---
title: Policy CSP - Kerberos
description: Define the list of trusting forests that the Kerberos client searches when attempting to resolve two-part service principal names (SPNs).
ms.author: dansimp
ms.topic: article
ms.prod: w10
ms.technology: windows
author: manikadhiman
ms.localizationpriority: medium
ms.date: 09/27/2019
ms.reviewer: 
manager: dansimp
---

# Policy CSP - Kerberos


<hr/>

<!--Policies-->
## Kerberos policies  

<dl>
  <dd>
    <a href="#kerberos-allowforestsearchorder">Kerberos/AllowForestSearchOrder</a>
  </dd>
  <dd>
    <a href="#kerberos-kerberosclientsupportsclaimscompoundarmor">Kerberos/KerberosClientSupportsClaimsCompoundArmor</a>
  </dd>
  <dd>
    <a href="#kerberos-pkinithashalgorithmconfiguration">Kerberos/PKInitHashAlgorithmConfiguration</a>
  </dd>
  <dd>
    <a href="#kerberos-requirekerberosarmoring">Kerberos/RequireKerberosArmoring</a>
  </dd>
  <dd>
    <a href="#kerberos-requirestrictkdcvalidation">Kerberos/RequireStrictKDCValidation</a>
  </dd>
  <dd>
    <a href="#kerberos-setmaximumcontexttokensize">Kerberos/SetMaximumContextTokenSize</a>
  </dd>
  <dd>
    <a href="#kerberos-upnnamehints">Kerberos/UPNNameHints</a>
  </dd>
</dl>

> [!TIP]
> These are ADMX-backed policies and require a special SyncML format to enable or disable.  For details, see [Understanding ADMX-backed policies](./understanding-admx-backed-policies.md).
> 
> You must specify the data type in the SyncML as &lt;Format&gt;chr&lt;/Format&gt;. For an example SyncML, refer to [Enabling a policy](./understanding-admx-backed-policies.md#enabling-a-policy).
> 
> The payload of the SyncML must be XML-encoded; for this XML encoding, there are a variety of online encoders that you can use. To avoid encoding the payload, you can use CDATA if your MDM supports it.  For more information, see [CDATA Sections](http://www.w3.org/TR/REC-xml/#sec-cdata-sect).


<hr/>

<!--Policy-->
<a href="" id="kerberos-allowforestsearchorder"></a>**Kerberos/AllowForestSearchOrder**  

<!--SupportedSKUs-->
<table>
<tr>
    <th>Edition</th>
    <th>Windows 10</th>
    <th>Windows 11</th>
</tr>
<tr>
    <td>Home</td>
    <td>No</td>
    <td>No</td>
</tr>
<tr>
    <td>Pro</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
<tr>
    <td>Business</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
<tr>
    <td>Enterprise</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
<tr>
    <td>Education</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
</table>

<!--/SupportedSKUs-->
<hr/>

<!--Scope-->
[Scope](./policy-configuration-service-provider.md#policy-scope):

> [!div class = "checklist"]
> * Device

<hr/>

<!--/Scope-->
<!--Description-->
This policy setting defines the list of trusting forests that the Kerberos client searches when attempting to resolve two-part service principal names (SPNs).

If you enable this policy setting, the Kerberos client searches the forests in this list, if it is unable to resolve a two-part SPN. If a match is found, the Kerberos client requests a referral ticket to the appropriate domain.

If you disable or do not configure this policy setting, the Kerberos client does not search the listed forests to resolve the SPN. If the Kerberos client is unable to resolve the SPN because the name is not found, NTLM authentication might be used.

<!--/Description-->

<!--ADMXBacked-->
ADMX Info:  
-   GP Friendly name: *Use forest search order*
-   GP name: *ForestSearch*
-   GP path: *System/Kerberos*
-   GP ADMX file name: *Kerberos.admx*

<!--/ADMXBacked-->
<!--/Policy-->

<hr/>

<!--Policy-->
<a href="" id="kerberos-kerberosclientsupportsclaimscompoundarmor"></a>**Kerberos/KerberosClientSupportsClaimsCompoundArmor**  

<!--SupportedSKUs-->
<table>
<tr>
    <th>Edition</th>
    <th>Windows 10</th>
    <th>Windows 11</th>
</tr>
<tr>
    <td>Home</td>
    <td>No</td>
    <td>No</td>
</tr>
<tr>
    <td>Pro</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
<tr>
    <td>Business</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
<tr>
    <td>Enterprise</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
<tr>
    <td>Education</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
</table>

