diff --git a/acme/client.py b/acme/client.py
index 43c659bb8..f5a651652 100644
--- a/acme/client.py
+++ b/acme/client.py
@@ -540,21 +540,17 @@ class Client(object):  # pylint: disable=too-many-instance-attributes
         else:
             return None
 
-    def revoke(self, certr, when=messages.Revocation.NOW):
+    def revoke(self, cert):
         """Revoke certificate.
 
-        :param certr: Certificate Resource
-        :type certr: `.CertificateResource`
-
-        :param when: When should the revocation take place? Takes
-           the same values as `.messages.Revocation.revoke`.
+        :param .ComparableX509 cert: `M2Crypto.X509.X509` wrapped in
+            `.ComparableX509`
 
         :raises .ClientError: If revocation is unsuccessful.
 
         """
-        rev = messages.Revocation(revoke=when, authorizations=tuple(
-            authzr.uri for authzr in certr.authzrs))
-        response = self._post(certr.uri, rev)
+        response = self._post(messages.Revocation.url(self.new_reg_uri),
+                              messages.Revocation(certificate=cert))
         if response.status_code != httplib.OK:
             raise errors.ClientError(
                 'Successful revocation must return HTTP OK status')
diff --git a/acme/client_test.py b/acme/client_test.py
index 7f09f8bdf..d408f0564 100644
--- a/acme/client_test.py
+++ b/acme/client_test.py
@@ -509,8 +509,9 @@ class ClientTest(unittest.TestCase):
 
     def test_revoke(self):
         self._mock_post_get()
-        self.net.revoke(self.certr, when=messages.Revocation.NOW)
-        self.post.assert_called_once_with(self.certr.uri, mock.ANY)
+        self.net.revoke(self.certr.body)
+        self.post.assert_called_once_with(messages.Revocation.url(
+            self.net.new_reg_uri), mock.ANY)
 
     def test_revoke_bad_status_raises_error(self):
         self.response.status_code = httplib.METHOD_NOT_ALLOWED
diff --git a/acme/messages.py b/acme/messages.py
index e355e9fd0..cd5a65f79 100644
--- a/acme/messages.py
+++ b/acme/messages.py
@@ -1,4 +1,6 @@
 """ACME protocol messages."""
+import urlparse
+
 from acme import challenges
 from acme import fields
 from acme import jose
@@ -327,28 +329,22 @@ class CertificateResource(ResourceWithURI):
 class Revocation(jose.JSONObjectWithFields):
     """Revocation message.
 
-    :ivar revoke: Either a `datetime.datetime` or `Revocation.NOW`.
-    :ivar tuple authorizations: Same as `CertificateRequest.authorizations`
+    :ivar .ComparableX509 certificate: `M2Crypto.X509.X509` wrapped in
+        `.ComparableX509`
 
     """
+    certificate = jose.Field(
+        'certificate', decoder=jose.decode_cert, encoder=jose.encode_cert)
 
-    NOW = 'now'
-    """A possible value for `revoke`, denoting that certificate should
-    be revoked now."""
+    # TODO: acme-spec#138, this allows only one ACME server instance per domain
+    PATH = '/acme/revoke-cert'
+    """Path to revocation URL, see `url`"""
 
-    revoke = jose.Field('revoke')
-    authorizations = CertificateRequest._fields['authorizations']
+    @classmethod
+    def url(cls, base):
+        """Get revocation URL.
 
-    @revoke.decoder
-    def revoke(value):  # pylint: disable=missing-docstring,no-self-argument
-        if value == Revocation.NOW:
-            return value
-        else:
-            return fields.RFC3339Field.default_decoder(value)
+        :param str base: New Registration Resource or server (root) URL.
 
-    @revoke.encoder
-    def revoke(value):  # pylint: disable=missing-docstring,no-self-argument
-        if value == Revocation.NOW:
-            return value
-        else:
-            return fields.RFC3339Field.default_encoder(value)
+        """
+        return urlparse.urljoin(base, cls.PATH)
diff --git a/acme/messages_test.py b/acme/messages_test.py
index 6749f55dc..9b3c03fbc 100644
--- a/acme/messages_test.py
+++ b/acme/messages_test.py
@@ -1,5 +1,4 @@
 """Tests for acme.messages."""
-import datetime
 import os
 import pkg_resources
 import unittest
@@ -7,7 +6,6 @@ import unittest
 from Crypto.PublicKey import RSA
 import M2Crypto
 import mock
-import pytz
 
