diff --git a/stix2/test/v20/test_markings.py b/stix2/test/v20/test_markings.py
index c461e23..d3a3a1f 100644
--- a/stix2/test/v20/test_markings.py
+++ b/stix2/test/v20/test_markings.py
@@ -194,14 +194,14 @@ def test_registered_custom_marking():
     nm = NewMarking(property1='something', property2=55)
 
     marking_def = stix2.v20.MarkingDefinition(
-        id="marking-definition--00000000-0000-0000-0000-000000000012",
+        id="marking-definition--00000000-0000-4000-8000-000000000012",
         created="2017-01-22T00:00:00.000Z",
         definition_type="x-new-marking-type",
         definition=nm
     )
 
     assert marking_def.type == "marking-definition"
-    assert marking_def.id == "marking-definition--00000000-0000-0000-0000-000000000012"
+    assert marking_def.id == "marking-definition--00000000-0000-4000-8000-000000000012"
     assert marking_def.created == dt.datetime(2017, 1, 22, 0, 0, 0, tzinfo=pytz.utc)
     assert marking_def.definition.property1 == "something"
     assert marking_def.definition.property2 == 55
@@ -229,7 +229,7 @@ def test_not_registered_marking_raises_exception():
         no = NewObject2(property1='something', property2=55)
 
         stix2.v20.MarkingDefinition(
-            id="marking-definition--00000000-0000-0000-0000-000000000012",
+            id="marking-definition--00000000-0000-4000-8000-000000000012",
             created="2017-01-22T00:00:00.000Z",
             definition_type="x-new-marking-type2",
             definition=no
diff --git a/stix2/test/v21/conftest.py b/stix2/test/v21/conftest.py
index 2c7f641..60633ec 100644
--- a/stix2/test/v21/conftest.py
+++ b/stix2/test/v21/conftest.py
@@ -27,7 +27,7 @@ def uuid4(monkeypatch):
 
         def wrapped():
             data[0] += 1
-            return "00000000-0000-0000-0000-00000000%04x" % data[0]
+            return "00000000-0000-4000-8000-00000000%04x" % data[0]
 
         return wrapped
     monkeypatch.setattr(uuid, "uuid4", wrapper())
@@ -52,7 +52,7 @@ def relationship(uuid4, clock):
 def stix_objs1():
     ind1 = {
         "created": "2017-01-27T13:49:53.935Z",
-        "id": "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+        "id": "indicator--00000000-0000-4000-8000-000000000001",
         "labels": [
             "url-watchlist"
         ],
@@ -65,7 +65,7 @@ def stix_objs1():
     }
     ind2 = {
         "created": "2017-01-27T13:49:53.935Z",
-        "id": "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+        "id": "indicator--00000000-0000-4000-8000-000000000001",
         "labels": [
             "url-watchlist"
         ],
@@ -78,7 +78,7 @@ def stix_objs1():
     }
     ind3 = {
         "created": "2017-01-27T13:49:53.935Z",
-        "id": "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+        "id": "indicator--00000000-0000-4000-8000-000000000001",
         "labels": [
             "url-watchlist"
         ],
@@ -91,7 +91,7 @@ def stix_objs1():
     }
     ind4 = {
         "created": "2017-01-27T13:49:53.935Z",
-        "id": "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f",
+        "id": "indicator--00000000-0000-4000-8000-000000000002",
         "labels": [
             "url-watchlist"
         ],
@@ -104,7 +104,7 @@ def stix_objs1():
     }
     ind5 = {
         "created": "2017-01-27T13:49:53.935Z",
-        "id": "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f",
+        "id": "indicator--00000000-0000-4000-8000-000000000002",
         "labels": [
             "url-watchlist"
         ],
@@ -122,7 +122,7 @@ def stix_objs1():
 def stix_objs2():
     ind6 = {
         "created": "2017-01-27T13:49:53.935Z",
-        "id": "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+        "id": "indicator--00000000-0000-4000-8000-000000000001",
         "labels": [
             "url-watchlist"
         ],
@@ -135,7 +135,7 @@ def stix_objs2():
     }
     ind7 = {
         "created": "2017-01-27T13:49:53.935Z",
-        "id": "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f",
+        "id": "indicator--00000000-0000-4000-8000-000000000002",
         "labels": [
             "url-watchlist"
         ],
@@ -148,7 +148,7 @@ def stix_objs2():
     }
     ind8 = {
         "created": "2017-01-27T13:49:53.935Z",
-        "id": "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f",
+        "id": "indicator--00000000-0000-4000-8000-000000000002",
         "labels": [
             "url-watchlist"
         ],
diff --git a/stix2/test/v21/constants.py b/stix2/test/v21/constants.py
index c49629d..b095187 100644
--- a/stix2/test/v21/constants.py
+++ b/stix2/test/v21/constants.py
@@ -7,17 +7,17 @@ FAKE_TIME = dt.datetime(2017, 1, 1, 12, 34, 56, tzinfo=pytz.utc)
 ATTACK_PATTERN_ID = "attack-pattern--0c7b5b88-8ff7-4a4d-aa9d-feb398cd0061"
 CAMPAIGN_ID = "campaign--8e2e2d2b-17d4-4cbf-938f-98ee46b3cd3f"
 COURSE_OF_ACTION_ID = "course-of-action--8e2e2d2b-17d4-4cbf-938f-98ee46b3cd3f"
-IDENTITY_ID = "identity--311b2d2d-f010-5473-83ec-1edf84858f4c"
-INDICATOR_ID = "indicator--01234567-89ab-cdef-0123-456789abcdef"
+IDENTITY_ID = "identity--311b2d2d-f010-4473-83ec-1edf84858f4c"
+INDICATOR_ID = "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7"
 INTRUSION_SET_ID = "intrusion-set--4e78f46f-a023-4e5f-bc24-71b3ca22ec29"
 LOCATION_ID = "location--a6e9345f-5a15-4c29-8bb3-7dcc5d168d64"
-MALWARE_ID = "malware--fedcba98-7654-3210-fedc-ba9876543210"
+MALWARE_ID = "malware--9c4638ec-f1de-4ddb-abf4-1b760417654e"
 MARKING_DEFINITION_ID = "marking-definition--613f2e26-407d-48c7-9eca-b8e91df99dc9"
 NOTE_ID = "note--0c7b5b88-8ff7-4a4d-aa9d-feb398cd0061"
 OBSERVED_DATA_ID = "observed-data--b67d30ff-02ac-498a-92f9-32f845f448cf"
 OPINION_ID = "opinion--b01efc25-77b4-4003-b18b-f6e24b5cd9f7"
 REPORT_ID = "report--84e4d88f-44ea-4bcd-bbf3-b2c1c320bcb3"
-RELATIONSHIP_ID = "relationship--00000000-1111-2222-3333-444444444444"
+RELATIONSHIP_ID = "relationship--df7c87eb-75d2-4948-af81-9d49d246f301"
 THREAT_ACTOR_ID = "threat-actor--8e2e2d2b-17d4-4cbf-938f-98ee46b3cd3f"
 TOOL_ID = "tool--8e2e2d2b-17d4-4cbf-938f-98ee46b3cd3f"
 SIGHTING_ID = "sighting--bfbc19db-ec35-4e45-beed-f8bde2a772fb"
diff --git a/stix2/test/v21/test_bundle.py b/stix2/test/v21/test_bundle.py
index b22fa64..5627b38 100644
--- a/stix2/test/v21/test_bundle.py
+++ b/stix2/test/v21/test_bundle.py
@@ -6,12 +6,12 @@ import stix2
 
