md, self._ffi.NULL, flags
+        )
+        if res != 1:
+            errors = self._consume_errors()
+            self.openssl_assert(
+                errors[0]._lib_reason_match(
+                    self._lib.ERR_LIB_X509,
+                    self._lib.X509_R_KEY_VALUES_MISMATCH
+                )
+            )
+            raise ValueError("responder_cert must be signed by private_key")
+
+        return basic
+
+    def create_ocsp_response(self, response_status, builder, private_key,
+                             algorithm):
+        if response_status is ocsp.OCSPResponseStatus.SUCCESSFUL:
+            basic = self._create_ocsp_basic_response(
+                builder, private_key, algorithm
+            )
+        else:
+            basic = self._ffi.NULL
+
+        ocsp_resp = self._lib.OCSP_response_create(
+            response_status.value, basic
+        )
+        self.openssl_assert(ocsp_resp != self._ffi.NULL)
+        ocsp_resp = self._ffi.gc(ocsp_resp, self._lib.OCSP_RESPONSE_free)
+        return _OCSPResponse(self, ocsp_resp)
+
     def elliptic_curve_exchange_algorithm_supported(self, algorithm, curve):
         return (
             self.elliptic_curve_supported(curve) and
diff --git a/src/cryptography/hazmat/backends/openssl/encode_asn1.py b/src/cryptography/hazmat/backends/openssl/encode_asn1.py
index c8b41a81..6ff1a9a4 100644
--- a/src/cryptography/hazmat/backends/openssl/encode_asn1.py
+++ b/src/cryptography/hazmat/backends/openssl/encode_asn1.py
@@ -614,3 +614,7 @@ _CRL_ENTRY_EXTENSION_ENCODE_HANDLERS = {
 _OCSP_REQUEST_EXTENSION_ENCODE_HANDLERS = {
     OCSPExtensionOID.NONCE: _encode_nonce,
 }
+
+_OCSP_BASICRESP_EXTENSION_ENCODE_HANDLERS = {
+    OCSPExtensionOID.NONCE: _encode_nonce,
+}
diff --git a/src/cryptography/x509/ocsp.py b/src/cryptography/x509/ocsp.py
index c89f12ce..2b0b1dc3 100644
--- a/src/cryptography/x509/ocsp.py
+++ b/src/cryptography/x509/ocsp.py
@@ -5,13 +5,16 @@
 from __future__ import absolute_import, division, print_function
 
 import abc
+import datetime
 from enum import Enum
 
 import six
 
 from cryptography import x509
 from cryptography.hazmat.primitives import hashes
-from cryptography.x509.base import _reject_duplicate_extension
+from cryptography.x509.base import (
+    _UNIX_EPOCH, _convert_to_naive_utc_time, _reject_duplicate_extension
+)
 
 
 _OIDS_TO_HASH = {
@@ -23,6 +26,11 @@ _OIDS_TO_HASH = {
 }
 
 
+class OCSPResponderEncoding(Enum):
+    HASH = "By Hash"
+    NAME = "By Name"
+
+
 class OCSPResponseStatus(Enum):
     SUCCESSFUL = 0
     MALFORMED_REQUEST = 1
@@ -33,6 +41,17 @@ class OCSPResponseStatus(Enum):
 
 
 _RESPONSE_STATUS_TO_ENUM = dict((x.value, x) for x in OCSPResponseStatus)
+_ALLOWED_HASHES = (
+    hashes.SHA1, hashes.SHA224, hashes.SHA256,
+    hashes.SHA384, hashes.SHA512
+)
+
+
+def _verify_algorithm(algorithm):
+    if not isinstance(algorithm, _ALLOWED_HASHES):
+        raise ValueError(
+            "Algorithm must be SHA1, SHA224, SHA256, SHA384, or SHA512"
+        )
 
 
 class OCSPCertStatus(Enum):
@@ -63,14 +82,7 @@ class OCSPRequestBuilder(object):
         if self._request is not None:
             raise ValueError("Only one certificate can be added to a request")
 
