diff --git a/moto/kms/models.py b/moto/kms/models.py
index 22f0039b2..32fcd23ae 100644
--- a/moto/kms/models.py
+++ b/moto/kms/models.py
@@ -7,13 +7,14 @@ from datetime import datetime, timedelta
 from boto3 import Session
 
 from moto.core import BaseBackend, BaseModel
+from moto.core.exceptions import JsonRESTError
 from moto.core.utils import iso_8601_datetime_without_milliseconds
-
+from moto.utilities.tagging_service import TaggingService
 from .utils import decrypt, encrypt, generate_key_id, generate_master_key
 
 
 class Key(BaseModel):
-    def __init__(self, policy, key_usage, description, tags, region):
+    def __init__(self, policy, key_usage, description, region):
         self.id = generate_key_id()
         self.policy = policy
         self.key_usage = key_usage
@@ -24,7 +25,6 @@ class Key(BaseModel):
         self.account_id = "012345678912"
         self.key_rotation_status = False
         self.deletion_date = None
-        self.tags = tags or {}
         self.key_material = generate_master_key()
 
     @property
@@ -70,11 +70,12 @@ class Key(BaseModel):
             policy=properties["KeyPolicy"],
             key_usage="ENCRYPT_DECRYPT",
             description=properties["Description"],
-            tags=properties.get("Tags"),
             region=region_name,
         )
         key.key_rotation_status = properties["EnableKeyRotation"]
         key.enabled = properties["Enabled"]
+        kms_backend.tag_resource(key.id, properties.get("Tags"))
+
         return key
 
     def get_cfn_attribute(self, attribute_name):
@@ -89,24 +90,19 @@ class KmsBackend(BaseBackend):
     def __init__(self):
         self.keys = {}
         self.key_to_aliases = defaultdict(set)
+        self.tagger = TaggingService(keyName='TagKey', valueName='TagValue')
 
     def create_key(self, policy, key_usage, description, tags, region):
-        key = Key(policy, key_usage, description, tags, region)
+        key = Key(policy, key_usage, description, region)
         self.keys[key.id] = key
+        if tags != None and len(tags) > 0:
+            self.tag_resource(key.id, tags)
         return key
 
     def update_key_description(self, key_id, description):
         key = self.keys[self.get_key_id(key_id)]
         key.description = description
 
-    def tag_resource(self, key_id, tags):
-        key = self.keys[self.get_key_id(key_id)]
-        key.tags = tags
-
-    def list_resource_tags(self, key_id):
-        key = self.keys[self.get_key_id(key_id)]
-        return key.tags
-
     def delete_key(self, key_id):
         if key_id in self.keys:
             if key_id in self.key_to_aliases:
@@ -282,6 +278,29 @@ class KmsBackend(BaseBackend):
 
         return plaintext, ciphertext_blob, arn
 
+    def list_resource_tags(self, key_id):
+        if key_id in self.keys:
+            return self.tagger.list_tags_for_resource(key_id)
+        raise JsonRESTError(
+            "NotFoundException", "The request was rejected because the specified entity or resource could not be found."
+        )
+
+    def tag_resource(self, key_id, tags):
+        if key_id in self.keys:
+            self.tagger.tag_resource(key_id, tags)
+            return {}
+        raise JsonRESTError(
+            "NotFoundException", "The request was rejected because the specified entity or resource could not be found."
+        )
+
+    def untag_resource(self, key_id, tag_names):
+        if key_id in self.keys:
+            self.tagger.untag_resource_using_names(key_id, tag_names)
+            return {}
+        raise JsonRESTError(
+            "NotFoundException", "The request was rejected because the specified entity or resource could not be found."
+        )
+
 
 kms_backends = {}
 for region in Session().get_available_regions("kms"):
diff --git a/moto/kms/responses.py b/moto/kms/responses.py
index d3a9726e1..3658f0d37 100644
--- a/moto/kms/responses.py
+++ b/moto/kms/responses.py
@@ -143,17 +143,27 @@ class KmsResponse(BaseResponse):
 
         self._validate_cmk_id(key_id)
 
-        self.kms_backend.tag_resource(key_id, tags)
-        return json.dumps({})
+        result = self.kms_backend.tag_resource(key_id, tags)
+        return json.dumps(result)
+
+    def untag_resource(self):
+        """https://docs.aws.amazon.com/kms/latest/APIReference/API_UntagResource.html"""
+        key_id = self.parameters.get("KeyId")
+        tag_names = self.parameters.get("TagKeys")
+
+        self._validate_cmk_id(key_id)
+
+        result = self.kms_backend.untag_resource(key_id, tag_names)
+        return json.dumps(result)
 
     def list_resource_tags(self):
         """https://docs.aws.amazon.com/kms/latest/APIReference/API_ListResourceTags.html"""
         key_id = self.parameters.get("KeyId")
-
         self._validate_cmk_id(key_id)
 
         tags = self.kms_backend.list_resource_tags(key_id)
-        return json.dumps({"Tags": tags, "NextMarker": None, "Truncated": False})
+        tags.update({"NextMarker": None, "Truncated": False})
+        return json.dumps(tags)
 
     def describe_key(self):
         """https://docs.aws.amazon.com/kms/latest/APIReference/API_DescribeKey.html"""
diff --git a/tests/test_kms/test_kms.py b/tests/test_kms/test_kms.py
index 70fa68787..6a35ee2c8 100644
--- a/tests/test_kms/test_kms.py
+++ b/tests/test_kms/test_kms.py
@@ -17,7 +17,8 @@ from boto.kms.exceptions import AlreadyExistsException, NotFoundException
 from freezegun import freeze_time
 from nose.tools import assert_raises
 from parameterized import parameterized
-
+from moto.core.exceptions import JsonRESTError
+from moto.kms.models import KmsBackend
 from moto.kms.exceptions import NotFoundException as MotoNotFoundException
 from moto import mock_kms, mock_kms_deprecated
 