 EXPECTED_BUNDLE = """{
     "type": "bundle",
-    "id": "bundle--00000000-0000-0000-0000-000000000007",
+    "id": "bundle--00000000-0000-4000-8000-000000000007",
     "objects": [
         {
             "type": "indicator",
             "spec_version": "2.1",
-            "id": "indicator--00000000-0000-0000-0000-000000000001",
+            "id": "indicator--00000000-0000-4000-8000-000000000001",
             "created": "2017-01-01T12:34:56.000Z",
             "modified": "2017-01-01T12:34:56.000Z",
             "pattern": "[file:hashes.MD5 = 'd41d8cd98f00b204e9800998ecf8427e']",
@@ -23,7 +23,7 @@ EXPECTED_BUNDLE = """{
         {
             "type": "malware",
             "spec_version": "2.1",
-            "id": "malware--00000000-0000-0000-0000-000000000003",
+            "id": "malware--00000000-0000-4000-8000-000000000003",
             "created": "2017-01-01T12:34:56.000Z",
             "modified": "2017-01-01T12:34:56.000Z",
             "name": "Cryptolocker",
@@ -35,24 +35,24 @@ EXPECTED_BUNDLE = """{
         {
             "type": "relationship",
             "spec_version": "2.1",
-            "id": "relationship--00000000-0000-0000-0000-000000000005",
+            "id": "relationship--00000000-0000-4000-8000-000000000005",
             "created": "2017-01-01T12:34:56.000Z",
             "modified": "2017-01-01T12:34:56.000Z",
             "relationship_type": "indicates",
-            "source_ref": "indicator--01234567-89ab-cdef-0123-456789abcdef",
-            "target_ref": "malware--fedcba98-7654-3210-fedc-ba9876543210"
+            "source_ref": "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
+            "target_ref": "malware--9c4638ec-f1de-4ddb-abf4-1b760417654e"
         }
     ]
 }"""
 
 EXPECTED_BUNDLE_DICT = {
     "type": "bundle",
-    "id": "bundle--00000000-0000-0000-0000-000000000007",
+    "id": "bundle--00000000-0000-4000-8000-000000000007",
     "objects": [
         {
             "type": "indicator",
             "spec_version": "2.1",
-            "id": "indicator--00000000-0000-0000-0000-000000000001",
+            "id": "indicator--00000000-0000-4000-8000-000000000001",
             "created": "2017-01-01T12:34:56.000Z",
             "modified": "2017-01-01T12:34:56.000Z",
             "pattern": "[file:hashes.MD5 = 'd41d8cd98f00b204e9800998ecf8427e']",
@@ -64,7 +64,7 @@ EXPECTED_BUNDLE_DICT = {
         {
             "type": "malware",
             "spec_version": "2.1",
-            "id": "malware--00000000-0000-0000-0000-000000000003",
+            "id": "malware--00000000-0000-4000-8000-000000000003",
             "created": "2017-01-01T12:34:56.000Z",
             "modified": "2017-01-01T12:34:56.000Z",
             "name": "Cryptolocker",
@@ -76,12 +76,12 @@ EXPECTED_BUNDLE_DICT = {
         {
             "type": "relationship",
             "spec_version": "2.1",
-            "id": "relationship--00000000-0000-0000-0000-000000000005",
+            "id": "relationship--00000000-0000-4000-8000-000000000005",
             "created": "2017-01-01T12:34:56.000Z",
             "modified": "2017-01-01T12:34:56.000Z",
             "relationship_type": "indicates",
-            "source_ref": "indicator--01234567-89ab-cdef-0123-456789abcdef",
-            "target_ref": "malware--fedcba98-7654-3210-fedc-ba9876543210"
+            "source_ref": "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
+            "target_ref": "malware--9c4638ec-f1de-4ddb-abf4-1b760417654e"
         }
     ]
 }
diff --git a/stix2/test/v21/test_custom.py b/stix2/test/v21/test_custom.py
index c9b972e..c5d8c5f 100644
--- a/stix2/test/v21/test_custom.py
+++ b/stix2/test/v21/test_custom.py
@@ -16,7 +16,7 @@ IDENTITY_CUSTOM_PROP = stix2.v21.Identity(
 def test_identity_custom_property():
     with pytest.raises(ValueError) as excinfo:
         stix2.v21.Identity(
-            id="identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+            id="identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
             created="2015-12-21T19:59:11Z",
             modified="2015-12-21T19:59:11Z",
             name="John Smith",
@@ -27,7 +27,7 @@ def test_identity_custom_property():
 
     with pytest.raises(stix2.exceptions.ExtraPropertiesError) as excinfo:
         stix2.v21.Identity(
-            id="identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+            id="identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
             created="2015-12-21T19:59:11Z",
             modified="2015-12-21T19:59:11Z",
             name="John Smith",
@@ -40,7 +40,7 @@ def test_identity_custom_property():
     assert "Unexpected properties for Identity" in str(excinfo.value)
 
     identity = stix2.v21.Identity(
-        id="identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+        id="identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
         created="2015-12-21T19:59:11Z",
         modified="2015-12-21T19:59:11Z",
         name="John Smith",
@@ -55,7 +55,7 @@ def test_identity_custom_property():
 def test_identity_custom_property_invalid():
     with pytest.raises(stix2.exceptions.ExtraPropertiesError) as excinfo:
         stix2.v21.Identity(
-            id="identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+            id="identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
             created="2015-12-21T19:59:11Z",
             modified="2015-12-21T19:59:11Z",
             name="John Smith",
@@ -69,7 +69,7 @@ def test_identity_custom_property_invalid():
 
 def test_identity_custom_property_allowed():
     identity = stix2.v21.Identity(
-        id="identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+        id="identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
         created="2015-12-21T19:59:11Z",
         modified="2015-12-21T19:59:11Z",
         name="John Smith",
@@ -84,7 +84,7 @@ def test_identity_custom_property_allowed():
     """{
         "type": "identity",
         "spec_version": "2.1",
-        "id": "identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+        "id": "identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
         "created": "2015-12-21T19:59:11Z",
         "modified": "2015-12-21T19:59:11Z",
         "name": "John Smith",
@@ -128,7 +128,7 @@ def test_custom_property_dict_in_bundled_object():
     custom_identity = {
         'type': 'identity',
         'spec_version': '2.1',
-        'id': 'identity--311b2d2d-f010-5473-83ec-1edf84858f4c',
+        'id': 'identity--311b2d2d-f010-4473-83ec-1edf84858f4c',
         'created': '2015-12-21T19:59:11Z',
         'name': 'John Smith',
         'identity_class': 'individual',
@@ -146,7 +146,7 @@ def test_custom_properties_dict_in_bundled_object():
     custom_identity = {
         'type': 'identity',
         'spec_version': '2.1',
-        'id': 'identity--311b2d2d-f010-5473-83ec-1edf84858f4c',
+        'id': 'identity--311b2d2d-f010-4473-83ec-1edf84858f4c',
         'created': '2015-12-21T19:59:11Z',
         'name': 'John Smith',
         'identity_class': 'individual',
diff --git a/stix2/test/v21/test_datastore.py b/stix2/test/v21/test_datastore.py
index 0744438..0374ac9 100644
--- a/stix2/test/v21/test_datastore.py
+++ b/stix2/test/v21/test_datastore.py
@@ -22,13 +22,13 @@ def test_datastore_smoke():
 
 def test_datastore_get_raises():
     with pytest.raises(AttributeError) as excinfo:
-        DataStoreMixin().get("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+        DataStoreMixin().get("indicator--00000000-0000-4000-8000-000000000001")
     assert "DataStoreMixin has no data source to query" == str(excinfo.value)
 
 
 def test_datastore_all_versions_raises():
     with pytest.raises(AttributeError) as excinfo:
-        DataStoreMixin().all_versions("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+        DataStoreMixin().all_versions("indicator--00000000-0000-4000-8000-000000000001")
     assert "DataStoreMixin has no data source to query" == str(excinfo.value)
 
 
@@ -46,14 +46,14 @@ def test_datastore_creator_of_raises():
 
 def test_datastore_relationships_raises():
     with pytest.raises(AttributeError) as excinfo:
-        DataStoreMixin().relationships(obj="indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+        DataStoreMixin().relationships(obj="indicator--00000000-0000-4000-8000-000000000001",
                                        target_only=True)
     assert "DataStoreMixin has no data source to query" == str(excinfo.value)
 
 
 def test_datastore_related_to_raises():
     with pytest.raises(AttributeError) as excinfo:
-        DataStoreMixin().related_to(obj="indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+        DataStoreMixin().related_to(obj="indicator--00000000-0000-4000-8000-000000000001",
                                     target_only=True)
     assert "DataStoreMixin has no data source to query" == str(excinfo.value)
 