-        allowed_hashes = (
-            hashes.SHA1, hashes.SHA224, hashes.SHA256,
-            hashes.SHA384, hashes.SHA512
-        )
-        if not isinstance(algorithm, allowed_hashes):
-            raise ValueError(
-                "Algorithm must be SHA1, SHA224, SHA256, SHA384, or SHA512"
-            )
+        _verify_algorithm(algorithm)
         if (
             not isinstance(cert, x509.Certificate) or
             not isinstance(issuer, x509.Certificate)
@@ -98,6 +110,157 @@ class OCSPRequestBuilder(object):
         return backend.create_ocsp_request(self)
 
 
+class _SingleResponse(object):
+    def __init__(self, cert, issuer, algorithm, cert_status, this_update,
+                 next_update, revocation_time, revocation_reason):
+        if (
+            not isinstance(cert, x509.Certificate) or
+            not isinstance(issuer, x509.Certificate)
+        ):
+            raise TypeError("cert and issuer must be a Certificate")
+
+        _verify_algorithm(algorithm)
+        if not isinstance(this_update, datetime.datetime):
+            raise TypeError("this_update must be a datetime object")
+        if (
+            next_update is not None and
+            not isinstance(next_update, datetime.datetime)
+        ):
+            raise TypeError("next_update must be a datetime object or None")
+
+        self._cert = cert
+        self._issuer = issuer
+        self._algorithm = algorithm
+        self._this_update = this_update
+        self._next_update = next_update
+
+        if not isinstance(cert_status, OCSPCertStatus):
+            raise TypeError(
+                "cert_status must be an item from the OCSPCertStatus enum"
+            )
+        if cert_status is not OCSPCertStatus.REVOKED:
+            if revocation_time is not None:
+                raise ValueError(
+                    "revocation_time can only be provided if the certificate "
+                    "is revoked"
+                )
+            if revocation_reason is not None:
+                raise ValueError(
+                    "revocation_reason can only be provided if the certificate"
+                    " is revoked"
+                )
+        else:
+            if not isinstance(revocation_time, datetime.datetime):
+                raise TypeError("revocation_time must be a datetime object")
+
+            revocation_time = _convert_to_naive_utc_time(revocation_time)
+            if revocation_time <= _UNIX_EPOCH:
+                raise ValueError('The revocation_time must be after the unix'
+                                 ' epoch (1970 January 1).')
+
+            if (
+                revocation_reason is not None and
+                not isinstance(revocation_reason, x509.ReasonFlags)
+            ):
+                raise TypeError(
+                    "revocation_reason must be an item from the ReasonFlags "
+                    "enum or None"
+                )
+
+        self._cert_status = cert_status
+        self._revocation_time = revocation_time
+        self._revocation_reason = revocation_reason
+
+
+class OCSPResponseBuilder(object):
+    def __init__(self, response=None, responder_id=None, certs=None,
+                 extensions=[]):
+        self._response = response
+        self._responder_id = responder_id
+        self._certs = certs
+        self._extensions = extensions
+
+    def add_response(self, cert, issuer, algorithm, cert_status, this_update,
+                     next_update, revocation_time, revocation_reason):
+        if self._response is not None:
+            raise ValueError("Only one response per OCSPResponse.")
+
+        singleresp = _SingleResponse(
+            cert, issuer, algorithm, cert_status, this_update, next_update,
+            revocation_time, revocation_reason
+        )
+        return OCSPResponseBuilder(
+            singleresp, self._responder_id,
+            self._certs, self._extensions,
+        )
+
+    def responder_id(self, encoding, responder_cert):
+        if self._responder_id is not None:
+            raise ValueError("responder_id can only be set once")
+        if not isinstance(responder_cert, x509.Certificate):
+            raise TypeError("responder_cert must be a Certificate")
+        if not isinstance(encoding, OCSPResponderEncoding):
+            raise TypeError(
+                "encoding must be an element from OCSPResponderEncoding"
+            )
+
+        return OCSPResponseBuilder(
+            self._response, (responder_cert, encoding),
+            self._certs, self._extensions,
+        )
+
+    def certificates(self, certs):
+        if self._certs is not None:
+            raise ValueError("certificates may only be set once")
+        certs = list(certs)
+        if len(certs) == 0:
+            raise ValueError("certs must not be an empty list")
+        if not all(isinstance(x, x509.Certificate) for x in certs):
+            raise TypeError("certs must be a list of Certificates")
+        return OCSPResponseBuilder(
+            self._response, self._responder_id,
+            certs, self._extensions,
+        )
+
+    def add_extension(self, extension, critical):
+        if not isinstance(extension, x509.ExtensionType):
+            raise TypeError("extension must be an ExtensionType")
+
+        extension = x509.Extension(extension.oid, critical, extension)
+        _reject_duplicate_extension(extension, self._extensions)
+
+        return OCSPResponseBuilder(
+            self._response, self._responder_id,
+            self._certs, self._extensions + [extension],
+        )
+
+    def sign(self, private_key, algorithm):
+        from cryptography.hazmat.backends.openssl.backend import backend
+        if self._response is None:
+            raise ValueError("You must add a response before signing")
+        if self._responder_id is None:
+            raise ValueError("You must add a responder_id before signing")
+
+        if not isinstance(algorithm, hashes.HashAlgorithm):
+            raise TypeError("Algorithm must be a registered hash algorithm.")
+
+        return backend.create_ocsp_response(
+            OCSPResponseStatus.SUCCESSFUL, self, private_key, algorithm
+        )
+
+    @classmethod
+    def build_unsuccessful(cls, response_status):
+        from cryptography.hazmat.backends.openssl.backend import backend
+        if not isinstance(response_status, OCSPResponseStatus):
+            raise TypeError(
+                "response_status must be an item from OCSPResponseStatus"
+            )
+        if response_status is OCSPResponseStatus.SUCCESSFUL:
+            raise ValueError("response_status cannot be SUCCESSFUL")
+
+        return backend.create_ocsp_response(response_status, None, None, None)
+
+
 @six.add_metaclass(abc.ABCMeta)
 class OCSPRequest(object):
     @abc.abstractproperty
diff --git a/tests/x509/test_ocsp.py b/tests/x509/test_ocsp.py
index 3ee6a26e..fad48dab 100644
--- a/tests/x509/test_ocsp.py
+++ b/tests/x509/test_ocsp.py
@@ -13,10 +13,12 @@ import pytest
 from cryptography import x509
 from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.primitives import hashes, serialization
+from cryptography.hazmat.primitives.asymmetric import ec
 from cryptography.hazmat.primitives.asymmetric.padding import PKCS1v15
 from cryptography.x509 import ocsp
 