 from acme import challenges
 from acme import jose
@@ -23,6 +21,9 @@ CSR = jose.ComparableX509(M2Crypto.X509.load_request_string(
     M2Crypto.X509.FORMAT_DER))
 KEY = jose.util.HashableRSAKey(RSA.importKey(pkg_resources.resource_string(
     'acme.jose', os.path.join('testdata', 'rsa512_key.pem'))))
+CERT = jose.ComparableX509(M2Crypto.X509.load_cert(
+    format=M2Crypto.X509.FORMAT_DER, file=pkg_resources.resource_filename(
+        'acme.jose', os.path.join('testdata', 'cert.der'))))
 
 
 class ErrorTest(unittest.TestCase):
@@ -318,27 +319,20 @@ class CertificateResourceTest(unittest.TestCase):
 class RevocationTest(unittest.TestCase):
     """Tests for acme.messages.RevocationTest."""
 
+    def test_url(self):
+        from acme.messages import Revocation
+        url = 'https://letsencrypt-demo.org/acme/revoke-cert'
+        self.assertEqual(url, Revocation.url('https://letsencrypt-demo.org'))
+        self.assertEqual(
+            url, Revocation.url('https://letsencrypt-demo.org/acme/new-reg'))
+
     def setUp(self):
         from acme.messages import Revocation
-        self.rev_now = Revocation(authorizations=(), revoke=Revocation.NOW)
-        self.rev_date = Revocation(authorizations=(), revoke=datetime.datetime(
-            2015, 3, 27, tzinfo=pytz.utc))
-        self.jobj_now = {'authorizations': (), 'revoke': Revocation.NOW}
-        self.jobj_date = {'authorizations': (),
-                          'revoke': '2015-03-27T00:00:00Z'}
-
-    def test_revoke_decoder(self):
-        from acme.messages import Revocation
-        self.assertEqual(self.rev_now, Revocation.from_json(self.jobj_now))
-        self.assertEqual(self.rev_date, Revocation.from_json(self.jobj_date))
-
-    def test_revoke_encoder(self):
-        self.assertEqual(self.jobj_now, self.rev_now.to_partial_json())
-        self.assertEqual(self.jobj_date, self.rev_date.to_partial_json())
+        self.rev = Revocation(certificate=CERT)
 
     def test_from_json_hashable(self):
         from acme.messages import Revocation
-        hash(Revocation.from_json(self.rev_now.to_json()))
+        hash(Revocation.from_json(self.rev.to_json()))
 
 
 if __name__ == '__main__':
diff --git a/letsencrypt/constants.py b/letsencrypt/constants.py
index 47539615d..356b8ed14 100644
--- a/letsencrypt/constants.py
+++ b/letsencrypt/constants.py
@@ -81,7 +81,3 @@ ACCOUNT_KEYS_DIR = "keys"
 REC_TOKEN_DIR = "recovery_tokens"
 """Directory where all recovery tokens are saved (relative to
 IConfig.work_dir)."""
-
-NETSTAT = "/bin/netstat"
-"""Location of netstat binary for checking whether a listener is already
-running on the specified port (Linux-specific)."""
diff --git a/letsencrypt/interfaces.py b/letsencrypt/interfaces.py
index c0d44a134..d2a420d00 100644
--- a/letsencrypt/interfaces.py
+++ b/letsencrypt/interfaces.py
@@ -148,8 +148,7 @@ class IConfig(zope.interface.Interface):
 
     """
     server = zope.interface.Attribute(
-        "CA hostname (and optionally :port). The server certificate must "
-        "be trusted in order to avoid further modifications to the client.")
+        "ACME new registration URI (including /acme/new-reg).")
     email = zope.interface.Attribute(
         "Email used for registration and recovery contact.")
     rsa_key_size = zope.interface.Attribute("Size of the RSA key.")
diff --git a/letsencrypt/revoker.py b/letsencrypt/revoker.py
index 0d3bd8e79..402157721 100644
--- a/letsencrypt/revoker.py
+++ b/letsencrypt/revoker.py
@@ -253,7 +253,7 @@ class Revoker(object):
             raise errors.LetsEncryptRevokerError(
                 "Corrupted backup key file: %s" % cert.backup_key_path)
 
-        return self.network.revoke(certr=None)  # XXX
+        return self.network.revoke(cert=None)  # XXX
 
     def _remove_certs_keys(self, cert_list):  # pylint: disable=no-self-use
         """Remove certificate and key.