@@ -66,13 +66,13 @@ def test_datastore_add_raises():
 
 def test_composite_datastore_get_raises_error():
     with pytest.raises(AttributeError) as excinfo:
-        CompositeDataSource().get("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+        CompositeDataSource().get("indicator--00000000-0000-4000-8000-000000000001")
     assert "CompositeDataSource has no data sources" == str(excinfo.value)
 
 
 def test_composite_datastore_all_versions_raises_error():
     with pytest.raises(AttributeError) as excinfo:
-        CompositeDataSource().all_versions("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+        CompositeDataSource().all_versions("indicator--00000000-0000-4000-8000-000000000001")
     assert "CompositeDataSource has no data sources" == str(excinfo.value)
 
 
@@ -84,28 +84,28 @@ def test_composite_datastore_query_raises_error():
 
 def test_composite_datastore_relationships_raises_error():
     with pytest.raises(AttributeError) as excinfo:
-        CompositeDataSource().relationships(obj="indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+        CompositeDataSource().relationships(obj="indicator--00000000-0000-4000-8000-000000000001",
                                             target_only=True)
     assert "CompositeDataSource has no data sources" == str(excinfo.value)
 
 
 def test_composite_datastore_related_to_raises_error():
     with pytest.raises(AttributeError) as excinfo:
-        CompositeDataSource().related_to(obj="indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+        CompositeDataSource().related_to(obj="indicator--00000000-0000-4000-8000-000000000001",
                                          target_only=True)
     assert "CompositeDataSource has no data sources" == str(excinfo.value)
 
 
 def test_composite_datastore_add_data_source_raises_error():
     with pytest.raises(TypeError) as excinfo:
-        ind = "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f"
+        ind = "indicator--00000000-0000-4000-8000-000000000001"
         CompositeDataSource().add_data_source(ind)
     assert "DataSource (to be added) is not of type stix2.DataSource. DataSource type is '{}'".format(type(ind)) == str(excinfo.value)
 
 
 def test_composite_datastore_add_data_sources_raises_error():
     with pytest.raises(TypeError) as excinfo:
-        ind = "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f"
+        ind = "indicator--00000000-0000-4000-8000-000000000001"
         CompositeDataSource().add_data_sources(ind)
     assert "DataSource (to be added) is not of type stix2.DataSource. DataSource type is '{}'".format(type(ind)) == str(excinfo.value)
 
@@ -113,5 +113,5 @@ def test_composite_datastore_add_data_sources_raises_error():
 def test_composite_datastore_no_datasource():
     cds = CompositeDataSource()
     with pytest.raises(AttributeError) as excinfo:
-        cds.get("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+        cds.get("indicator--00000000-0000-4000-8000-000000000001")
     assert 'CompositeDataSource has no data source' in str(excinfo.value)
diff --git a/stix2/test/v21/test_datastore_composite.py b/stix2/test/v21/test_datastore_composite.py
index cdcfa21..c4f39a3 100644
--- a/stix2/test/v21/test_datastore_composite.py
+++ b/stix2/test/v21/test_datastore_composite.py
@@ -40,16 +40,16 @@ def test_composite_datasource_operations(stix_objs1, stix_objs2):
     cds1.add_data_sources([ds1_1, ds1_2])
     cds2.add_data_sources([ds2_1, ds2_2])
 
-    indicators = cds1.all_versions("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+    indicators = cds1.all_versions("indicator--00000000-0000-4000-8000-000000000001")
 
     # In STIX_OBJS2 changed the 'modified' property to a later time...
     assert len(indicators) == 2
 
     cds1.add_data_sources([cds2])
 
-    indicator = cds1.get("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+    indicator = cds1.get("indicator--00000000-0000-4000-8000-000000000001")
 
-    assert indicator["id"] == "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f"
+    assert indicator["id"] == "indicator--00000000-0000-4000-8000-000000000001"
     assert indicator["modified"] == "2017-01-31T13:49:53.935Z"
     assert indicator["type"] == "indicator"
 
@@ -69,15 +69,15 @@ def test_composite_datasource_operations(stix_objs1, stix_objs2):
     # original time in STIX_OBJS1
     assert len(results) == 3
 
-    indicator = cds1.get("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+    indicator = cds1.get("indicator--00000000-0000-4000-8000-000000000001")
 
-    assert indicator["id"] == "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f"
+    assert indicator["id"] == "indicator--00000000-0000-4000-8000-000000000001"
     assert indicator["modified"] == "2017-01-31T13:49:53.935Z"
     assert indicator["type"] == "indicator"
 
     # There is only one indicator with different ID. Since we use the same data
     # when deduplicated, only two indicators (one with different modified).
-    results = cds1.all_versions("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+    results = cds1.all_versions("indicator--00000000-0000-4000-8000-000000000001")
     assert len(results) == 2
 
     # Since we have filters already associated with our CompositeSource providing
diff --git a/stix2/test/v21/test_datastore_filesystem.py b/stix2/test/v21/test_datastore_filesystem.py
index 7666611..408c23a 100644
--- a/stix2/test/v21/test_datastore_filesystem.py
+++ b/stix2/test/v21/test_datastore_filesystem.py
@@ -198,7 +198,7 @@ def test_filesystem_sink_add_stix_object_dict(fs_sink, fs_source):
         "type": "campaign",
         "objective": "German and French Intelligence Services",
         "aliases": ["Purple Robes"],
-        "id": "campaign--111111b6-1112-4fb0-111b-b111107ca70a",
+        "id": "campaign--8e2e2d2b-17d4-4cbf-938f-98ee46b3cd3f",
         "created": "2017-05-31T21:31:53.197755Z"
     }
 
@@ -218,14 +218,14 @@ def test_filesystem_sink_add_stix_bundle_dict(fs_sink, fs_source):
     # add stix bundle dict
     bund = {
         "type": "bundle",
-        "id": "bundle--112211b6-1112-4fb0-111b-b111107ca70a",
+        "id": "bundle--040ae5ec-2e91-4e94-b075-bc8b368e8ca3",
         "objects": [
             {
                 "name": "Atilla",
                 "type": "campaign",
                 "objective": "Bulgarian, Albanian and Romanian Intelligence Services",
                 "aliases": ["Huns"],
-                "id": "campaign--133111b6-1112-4fb0-111b-b111107ca70a",
+                "id": "campaign--b8f86161-ccae-49de-973a-4ca320c62478",
                 "created": "2017-05-31T21:31:53.197755Z"
             }
         ]
@@ -245,15 +245,15 @@ def test_filesystem_sink_add_stix_bundle_dict(fs_sink, fs_source):
 
 def test_filesystem_sink_add_json_stix_object(fs_sink, fs_source):
     # add json-encoded stix obj
-    camp4 = '{"type": "campaign", "id":"campaign--144111b6-1112-4fb0-111b-b111107ca70a",'\
+    camp4 = '{"type": "campaign", "id":"campaign--6a6ca372-ba07-42cc-81ef-9840fc1f963d",'\
             ' "created":"2017-05-31T21:31:53.197755Z", "name": "Ghengis Khan", "objective": "China and Russian infrastructure"}'
 
     fs_sink.add(camp4)
 
-    assert os.path.exists(os.path.join(FS_PATH, "campaign", "campaign--144111b6-1112-4fb0-111b-b111107ca70a" + ".json"))
+    assert os.path.exists(os.path.join(FS_PATH, "campaign", "campaign--6a6ca372-ba07-42cc-81ef-9840fc1f963d" + ".json"))
 