 from .test_x509 import _load_cert
+from ..hazmat.primitives.fixtures_ec import EC_KEY_SECP256R1
 from ..utils import load_vectors_from_file
 
 
@@ -43,6 +45,33 @@ def _cert_and_issuer():
     return cert, issuer
 
 
+def _generate_root():
+    from cryptography.hazmat.backends.openssl.backend import backend
+
+    private_key = EC_KEY_SECP256R1.private_key(backend)
+    subject = x509.Name([
+        x509.NameAttribute(x509.NameOID.COUNTRY_NAME, u'US'),
+        x509.NameAttribute(x509.NameOID.COMMON_NAME, u'Cryptography CA'),
+    ])
+
+    builder = x509.CertificateBuilder().serial_number(
+        123456789
+    ).issuer_name(
+        subject
+    ).subject_name(
+        subject
+    ).public_key(
+        private_key.public_key()
+    ).not_valid_before(
+        datetime.datetime.now()
+    ).not_valid_after(
+        datetime.datetime.now() + datetime.timedelta(days=3650)
+    )
+
+    cert = builder.sign(private_key, hashes.SHA256(), backend)
+    return cert, private_key
+
+
 class TestOCSPRequest(object):
     def test_bad_request(self):
         with pytest.raises(ValueError):
@@ -182,6 +211,359 @@ class TestOCSPRequestBuilder(object):
         assert req.extensions[0].critical is critical
 