@@ -910,36 +911,46 @@ def test_update_key_description():
     result = client.update_key_description(KeyId=key_id, Description="new_description")
     assert "ResponseMetadata" in result
 
+@mock_kms
+def test_key_tagging_happy():
+    client = boto3.client("kms", region_name="us-east-1")
+    key = client.create_key(Description="test-key-tagging")
+    key_id = key["KeyMetadata"]["KeyId"]
+
+    tags = [{"TagKey": "key1", "TagValue": "value1"}, {"TagKey": "key2", "TagValue": "value2"}]
+    client.tag_resource(KeyId=key_id, Tags=tags)
+
+    result = client.list_resource_tags(KeyId=key_id)
+    actual = result.get("Tags", [])
+    assert tags == actual
+
+    client.untag_resource(KeyId=key_id, TagKeys=["key1"])
+
+    actual = client.list_resource_tags(KeyId=key_id).get("Tags", [])
+    expected = [{"TagKey": "key2", "TagValue": "value2"}]
+    assert expected == actual
 
 @mock_kms
-def test_tag_resource():
-    client = boto3.client("kms", region_name="us-east-1")
-    key = client.create_key(Description="cancel-key-deletion")
-    response = client.schedule_key_deletion(KeyId=key["KeyMetadata"]["KeyId"])
+def test_key_tagging_sad():
+    b = KmsBackend()
 
-    keyid = response["KeyId"]
-    response = client.tag_resource(
-        KeyId=keyid, Tags=[{"TagKey": "string", "TagValue": "string"}]
-    )
+    try:
+        b.tag_resource('unknown', [])
+        raise 'tag_resource should fail if KeyId is not known'
+    except JsonRESTError:
+        pass
 
-    # Shouldn't have any data, just header
-    assert len(response.keys()) == 1
+    try:
+        b.untag_resource('unknown', [])
+        raise 'untag_resource should fail if KeyId is not known'
+    except JsonRESTError:
+        pass
 
-
-@mock_kms
-def test_list_resource_tags():
-    client = boto3.client("kms", region_name="us-east-1")
-    key = client.create_key(Description="cancel-key-deletion")
-    response = client.schedule_key_deletion(KeyId=key["KeyMetadata"]["KeyId"])
-
-    keyid = response["KeyId"]
-    response = client.tag_resource(
-        KeyId=keyid, Tags=[{"TagKey": "string", "TagValue": "string"}]
-    )
-
-    response = client.list_resource_tags(KeyId=keyid)
-    assert response["Tags"][0]["TagKey"] == "string"
-    assert response["Tags"][0]["TagValue"] == "string"
+    try:
+        b.list_resource_tags('unknown')
+        raise 'list_resource_tags should fail if KeyId is not known'
+    except JsonRESTError:
+        pass
 
 
 @parameterized(
diff --git a/tests/test_kms/test_utils.py b/tests/test_kms/test_utils.py
index f5478e0ef..29ea969b5 100644
--- a/tests/test_kms/test_utils.py
+++ b/tests/test_kms/test_utils.py
@@ -102,7 +102,7 @@ def test_deserialize_ciphertext_blob(raw, serialized):
 @parameterized(((ec[0],) for ec in ENCRYPTION_CONTEXT_VECTORS))
 def test_encrypt_decrypt_cycle(encryption_context):
     plaintext = b"some secret plaintext"
-    master_key = Key("nop", "nop", "nop", [], "nop")
+    master_key = Key("nop", "nop", "nop", "nop")
     master_key_map = {master_key.id: master_key}
 
     ciphertext_blob = encrypt(
@@ -133,7 +133,7 @@ def test_encrypt_unknown_key_id():
 
 
 def test_decrypt_invalid_ciphertext_format():
-    master_key = Key("nop", "nop", "nop", [], "nop")
+    master_key = Key("nop", "nop", "nop", "nop")
     master_key_map = {master_key.id: master_key}
 
     with assert_raises(InvalidCiphertextException):
@@ -153,7 +153,7 @@ def test_decrypt_unknwown_key_id():
 
 
 def test_decrypt_invalid_ciphertext():
-    master_key = Key("nop", "nop", "nop", [], "nop")
+    master_key = Key("nop", "nop", "nop", "nop")
     master_key_map = {master_key.id: master_key}
     ciphertext_blob = (
         master_key.id.encode("utf-8") + b"123456789012"
@@ -171,7 +171,7 @@ def test_decrypt_invalid_ciphertext():
 
 def test_decrypt_invalid_encryption_context():
     plaintext = b"some secret plaintext"
-    master_key = Key("nop", "nop", "nop", [], "nop")
+    master_key = Key("nop", "nop", "nop", "nop")
     master_key_map = {master_key.id: master_key}
 
     ciphertext_blob = encrypt(