-    camp4_r = fs_source.get("campaign--144111b6-1112-4fb0-111b-b111107ca70a")
-    assert camp4_r.id == "campaign--144111b6-1112-4fb0-111b-b111107ca70a"
+    camp4_r = fs_source.get("campaign--6a6ca372-ba07-42cc-81ef-9840fc1f963d")
+    assert camp4_r.id == "campaign--6a6ca372-ba07-42cc-81ef-9840fc1f963d"
     assert camp4_r.name == "Ghengis Khan"
 
     os.remove(os.path.join(FS_PATH, "campaign", camp4_r.id + ".json"))
@@ -261,15 +261,15 @@ def test_filesystem_sink_add_json_stix_object(fs_sink, fs_source):
 
 def test_filesystem_sink_json_stix_bundle(fs_sink, fs_source):
     # add json-encoded stix bundle
-    bund2 = '{"type": "bundle", "id": "bundle--332211b6-1132-4fb0-111b-b111107ca70a",' \
-            ' "objects": [{"type": "campaign", "spec_version": "2.1", "id": "campaign--155155b6-1112-4fb0-111b-b111107ca70a",' \
+    bund2 = '{"type": "bundle", "id": "bundle--3d267103-8475-4d8f-b321-35ec6eccfa37",' \
+            ' "objects": [{"type": "campaign", "spec_version": "2.1", "id": "campaign--2c03b8bf-82ee-433e-9918-ca2cb6e9534b",' \
             ' "created":"2017-05-31T21:31:53.197755Z", "name": "Spartacus", "objective": "Oppressive regimes of Africa and Middle East"}]}'
     fs_sink.add(bund2)
 
-    assert os.path.exists(os.path.join(FS_PATH, "campaign", "campaign--155155b6-1112-4fb0-111b-b111107ca70a" + ".json"))
+    assert os.path.exists(os.path.join(FS_PATH, "campaign", "campaign--2c03b8bf-82ee-433e-9918-ca2cb6e9534b" + ".json"))
 
-    camp5_r = fs_source.get("campaign--155155b6-1112-4fb0-111b-b111107ca70a")
-    assert camp5_r.id == "campaign--155155b6-1112-4fb0-111b-b111107ca70a"
+    camp5_r = fs_source.get("campaign--2c03b8bf-82ee-433e-9918-ca2cb6e9534b")
+    assert camp5_r.id == "campaign--2c03b8bf-82ee-433e-9918-ca2cb6e9534b"
     assert camp5_r.name == "Spartacus"
 
     os.remove(os.path.join(FS_PATH, "campaign", camp5_r.id + ".json"))
@@ -287,14 +287,14 @@ def test_filesystem_sink_add_objects_list(fs_sink, fs_source):
         "spec_version": "2.1",
         "objective": "Central and Eastern Europe military commands and departments",
         "aliases": ["The Frenchmen"],
-        "id": "campaign--122818b6-1112-4fb0-111b-b111107ca70a",
+        "id": "campaign--122818b6-1112-4fb0-b11b-b111107ca70a",
         "created": "2017-05-31T21:31:53.197755Z"
     }
 
     fs_sink.add([camp6, camp7])
 
     assert os.path.exists(os.path.join(FS_PATH, "campaign", camp6.id + ".json"))
-    assert os.path.exists(os.path.join(FS_PATH, "campaign", "campaign--122818b6-1112-4fb0-111b-b111107ca70a" + ".json"))
+    assert os.path.exists(os.path.join(FS_PATH, "campaign", "campaign--122818b6-1112-4fb0-b11b-b111107ca70a" + ".json"))
 
     camp6_r = fs_source.get(camp6.id)
     assert camp6_r.id == camp6.id
@@ -402,7 +402,7 @@ def test_filesystem_add_bundle_object(fs_store):
 
 
 def test_filesystem_store_add_invalid_object(fs_store):
-    ind = ('campaign', 'campaign--111111b6-1112-4fb0-111b-b111107ca70a')  # tuple isn't valid
+    ind = ('campaign', 'campaign--8e2e2d2b-17d4-4cbf-938f-98ee46b3cd3f')   # tuple isn't valid
     with pytest.raises(TypeError) as excinfo:
         fs_store.add(ind)
     assert 'stix_data must be' in str(excinfo.value)
diff --git a/stix2/test/v21/test_datastore_filters.py b/stix2/test/v21/test_datastore_filters.py
index a51a4d7..1e13bec 100644
--- a/stix2/test/v21/test_datastore_filters.py
+++ b/stix2/test/v21/test_datastore_filters.py
@@ -8,7 +8,7 @@ stix_objs = [
     {
         "created": "2017-01-27T13:49:53.997Z",
         "description": "\n\nTITLE:\n\tPoison Ivy",
-        "id": "malware--fdd60b30-b67c-11e3-b0b9-f01faf20d111",
+        "id": "malware--fdd60b30-b67c-41e3-b0b9-f01faf20d111",
         "spec_version": "2.1",
         "labels": [
             "remote-access-trojan"
@@ -20,7 +20,7 @@ stix_objs = [
     },
     {
         "created": "2014-05-08T09:00:00.000Z",
-        "id": "indicator--a932fcc6-e032-176c-126f-cb970a5a1ade",
+        "id": "indicator--a932fcc6-e032-476c-826f-cb970a5a1ade",
         "labels": [
             "file-hash-watchlist"
         ],
@@ -48,16 +48,16 @@ stix_objs = [
         ],
         "relationship_type": "indicates",
         "revoked": True,
-        "source_ref": "indicator--a932fcc6-e032-176c-126f-cb970a5a1ade",
+        "source_ref": "indicator--a932fcc6-e032-476c-826f-cb970a5a1ade",
         "spec_version": "2.1",
-        "target_ref": "malware--fdd60b30-b67c-11e3-b0b9-f01faf20d111",
+        "target_ref": "malware--fdd60b30-b67c-41e3-b0b9-f01faf20d111",
         "type": "relationship"
     },
     {
         "id": "vulnerability--ee916c28-c7a4-4d0d-ad56-a8d357f89fef",
         "spec_version": "2.1",
         "created": "2016-02-14T00:00:00.000Z",
-        "created_by_ref": "identity--00000000-0000-0000-0000-b8e91df99dc9",
+        "created_by_ref": "identity--f1350682-3290-4e0d-be58-69e290537647",
         "modified": "2016-02-14T00:00:00.000Z",
         "type": "vulnerability",
         "name": "CVE-2014-0160",
@@ -102,11 +102,13 @@ filters = [
     Filter("granular_markings.selectors", "in", "relationship_type"),
     Filter("granular_markings.marking_ref", "=", "marking-definition--5e57c739-391a-4eb3-b6be-7d15ca92d5ed"),
     Filter("external_references.external_id", "in", "CVE-2014-0160,CVE-2017-6608"),
-    Filter("created_by_ref", "=", "identity--00000000-0000-0000-0000-b8e91df99dc9"),
-    Filter("object_marking_refs", "=", "marking-definition--613f2e26-0000-0000-0000-b8e91df99dc9"),
+    Filter("created_by_ref", "=", "identity--f1350682-3290-4e0d-be58-69e290537647"),
+    Filter("object_marking_refs", "=", "marking-definition--613f2e26-0000-4000-8000-b8e91df99dc9"),
     Filter("granular_markings.selectors", "in", "description"),
     Filter("external_references.source_name", "=", "CVE"),
-    Filter("objects", "=", {"0": {"type": "file", "name": "HAL 9000.exe"}})
+    Filter("objects", "=", {"0": {"type": "file", "name": "HAL 9000.exe"}}),
+    Filter("objects", "contains", {"type": "file", "name": "HAL 9000.exe"}),
+    Filter("labels", "contains", "heartbleed"),
 ]
 
 # same as above objects but converted to real Python STIX2 objects
@@ -268,7 +270,7 @@ def test_apply_common_filters9():
 
 
 def test_apply_common_filters10():
-    # "Return any object that matches marking-definition--613f2e26-0000-0000-0000-b8e91df99dc9 in object_marking_refs" (None)
+    # "Return any object that matches marking-definition--613f2e26-0000-4000-8000-b8e91df99dc9 in object_marking_refs" (None)
     resp = list(apply_common_filters(stix_objs, [filters[11]]))
     assert len(resp) == 0
 
@@ -308,6 +310,28 @@ def test_apply_common_filters13():
     assert len(resp) == 1
 