 
+class TestOCSPResponseBuilder(object):
+    def test_add_response_twice(self):
+        cert, issuer = _cert_and_issuer()
+        time = datetime.datetime.now()
+        builder = ocsp.OCSPResponseBuilder()
+        builder = builder.add_response(
+            cert, issuer, hashes.SHA256(), ocsp.OCSPCertStatus.GOOD, time,
+            time, None, None
+        )
+        with pytest.raises(ValueError):
+            builder.add_response(
+                cert, issuer, hashes.SHA256(), ocsp.OCSPCertStatus.GOOD, time,
+                time, None, None
+            )
+
+    def test_invalid_add_response(self):
+        cert, issuer = _cert_and_issuer()
+        time = datetime.datetime.utcnow()
+        reason = x509.ReasonFlags.cessation_of_operation
+        builder = ocsp.OCSPResponseBuilder()
+        with pytest.raises(TypeError):
+            builder.add_response(
+                'bad', issuer, hashes.SHA256(), ocsp.OCSPCertStatus.GOOD,
+                time, time, None, None
+            )
+        with pytest.raises(TypeError):
+            builder.add_response(
+                cert, 'bad', hashes.SHA256(), ocsp.OCSPCertStatus.GOOD,
+                time, time, None, None
+            )
+        with pytest.raises(ValueError):
+            builder.add_response(
+                cert, issuer, 'notahash', ocsp.OCSPCertStatus.GOOD,
+                time, time, None, None
+            )
+        with pytest.raises(TypeError):
+            builder.add_response(
+                cert, issuer, hashes.SHA256(), ocsp.OCSPCertStatus.GOOD,
+                'bad', time, None, None
+            )
+        with pytest.raises(TypeError):
+            builder.add_response(
+                cert, issuer, hashes.SHA256(), ocsp.OCSPCertStatus.GOOD,
+                time, 'bad', None, None
+            )
+
+        with pytest.raises(TypeError):
+            builder.add_response(
+                cert, issuer, hashes.SHA256(), 0, time, time, None, None
+            )
+        with pytest.raises(ValueError):
+            builder.add_response(
+                cert, issuer, hashes.SHA256(), ocsp.OCSPCertStatus.GOOD,
+                time, time, time, None
+            )
+        with pytest.raises(ValueError):
+            builder.add_response(
+                cert, issuer, hashes.SHA256(), ocsp.OCSPCertStatus.GOOD,
+                time, time, None, reason
+            )
+        with pytest.raises(TypeError):
+            builder.add_response(
+                cert, issuer, hashes.SHA256(), ocsp.OCSPCertStatus.REVOKED,
+                time, time, None, reason
+            )
+        with pytest.raises(TypeError):
+            builder.add_response(
+                cert, issuer, hashes.SHA256(), ocsp.OCSPCertStatus.REVOKED,
+                time, time, time, 0
+            )
+        with pytest.raises(ValueError):
+            builder.add_response(
+                cert, issuer, hashes.SHA256(), ocsp.OCSPCertStatus.REVOKED,
+                time, time, time - datetime.timedelta(days=36500), None
+            )
+
+    def test_invalid_certificates(self):
+        builder = ocsp.OCSPResponseBuilder()
+        with pytest.raises(ValueError):
+            builder.certificates([])
+        with pytest.raises(TypeError):
+            builder.certificates(['notacert'])
+        with pytest.raises(TypeError):
+            builder.certificates('invalid')
+
+        _, issuer = _cert_and_issuer()
+        builder = builder.certificates([issuer])
+        with pytest.raises(ValueError):
+            builder.certificates([issuer])
+
+    def test_invalid_responder_id(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, _ = _cert_and_issuer()
+        with pytest.raises(TypeError):
+            builder.responder_id(ocsp.OCSPResponderEncoding.HASH, 'invalid')
+        with pytest.raises(TypeError):
+            builder.responder_id('notanenum', cert)
+
+        builder = builder.responder_id(ocsp.OCSPResponderEncoding.NAME, cert)
+        with pytest.raises(ValueError):
+            builder.responder_id(ocsp.OCSPResponderEncoding.NAME, cert)
+
+    def test_invalid_extension(self):
+        builder = ocsp.OCSPResponseBuilder()
+        with pytest.raises(TypeError):
+            builder.add_extension("notanextension", True)
+
+    def test_sign_no_response(self):
+        builder = ocsp.OCSPResponseBuilder()
+        root_cert, private_key = _generate_root()
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.NAME, root_cert
+        )
+        with pytest.raises(ValueError):
+            builder.sign(private_key, hashes.SHA256())
+