 
+def test_apply_common_filters14():
+    # Return any object that contains a specific File Cyber Observable Object
+    resp = list(apply_common_filters(stix_objs, [filters[15]]))
+    assert resp[0]['id'] == stix_objs[4]['id']
+    assert len(resp) == 1
+
+    resp = list(apply_common_filters(real_stix_objs, [filters[15]]))
+    assert resp[0].id == real_stix_objs[4].id
+    assert len(resp) == 1
+
+
+def test_apply_common_filters15():
+    # Return any object that contains 'heartbleed' in "labels"
+    resp = list(apply_common_filters(stix_objs, [filters[16]]))
+    assert resp[0]['id'] == stix_objs[3]['id']
+    assert len(resp) == 1
+
+    resp = list(apply_common_filters(real_stix_objs, [filters[16]]))
+    assert resp[0].id == real_stix_objs[3].id
+    assert len(resp) == 1
+
+
 def test_datetime_filter_behavior():
     """if a filter is initialized with its value being a datetime object
     OR the STIX object property being filtered on is a datetime object, all
@@ -401,12 +425,12 @@ def test_filters4():
 
 
 def test_filters5(stix_objs2, real_stix_objs2):
-    # "Return any object whose id is not indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f"
-    resp = list(apply_common_filters(stix_objs2, [Filter("id", "!=", "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f")]))
+    # "Return any object whose id is not indicator--00000000-0000-4000-8000-000000000002"
+    resp = list(apply_common_filters(stix_objs2, [Filter("id", "!=", "indicator--00000000-0000-4000-8000-000000000002")]))
     assert resp[0]['id'] == stix_objs2[0]['id']
     assert len(resp) == 1
 
-    resp = list(apply_common_filters(real_stix_objs2, [Filter("id", "!=", "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f")]))
+    resp = list(apply_common_filters(real_stix_objs2, [Filter("id", "!=", "indicator--00000000-0000-4000-8000-000000000002")]))
     assert resp[0].id == real_stix_objs2[0].id
     assert len(resp) == 1
 
diff --git a/stix2/test/v21/test_datastore_memory.py b/stix2/test/v21/test_datastore_memory.py
index 74dac2e..c8fce0f 100644
--- a/stix2/test/v21/test_datastore_memory.py
+++ b/stix2/test/v21/test_datastore_memory.py
@@ -14,7 +14,7 @@ from .constants import (CAMPAIGN_ID, CAMPAIGN_KWARGS, IDENTITY_ID,
 
 IND1 = {
     "created": "2017-01-27T13:49:53.935Z",
-    "id": "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+    "id": "indicator--00000000-0000-4000-8000-000000000001",
     "labels": [
         "url-watchlist"
     ],
@@ -27,7 +27,7 @@ IND1 = {
 }
 IND2 = {
     "created": "2017-01-27T13:49:53.935Z",
-    "id": "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+    "id": "indicator--00000000-0000-4000-8000-000000000001",
     "labels": [
         "url-watchlist"
     ],
@@ -40,7 +40,7 @@ IND2 = {
 }
 IND3 = {
     "created": "2017-01-27T13:49:53.935Z",
-    "id": "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+    "id": "indicator--00000000-0000-4000-8000-000000000001",
     "labels": [
         "url-watchlist"
     ],
@@ -53,7 +53,7 @@ IND3 = {
 }
 IND4 = {
     "created": "2017-01-27T13:49:53.935Z",
-    "id": "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f",
+    "id": "indicator--00000000-0000-4000-8000-000000000002",
     "labels": [
         "url-watchlist"
     ],
@@ -66,7 +66,7 @@ IND4 = {
 }
 IND5 = {
     "created": "2017-01-27T13:49:53.935Z",
-    "id": "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f",
+    "id": "indicator--00000000-0000-4000-8000-000000000002",
     "labels": [
         "url-watchlist"
     ],
@@ -79,7 +79,7 @@ IND5 = {
 }
 IND6 = {
     "created": "2017-01-27T13:49:53.935Z",
-    "id": "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",
+    "id": "indicator--00000000-0000-4000-8000-000000000001",
     "labels": [
         "url-watchlist"
     ],
@@ -92,7 +92,7 @@ IND6 = {
 }
 IND7 = {
     "created": "2017-01-27T13:49:53.935Z",
-    "id": "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f",
+    "id": "indicator--00000000-0000-4000-8000-000000000002",
     "labels": [
         "url-watchlist"
     ],
@@ -105,7 +105,7 @@ IND7 = {
 }
 IND8 = {
     "created": "2017-01-27T13:49:53.935Z",
-    "id": "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f",
+    "id": "indicator--00000000-0000-4000-8000-000000000002",
     "labels": [
         "url-watchlist"
     ],
@@ -158,12 +158,12 @@ def fs_mem_store(request, mem_store):
 
 
 def test_memory_source_get(mem_source):
-    resp = mem_source.get("indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f")
-    assert resp["id"] == "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f"
+    resp = mem_source.get("indicator--00000000-0000-4000-8000-000000000001")
+    assert resp["id"] == "indicator--00000000-0000-4000-8000-000000000001"
 
 
 def test_memory_source_get_nonexistant_object(mem_source):
-    resp = mem_source.get("tool--d81f86b8-975b-bc0b-775e-810c5ad45a4f")
+    resp = mem_source.get("tool--8d0b222c-7a3b-44a0-b9c6-31b051efb32e")
     assert resp is None
 
 
@@ -174,7 +174,7 @@ def test_memory_store_all_versions(mem_store):
                   spec_version="2.0",
                   type="bundle"))
 
-    resp = mem_store.all_versions("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+    resp = mem_store.all_versions("indicator--00000000-0000-4000-8000-000000000001")
     assert len(resp) == 1  # MemoryStore can only store 1 version of each object
 
 
@@ -185,7 +185,7 @@ def test_memory_store_query(mem_store):
 
 
 def test_memory_store_query_single_filter(mem_store):
-    query = Filter('id', '=', 'indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f')
+    query = Filter('id', '=', 'indicator--00000000-0000-4000-8000-000000000001')
     resp = mem_store.query(query)
     assert len(resp) == 1
 
@@ -195,15 +195,15 @@ def test_memory_store_query_empty_query(mem_store):
     # sort since returned in random order
     resp = sorted(resp, key=lambda k: k['id'])
     assert len(resp) == 2
-    assert resp[0]['id'] == 'indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f'
-    assert resp[0]['modified'] == '2017-01-27T13:49:53.935Z'
-    assert resp[1]['id'] == 'indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f'
-    assert resp[1]['modified'] == '2017-01-27T13:49:53.936Z'
+    assert resp[0]['id'] == 'indicator--00000000-0000-4000-8000-000000000001'
+    assert resp[0]['modified'] == '2017-01-27T13:49:53.936Z'
+    assert resp[1]['id'] == 'indicator--00000000-0000-4000-8000-000000000002'
+    assert resp[1]['modified'] == '2017-01-27T13:49:53.935Z'
 
 
 def test_memory_store_query_multiple_filters(mem_store):
     mem_store.source.filters.add(Filter('type', '=', 'indicator'))
-    query = Filter('id', '=', 'indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f')
+    query = Filter('id', '=', 'indicator--00000000-0000-4000-8000-000000000001')
     resp = mem_store.query(query)
     assert len(resp) == 1
 
@@ -215,13 +215,13 @@ def test_memory_store_save_load_file(mem_store, fs_mem_store):
     # (this is done in fixture 'fs_mem_store'), so can already read-in here
     contents = open(os.path.abspath(filename)).read()
 
-    assert '"id": "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f",' in contents
-    assert '"id": "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f",' in contents
+    assert '"id": "indicator--00000000-0000-4000-8000-000000000001",' in contents
+    assert '"id": "indicator--00000000-0000-4000-8000-000000000001",' in contents
 
     mem_store2 = MemoryStore()
     mem_store2.load_from_file(filename)
-    assert mem_store2.get("indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f")
-    assert mem_store2.get("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+    assert mem_store2.get("indicator--00000000-0000-4000-8000-000000000001")
+    assert mem_store2.get("indicator--00000000-0000-4000-8000-000000000001")
 
 
 def test_memory_store_add_invalid_object(mem_store):
diff --git a/stix2/test/v21/test_datastore_taxii.py b/stix2/test/v21/test_datastore_taxii.py
index cc78c2a..96040e0 100644
--- a/stix2/test/v21/test_datastore_taxii.py
+++ b/stix2/test/v21/test_datastore_taxii.py
@@ -253,7 +253,7 @@ def test_add_dict_bundle_object(collection):
 def test_get_stix2_object(collection):
     tc_sink = stix2.TAXIICollectionSource(collection)
 
-    objects = tc_sink.get("indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f")
+    objects = tc_sink.get("indicator--00000000-0000-4000-8000-000000000001")
 
     assert objects
 
@@ -320,7 +320,7 @@ def test_add_get_remove_filter(collection):
 def test_get_all_versions(collection):
     ds = stix2.TAXIICollectionStore(collection)
 
-    indicators = ds.all_versions('indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f')
+    indicators = ds.all_versions('indicator--00000000-0000-4000-8000-000000000001')
     # There are 3 indicators but 2 share the same 'modified' timestamp
     assert len(indicators) == 2
 
diff --git a/stix2/test/v21/test_environment.py b/stix2/test/v21/test_environment.py
index f455f6a..7f839e3 100644
--- a/stix2/test/v21/test_environment.py
+++ b/stix2/test/v21/test_environment.py
@@ -191,7 +191,7 @@ def test_parse_malware():
     data = """{
         "type": "malware",
         "spec_version": "2.1",
-        "id": "malware--fedcba98-7654-3210-fedc-ba9876543210",
+        "id": "malware--9c4638ec-f1de-4ddb-abf4-1b760417654e",
         "created": "2017-01-01T12:34:56.000Z",
         "modified": "2017-01-01T12:34:56.000Z",
         "name": "Cryptolocker",
diff --git a/stix2/test/v21/test_fixtures.py b/stix2/test/v21/test_fixtures.py
index 83d5f85..23ad8a4 100644
--- a/stix2/test/v21/test_fixtures.py
+++ b/stix2/test/v21/test_fixtures.py
@@ -10,9 +10,9 @@ def test_clock(clock):
 
 
 def test_my_uuid4_fixture(uuid4):
-    assert uuid.uuid4() == "00000000-0000-0000-0000-000000000001"
-    assert uuid.uuid4() == "00000000-0000-0000-0000-000000000002"
-    assert uuid.uuid4() == "00000000-0000-0000-0000-000000000003"
+    assert uuid.uuid4() == "00000000-0000-4000-8000-000000000001"
+    assert uuid.uuid4() == "00000000-0000-4000-8000-000000000002"
+    assert uuid.uuid4() == "00000000-0000-4000-8000-000000000003"
     for _ in range(256):
         uuid.uuid4()
-    assert uuid.uuid4() == "00000000-0000-0000-0000-000000000104"
+    assert uuid.uuid4() == "00000000-0000-4000-8000-000000000104"
diff --git a/stix2/test/v21/test_identity.py b/stix2/test/v21/test_identity.py
index 13225e4..0a3399b 100644
--- a/stix2/test/v21/test_identity.py
+++ b/stix2/test/v21/test_identity.py
@@ -10,7 +10,7 @@ from .constants import IDENTITY_ID
 EXPECTED = """{
     "type": "identity",
     "spec_version": "2.1",
-    "id": "identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+    "id": "identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
     "created": "2015-12-21T19:59:11.000Z",
     "modified": "2015-12-21T19:59:11.000Z",
     "name": "John Smith",
@@ -20,7 +20,7 @@ EXPECTED = """{
 
 def test_identity_example():
     identity = stix2.v21.Identity(
-        id="identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+        id="identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
         created="2015-12-21T19:59:11.000Z",
         modified="2015-12-21T19:59:11.000Z",
         name="John Smith",
@@ -34,7 +34,7 @@ def test_identity_example():
     EXPECTED,
     {
         "created": "2015-12-21T19:59:11.000Z",
-        "id": "identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+        "id": "identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
         "identity_class": "individual",
         "modified": "2015-12-21T19:59:11.000Z",
         "name": "John Smith",
@@ -57,7 +57,7 @@ def test_parse_no_type():
     with pytest.raises(stix2.exceptions.ParseError):
         stix2.parse("""
         {
-            "id": "identity--311b2d2d-f010-5473-83ec-1edf84858f4c",
+            "id": "identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
             "created": "2015-12-21T19:59:11.000Z",
             "modified": "2015-12-21T19:59:11.000Z",
             "name": "John Smith",
diff --git a/stix2/test/v21/test_indicator.py b/stix2/test/v21/test_indicator.py
index 71685cd..de777ee 100644
--- a/stix2/test/v21/test_indicator.py
+++ b/stix2/test/v21/test_indicator.py
@@ -11,7 +11,7 @@ from .constants import FAKE_TIME, INDICATOR_ID, INDICATOR_KWARGS
 EXPECTED_INDICATOR = """{
     "type": "indicator",
     "spec_version": "2.1",
-    "id": "indicator--01234567-89ab-cdef-0123-456789abcdef",
+    "id": "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
     "created": "2017-01-01T00:00:01.000Z",
     "modified": "2017-01-01T00:00:01.000Z",
     "pattern": "[file:hashes.MD5 = 'd41d8cd98f00b204e9800998ecf8427e']",
@@ -24,7 +24,7 @@ EXPECTED_INDICATOR = """{
 EXPECTED_INDICATOR_REPR = "Indicator(" + " ".join("""
     type='indicator',
     spec_version='2.1',
-    id='indicator--01234567-89ab-cdef-0123-456789abcdef',
+    id='indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7',
     created='2017-01-01T00:00:01.000Z',
     modified='2017-01-01T00:00:01.000Z',
     pattern="[file:hashes.MD5 = 'd41d8cd98f00b204e9800998ecf8427e']",
@@ -56,7 +56,7 @@ def test_indicator_with_all_required_properties():
 def test_indicator_autogenerated_properties(indicator):
     assert indicator.type == 'indicator'
     assert indicator.spec_version == '2.1'
-    assert indicator.id == 'indicator--00000000-0000-0000-0000-000000000001'
+    assert indicator.id == 'indicator--00000000-0000-4000-8000-000000000001'
     assert indicator.created == FAKE_TIME
     assert indicator.modified == FAKE_TIME
     assert indicator.labels == ['malicious-activity']
@@ -65,7 +65,7 @@ def test_indicator_autogenerated_properties(indicator):
 
     assert indicator['type'] == 'indicator'
     assert indicator['spec_version'] == '2.1'
-    assert indicator['id'] == 'indicator--00000000-0000-0000-0000-000000000001'
+    assert indicator['id'] == 'indicator--00000000-0000-4000-8000-000000000001'
     assert indicator['created'] == FAKE_TIME
     assert indicator['modified'] == FAKE_TIME
     assert indicator['labels'] == ['malicious-activity']
@@ -156,7 +156,7 @@ def test_created_modified_time_are_identical_by_default():
     EXPECTED_INDICATOR,
     {
         "type": "indicator",
-        "id": "indicator--01234567-89ab-cdef-0123-456789abcdef",
+        "id": "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
         "created": "2017-01-01T00:00:01Z",
         "modified": "2017-01-01T00:00:01Z",
         "labels": [
diff --git a/stix2/test/v21/test_malware.py b/stix2/test/v21/test_malware.py
index 01e0da9..c218bbb 100644
--- a/stix2/test/v21/test_malware.py
+++ b/stix2/test/v21/test_malware.py
@@ -11,7 +11,7 @@ from .constants import FAKE_TIME, MALWARE_ID, MALWARE_KWARGS
 EXPECTED_MALWARE = """{
     "type": "malware",
     "spec_version": "2.1",
-    "id": "malware--fedcba98-7654-3210-fedc-ba9876543210",
+    "id": "malware--9c4638ec-f1de-4ddb-abf4-1b760417654e",
     "created": "2016-05-12T08:17:27.000Z",
     "modified": "2016-05-12T08:17:27.000Z",
     "name": "Cryptolocker",
@@ -40,14 +40,14 @@ def test_malware_with_all_required_properties():
 
 def test_malware_autogenerated_properties(malware):
     assert malware.type == 'malware'
-    assert malware.id == 'malware--00000000-0000-0000-0000-000000000001'
+    assert malware.id == 'malware--00000000-0000-4000-8000-000000000001'
     assert malware.created == FAKE_TIME
     assert malware.modified == FAKE_TIME
     assert malware.labels == ['ransomware']
     assert malware.name == "Cryptolocker"
 