+    def test_sign_no_responder_id(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        _, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        next_update = this_update + datetime.timedelta(days=7)
+        builder = builder.add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.GOOD, this_update,
+            next_update, None, None
+        )
+        with pytest.raises(ValueError):
+            builder.sign(private_key, hashes.SHA256())
+
+    def test_sign_invalid_hash_algorithm(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        root_cert, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        next_update = this_update + datetime.timedelta(days=7)
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.NAME, root_cert
+        ).add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.GOOD, this_update,
+            next_update, None, None
+        )
+        with pytest.raises(TypeError):
+            builder.sign(private_key, 'notahash')
+
+    def test_sign_good_cert(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        root_cert, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        next_update = this_update + datetime.timedelta(days=7)
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.NAME, root_cert
+        ).add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.GOOD, this_update,
+            next_update, None, None
+        )
+        resp = builder.sign(private_key, hashes.SHA256())
+        assert resp.responder_name == root_cert.subject
+        assert resp.responder_key_hash is None
+        assert (current_time - resp.produced_at).total_seconds() < 10
+        assert (resp.signature_algorithm_oid ==
+                x509.SignatureAlgorithmOID.ECDSA_WITH_SHA256)
+        assert resp.certificate_status == ocsp.OCSPCertStatus.GOOD
+        assert resp.revocation_time is None
+        assert resp.revocation_reason is None
+        assert resp.this_update == this_update
+        assert resp.next_update == next_update
+        private_key.public_key().verify(
+            resp.signature, resp.tbs_response_bytes, ec.ECDSA(hashes.SHA256())
+        )
+
+    def test_sign_revoked_cert(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        root_cert, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        next_update = this_update + datetime.timedelta(days=7)
+        revoked_date = this_update - datetime.timedelta(days=300)
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.NAME, root_cert
+        ).add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.REVOKED,
+            this_update, next_update, revoked_date, None
+        )
+        resp = builder.sign(private_key, hashes.SHA256())
+        assert resp.certificate_status == ocsp.OCSPCertStatus.REVOKED
+        assert resp.revocation_time == revoked_date
+        assert resp.revocation_reason is None
+        assert resp.this_update == this_update
+        assert resp.next_update == next_update
+        private_key.public_key().verify(
+            resp.signature, resp.tbs_response_bytes, ec.ECDSA(hashes.SHA256())
+        )
+
+    def test_sign_with_appended_certs(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        root_cert, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        next_update = this_update + datetime.timedelta(days=7)
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.NAME, root_cert
+        ).add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.GOOD, this_update,
+            next_update, None, None
+        ).certificates(
+            [root_cert]
+        )
+        resp = builder.sign(private_key, hashes.SHA256())
+        assert resp.certificates == [root_cert]
+
+    def test_sign_revoked_no_next_update(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        root_cert, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        revoked_date = this_update - datetime.timedelta(days=300)
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.NAME, root_cert
+        ).add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.REVOKED,
+            this_update, None, revoked_date, None
+        )
+        resp = builder.sign(private_key, hashes.SHA256())
+        assert resp.certificate_status == ocsp.OCSPCertStatus.REVOKED
+        assert resp.revocation_time == revoked_date
+        assert resp.revocation_reason is None
+        assert resp.this_update == this_update
+        assert resp.next_update is None
+        private_key.public_key().verify(
+            resp.signature, resp.tbs_response_bytes, ec.ECDSA(hashes.SHA256())
+        )
+
+    def test_sign_revoked_with_reason(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        root_cert, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        next_update = this_update + datetime.timedelta(days=7)