     assert malware['type'] == 'malware'
-    assert malware['id'] == 'malware--00000000-0000-0000-0000-000000000001'
+    assert malware['id'] == 'malware--00000000-0000-4000-8000-000000000001'
     assert malware['created'] == FAKE_TIME
     assert malware['modified'] == FAKE_TIME
     assert malware['labels'] == ['ransomware']
@@ -111,7 +111,7 @@ def test_invalid_kwarg_to_malware():
     {
         "type": "malware",
         "spec_version": "2.1",
-        "id": "malware--fedcba98-7654-3210-fedc-ba9876543210",
+        "id": "malware--9c4638ec-f1de-4ddb-abf4-1b760417654e",
         "created": "2016-05-12T08:17:27.000Z",
         "modified": "2016-05-12T08:17:27.000Z",
         "labels": ["ransomware"],
diff --git a/stix2/test/v21/test_properties.py b/stix2/test/v21/test_properties.py
index 3653540..3ad7126 100644
--- a/stix2/test/v21/test_properties.py
+++ b/stix2/test/v21/test_properties.py
@@ -1,16 +1,19 @@
+import uuid
+
 import pytest
 
 import stix2
 from stix2.exceptions import AtLeastOnePropertyError, DictionaryKeyError
-from stix2.properties import (BinaryProperty, BooleanProperty,
-                              DictionaryProperty, EmbeddedObjectProperty,
-                              EnumProperty, ExtensionsProperty, FloatProperty,
+from stix2.properties import (ERROR_INVALID_ID, BinaryProperty,
+                              BooleanProperty, DictionaryProperty,
+                              EmbeddedObjectProperty, EnumProperty,
+                              ExtensionsProperty, FloatProperty,
                               HashesProperty, HexProperty, IDProperty,
                               IntegerProperty, ListProperty, Property,
                               ReferenceProperty, StringProperty,
                               TimestampProperty, TypeProperty)
 
-from .constants import FAKE_TIME
+from . import constants
 
 
 def test_property():
@@ -86,18 +89,68 @@ def test_type_property():
     assert prop.clean(prop.default())
 
 
-def test_id_property():
-    idprop = IDProperty('my-type')
+ID_PROP = IDProperty('my-type')
+MY_ID = 'my-type--232c9d3f-49fc-4440-bb01-607f638778e7'
 
-    assert idprop.clean('my-type--90aaca8a-1110-5d32-956d-ac2f34a1bd8c')
+
+@pytest.mark.parametrize("value", [
+    MY_ID,
+    'my-type--00000000-0000-4000-8000-000000000000',
+])
+def test_id_property_valid(value):
+    assert ID_PROP.clean(value) == value
+
+
+CONSTANT_IDS = [
+    constants.ATTACK_PATTERN_ID,
+    constants.CAMPAIGN_ID,
+    constants.COURSE_OF_ACTION_ID,
+    constants.IDENTITY_ID,
+    constants.INDICATOR_ID,
+    constants.INTRUSION_SET_ID,
+    constants.MALWARE_ID,
+    constants.MARKING_DEFINITION_ID,
+    constants.OBSERVED_DATA_ID,
+    constants.RELATIONSHIP_ID,
+    constants.REPORT_ID,
+    constants.SIGHTING_ID,
+    constants.THREAT_ACTOR_ID,
+    constants.TOOL_ID,
+    constants.VULNERABILITY_ID,
+]
+CONSTANT_IDS.extend(constants.MARKING_IDS)
+CONSTANT_IDS.extend(constants.RELATIONSHIP_IDS)
+
+
+@pytest.mark.parametrize("value", CONSTANT_IDS)
+def test_id_property_valid_for_type(value):
+    type = value.split('--', 1)[0]
+    assert IDProperty(type=type).clean(value) == value
+
+
+def test_id_property_wrong_type():
     with pytest.raises(ValueError) as excinfo:
-        idprop.clean('not-my-type--90aaca8a-1110-5d32-956d-ac2f34a1bd8c')
+        ID_PROP.clean('not-my-type--232c9d3f-49fc-4440-bb01-607f638778e7')
     assert str(excinfo.value) == "must start with 'my-type--'."
-    with pytest.raises(ValueError) as excinfo:
-        idprop.clean('my-type--foo')
-    assert str(excinfo.value) == "must have a valid UUID after the prefix."
 
-    assert idprop.clean(idprop.default())
+
+@pytest.mark.parametrize("value", [
+    'my-type--foo',
+    # Not a v4 UUID
+    'my-type--00000000-0000-0000-0000-000000000000',
+    'my-type--' + str(uuid.uuid1()),
+    'my-type--' + str(uuid.uuid3(uuid.NAMESPACE_DNS, "example.org")),
+    'my-type--' + str(uuid.uuid5(uuid.NAMESPACE_DNS, "example.org")),
+])
+def test_id_property_not_a_valid_hex_uuid(value):
+    with pytest.raises(ValueError) as excinfo:
+        ID_PROP.clean(value)
+    assert str(excinfo.value) == ERROR_INVALID_ID
+
+
+def test_id_property_default():
+    default = ID_PROP.default()
+    assert ID_PROP.clean(default) == default
 
 
 @pytest.mark.parametrize("value", [
@@ -180,10 +233,14 @@ def test_boolean_property_invalid(value):
 def test_reference_property():
     ref_prop = ReferenceProperty()
 
-    assert ref_prop.clean("my-type--3a331bfe-0566-55e1-a4a0-9a2cd355a300")
+    assert ref_prop.clean("my-type--00000000-0000-4000-8000-000000000000")
     with pytest.raises(ValueError):
         ref_prop.clean("foo")
 
+    # This is not a valid V4 UUID
+    with pytest.raises(ValueError):
+        ref_prop.clean("my-type--00000000-0000-0000-0000-000000000000")
+
 
 @pytest.mark.parametrize("value", [
     '2017-01-01T12:34:56Z',
@@ -192,7 +249,7 @@ def test_reference_property():
 ])
 def test_timestamp_property_valid(value):
     ts_prop = TimestampProperty()
-    assert ts_prop.clean(value) == FAKE_TIME
+    assert ts_prop.clean(value) == constants.FAKE_TIME
 
 
 def test_timestamp_property_invalid():
diff --git a/stix2/test/v21/test_relationship.py b/stix2/test/v21/test_relationship.py
index 51e03ff..fe76f17 100644
--- a/stix2/test/v21/test_relationship.py
+++ b/stix2/test/v21/test_relationship.py
@@ -11,12 +11,12 @@ from .constants import (FAKE_TIME, INDICATOR_ID, MALWARE_ID, RELATIONSHIP_ID,
 EXPECTED_RELATIONSHIP = """{
     "type": "relationship",
     "spec_version": "2.1",
-    "id": "relationship--00000000-1111-2222-3333-444444444444",
+    "id": "relationship--df7c87eb-75d2-4948-af81-9d49d246f301",
     "created": "2016-04-06T20:06:37.000Z",
     "modified": "2016-04-06T20:06:37.000Z",
     "relationship_type": "indicates",
-    "source_ref": "indicator--01234567-89ab-cdef-0123-456789abcdef",
-    "target_ref": "malware--fedcba98-7654-3210-fedc-ba9876543210"
+    "source_ref": "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
+    "target_ref": "malware--9c4638ec-f1de-4ddb-abf4-1b760417654e"
 }"""
 
 
@@ -38,7 +38,7 @@ def test_relationship_all_required_properties():
 def test_relationship_autogenerated_properties(relationship):
     assert relationship.type == 'relationship'
     assert relationship.spec_version == '2.1'
-    assert relationship.id == 'relationship--00000000-0000-0000-0000-000000000001'
+    assert relationship.id == 'relationship--00000000-0000-4000-8000-000000000001'
     assert relationship.created == FAKE_TIME
     assert relationship.modified == FAKE_TIME
     assert relationship.relationship_type == 'indicates'
@@ -47,7 +47,7 @@ def test_relationship_autogenerated_properties(relationship):
 
     assert relationship['type'] == 'relationship'
     assert relationship['spec_version'] == '2.1'
-    assert relationship['id'] == 'relationship--00000000-0000-0000-0000-000000000001'
+    assert relationship['id'] == 'relationship--00000000-0000-4000-8000-000000000001'
     assert relationship['created'] == FAKE_TIME
     assert relationship['modified'] == FAKE_TIME
     assert relationship['relationship_type'] == 'indicates'
@@ -125,29 +125,29 @@ def test_create_relationship_from_objects_rather_than_ids(indicator, malware):
     )
 
     assert rel.relationship_type == 'indicates'
-    assert rel.source_ref == 'indicator--00000000-0000-0000-0000-000000000001'
-    assert rel.target_ref == 'malware--00000000-0000-0000-0000-000000000003'
-    assert rel.id == 'relationship--00000000-0000-0000-0000-000000000005'
+    assert rel.source_ref == 'indicator--00000000-0000-4000-8000-000000000001'
+    assert rel.target_ref == 'malware--00000000-0000-4000-8000-000000000003'
+    assert rel.id == 'relationship--00000000-0000-4000-8000-000000000005'
 
 
 def test_create_relationship_with_positional_args(indicator, malware):
     rel = stix2.v21.Relationship(indicator, 'indicates', malware)
 
     assert rel.relationship_type == 'indicates'
-    assert rel.source_ref == 'indicator--00000000-0000-0000-0000-000000000001'
-    assert rel.target_ref == 'malware--00000000-0000-0000-0000-000000000003'
-    assert rel.id == 'relationship--00000000-0000-0000-0000-000000000005'
+    assert rel.source_ref == 'indicator--00000000-0000-4000-8000-000000000001'
+    assert rel.target_ref == 'malware--00000000-0000-4000-8000-000000000003'
+    assert rel.id == 'relationship--00000000-0000-4000-8000-000000000005'
 
 
 @pytest.mark.parametrize("data", [
     EXPECTED_RELATIONSHIP,
     {
         "created": "2016-04-06T20:06:37Z",
-        "id": "relationship--00000000-1111-2222-3333-444444444444",
+        "id": "relationship--df7c87eb-75d2-4948-af81-9d49d246f301",
         "modified": "2016-04-06T20:06:37Z",
         "relationship_type": "indicates",
-        "source_ref": "indicator--01234567-89ab-cdef-0123-456789abcdef",
-        "target_ref": "malware--fedcba98-7654-3210-fedc-ba9876543210",
+        "source_ref": "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
+        "target_ref": "malware--9c4638ec-f1de-4ddb-abf4-1b760417654e",
         "spec_version": "2.1",
         "type": "relationship"
     },
@@ -161,5 +161,5 @@ def test_parse_relationship(data):
     assert rel.created == dt.datetime(2016, 4, 6, 20, 6, 37, tzinfo=pytz.utc)
     assert rel.modified == dt.datetime(2016, 4, 6, 20, 6, 37, tzinfo=pytz.utc)
     assert rel.relationship_type == "indicates"
-    assert rel.source_ref == "indicator--01234567-89ab-cdef-0123-456789abcdef"
-    assert rel.target_ref == "malware--fedcba98-7654-3210-fedc-ba9876543210"
+    assert rel.source_ref == "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7"
+    assert rel.target_ref == "malware--9c4638ec-f1de-4ddb-abf4-1b760417654e"
diff --git a/stix2/test/v21/test_report.py b/stix2/test/v21/test_report.py
index d9e2d49..22aec2e 100644
--- a/stix2/test/v21/test_report.py
+++ b/stix2/test/v21/test_report.py
@@ -88,8 +88,8 @@ def test_report_example_objects_in_object_refs_with_bad_id():
 
     assert excinfo.value.cls == stix2.v21.Report
     assert excinfo.value.prop_name == "object_refs"
-    assert excinfo.value.reason == "must match <object-type>--<guid>."
-    assert str(excinfo.value) == "Invalid value for Report 'object_refs': must match <object-type>--<guid>."
+    assert excinfo.value.reason == stix2.properties.ERROR_INVALID_ID
+    assert str(excinfo.value) == "Invalid value for Report 'object_refs': " + stix2.properties.ERROR_INVALID_ID
 
 
 @pytest.mark.parametrize("data", [
diff --git a/stix2/test/v21/test_sighting.py b/stix2/test/v21/test_sighting.py
index baec1d9..79f3031 100644
--- a/stix2/test/v21/test_sighting.py
+++ b/stix2/test/v21/test_sighting.py
@@ -13,7 +13,7 @@ EXPECTED_SIGHTING = """{
     "id": "sighting--bfbc19db-ec35-4e45-beed-f8bde2a772fb",
     "created": "2016-04-06T20:06:37.000Z",
     "modified": "2016-04-06T20:06:37.000Z",
-    "sighting_of_ref": "indicator--01234567-89ab-cdef-0123-456789abcdef",
+    "sighting_of_ref": "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
     "where_sighted_refs": [
         "identity--8cc7afd6-5455-4d2b-a736-e614ee631d99"
     ]
@@ -23,7 +23,7 @@ BAD_SIGHTING = """{
     "created": "2016-04-06T20:06:37.000Z",
     "id": "sighting--bfbc19db-ec35-4e45-beed-f8bde2a772fb",
     "modified": "2016-04-06T20:06:37.000Z",
-    "sighting_of_ref": "indicator--01234567-89ab-cdef-0123-456789abcdef",
+    "sighting_of_ref": "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
     "spec_version": "2.1",
     "type": "sighting",
     "where_sighted_refs": [
@@ -87,8 +87,8 @@ def test_invalid_kwarg_to_sighting():
 def test_create_sighting_from_objects_rather_than_ids(malware):  # noqa: F811
     rel = stix2.v21.Sighting(sighting_of_ref=malware)
 
-    assert rel.sighting_of_ref == 'malware--00000000-0000-0000-0000-000000000001'
-    assert rel.id == 'sighting--00000000-0000-0000-0000-000000000003'
+    assert rel.sighting_of_ref == 'malware--00000000-0000-4000-8000-000000000001'
+    assert rel.id == 'sighting--00000000-0000-4000-8000-000000000003'
 
 
 @pytest.mark.parametrize("data", [
@@ -97,7 +97,7 @@ def test_create_sighting_from_objects_rather_than_ids(malware):  # noqa: F811
         "created": "2016-04-06T20:06:37Z",
         "id": "sighting--bfbc19db-ec35-4e45-beed-f8bde2a772fb",
         "modified": "2016-04-06T20:06:37Z",
-        "sighting_of_ref": "indicator--01234567-89ab-cdef-0123-456789abcdef",
+        "sighting_of_ref": "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
         "spec_version": "2.1",
         "type": "sighting",
         "where_sighted_refs": [
@@ -113,5 +113,5 @@ def test_parse_sighting(data):
     assert sighting.id == SIGHTING_ID
     assert sighting.created == dt.datetime(2016, 4, 6, 20, 6, 37, tzinfo=pytz.utc)
     assert sighting.modified == dt.datetime(2016, 4, 6, 20, 6, 37, tzinfo=pytz.utc)
-    assert sighting.sighting_of_ref == "indicator--01234567-89ab-cdef-0123-456789abcdef"
+    assert sighting.sighting_of_ref == "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7"
     assert sighting.where_sighted_refs == ["identity--8cc7afd6-5455-4d2b-a736-e614ee631d99"]
diff --git a/stix2/test/v21/test_utils.py b/stix2/test/v21/test_utils.py
index 8b368d3..1f8d8e2 100644
--- a/stix2/test/v21/test_utils.py
+++ b/stix2/test/v21/test_utils.py
@@ -98,8 +98,8 @@ def test_deduplicate(stix_objs1):
     ids = [obj['id'] for obj in unique]
     mods = [obj['modified'] for obj in unique]
 
-    assert "indicator--d81f86b8-975b-bc0b-775e-810c5ad45a4f" in ids
-    assert "indicator--d81f86b9-975b-bc0b-775e-810c5ad45a4f" in ids
+    assert "indicator--00000000-0000-4000-8000-000000000001" in ids
+    assert "indicator--00000000-0000-4000-8000-000000000001" in ids
     assert "2017-01-27T13:49:53.935Z" in mods
     assert "2017-01-27T13:49:53.936Z" in mods