+        revoked_date = this_update - datetime.timedelta(days=300)
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.NAME, root_cert
+        ).add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.REVOKED,
+            this_update, next_update, revoked_date,
+            x509.ReasonFlags.key_compromise
+        )
+        resp = builder.sign(private_key, hashes.SHA256())
+        assert resp.certificate_status == ocsp.OCSPCertStatus.REVOKED
+        assert resp.revocation_time == revoked_date
+        assert resp.revocation_reason is x509.ReasonFlags.key_compromise
+        assert resp.this_update == this_update
+        assert resp.next_update == next_update
+        private_key.public_key().verify(
+            resp.signature, resp.tbs_response_bytes, ec.ECDSA(hashes.SHA256())
+        )
+
+    def test_sign_responder_id_key_hash(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        root_cert, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        next_update = this_update + datetime.timedelta(days=7)
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.HASH, root_cert
+        ).add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.GOOD, this_update,
+            next_update, None, None
+        )
+        resp = builder.sign(private_key, hashes.SHA256())
+        assert resp.responder_name is None
+        assert resp.responder_key_hash == (
+            b'\x8ca\x94\xe0\x948\xed\x89\xd8\xd4N\x89p\t\xd6\xf9^_\xec}'
+        )
+        private_key.public_key().verify(
+            resp.signature, resp.tbs_response_bytes, ec.ECDSA(hashes.SHA256())
+        )
+
+    def test_invalid_sign_responder_cert_does_not_match_private_key(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        root_cert, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        next_update = this_update + datetime.timedelta(days=7)
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.HASH, root_cert
+        ).add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.GOOD, this_update,
+            next_update, None, None
+        )
+        from cryptography.hazmat.backends.openssl.backend import backend
+        diff_key = ec.generate_private_key(ec.SECP256R1(), backend)
+        with pytest.raises(ValueError):
+            builder.sign(diff_key, hashes.SHA256())
+
+    def test_sign_with_extension(self):
+        builder = ocsp.OCSPResponseBuilder()
+        cert, issuer = _cert_and_issuer()
+        root_cert, private_key = _generate_root()
+        current_time = datetime.datetime.utcnow().replace(microsecond=0)
+        this_update = current_time - datetime.timedelta(days=1)
+        next_update = this_update + datetime.timedelta(days=7)
+        builder = builder.responder_id(
+            ocsp.OCSPResponderEncoding.HASH, root_cert
+        ).add_response(
+            cert, issuer, hashes.SHA1(), ocsp.OCSPCertStatus.GOOD, this_update,
+            next_update, None, None
+        ).add_extension(
+            x509.OCSPNonce(b"012345"), False
+        )
+        resp = builder.sign(private_key, hashes.SHA256())
+        assert len(resp.extensions) == 1
+        assert resp.extensions[0].value == x509.OCSPNonce(b"012345")
+        assert resp.extensions[0].critical is False
+        private_key.public_key().verify(
+            resp.signature, resp.tbs_response_bytes, ec.ECDSA(hashes.SHA256())
+        )
+
+    @pytest.mark.parametrize(
+        ("status", "der"),
+        [
+            (ocsp.OCSPResponseStatus.MALFORMED_REQUEST, b"0\x03\n\x01\x01"),
+            (ocsp.OCSPResponseStatus.INTERNAL_ERROR, b"0\x03\n\x01\x02"),
+            (ocsp.OCSPResponseStatus.TRY_LATER, b"0\x03\n\x01\x03"),
+            (ocsp.OCSPResponseStatus.SIG_REQUIRED, b"0\x03\n\x01\x05"),
+            (ocsp.OCSPResponseStatus.UNAUTHORIZED, b"0\x03\n\x01\x06"),
+        ]
+    )
+    def test_build_non_successful_statuses(self, status, der):
+        resp = ocsp.OCSPResponseBuilder.build_unsuccessful(status)
+        assert resp.response_status is status
+        assert resp.public_bytes(serialization.Encoding.DER) == der
+
+    def test_invalid_build_not_a_status(self):
+        with pytest.raises(TypeError):
+            ocsp.OCSPResponseBuilder.build_unsuccessful("notastatus")
+
+    def test_invalid_build_successful_status(self):
+        with pytest.raises(ValueError):
+            ocsp.OCSPResponseBuilder.build_unsuccessful(
+                ocsp.OCSPResponseStatus.SUCCESSFUL
+            )
+
+
 class TestOCSPResponse(object):
     def test_bad_response(self):
         with pytest.raises(ValueError):