<!--/SupportedSKUs-->
<hr/>

<!--Scope-->
[Scope](./policy-configuration-service-provider.md#policy-scope):

> [!div class = "checklist"]
> * Device

<hr/>

<!--/Scope-->
<!--Description-->
This policy setting controls whether a device will request claims and compound authentication for Dynamic Access Control and Kerberos armoring using Kerberos authentication with domains that support these features. 
If you enable this policy setting, the client computers will request claims, provide information required to create compounded authentication and armor Kerberos messages in domains which support claims and compound authentication for Dynamic Access Control and Kerberos armoring.

If you disable or do not configure this policy setting, the client devices will not request claims, provide information required to create compounded authentication and armor Kerberos messages. Services hosted on the device will not be able to retrieve claims for clients using Kerberos protocol transition.

<!--/Description-->

<!--ADMXBacked-->
ADMX Info:  
-   GP Friendly name: *Kerberos client support for claims, compound authentication and Kerberos armoring*
-   GP name: *EnableCbacAndArmor*
-   GP path: *System/Kerberos*
-   GP ADMX file name: *Kerberos.admx*

<!--/ADMXBacked-->
<!--/Policy-->

<hr/>

<!--Policy-->
<a href="" id="kerberos-pkinithashalgorithmconfiguration"></a>**Kerberos/PKInitHashAlgorithmConfiguration**  

<!--SupportedSKUs-->
<table>
<tr>
    <th>Edition</th>
    <th>Windows 10</th>
    <th>Windows 11</th>
</tr>
<tr>
    <td>Home</td>
    <td>No</td>
    <td>No</td>
</tr>
<tr>
    <td>Pro</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
<tr>
    <td>Business</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Enterprise</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
<tr>
    <td>Education</td>
    <td>Yes</td>
    <td>Yes</td>
</tr>
</table>

<!--/SupportedSKUs-->
<hr/>

<!--Scope-->
[Scope](./policy-configuration-service-provider.md#policy-scope):

> [!div class = "checklist"]
> * Device

<hr/>

<!--/Scope-->
<!--Description-->

This policy setting controls hash or checksum algorithms used by the Kerberos client when performing certificate authentication.

If you enable this policy, you will be able to configure one of four states for each algorithm:

* **Default**: This sets the algorithm to the recommended state.
* **Supported**: This enables usage of the algorithm. Enabling algorithms that have been disabled by default may reduce your security.
* **Audited**: This enables usage of the algorithm and reports an event (ID 205) every time it is used. This state is intended to verify that the algorithm is not being used and can be safely disabled.
* **Not Supported**: This disables usage of the algorithm. This state is intended for algorithms that are deemed to be insecure.

If you disable or do not configure this policy, each algorithm will assume the **Default** state.

More information about the hash and checksum algorithms supported by the Windows Kerberos client and their default states can be found https://go.microsoft.com/fwlink/?linkid=2169037.

<!--/Description-->

<!--ADMXBacked-->
ADMX Info:  
-   GP Friendly name: *Introducing agility to PKINIT in Kerberos protocol*
-   GP name: *PKInitHashAlgorithmConfiguration*
-   GP path: *System/Kerberos*
-   GP ADMX file name: *Kerberos.admx*

<!--/ADMXBacked-->
<!--/Policy-->

<hr/>

<!--Policy-->
<a href="" id="kerberos-requirekerberosarmoring"></a>**Kerberos/RequireKerberosArmoring**  

<!--SupportedSKUs-->
<table>
<tr>
    <th>Edition</th>
    <th>Windows 10</th>
    <th>Windows 11</th>
</tr>
<tr>
    <td>Home</td>
    <td>No</td>
    <td>No</td>
</tr>
<tr>
    <td>Pro</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Business</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Enterprise</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Education</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
</table>

<!--/SupportedSKUs-->
<hr/>

<!--Scope-->
[Scope](./policy-configuration-service-provider.md#policy-scope):

> [!div class = "checklist"]
> * Device

<hr/>

<!--/Scope-->
<!--Description-->
This policy setting controls whether a computer requires that Kerberos message exchanges be armored when communicating with a domain controller.

Warning: When a domain does not support Kerberos armoring by enabling "Support Dynamic Access Control and Kerberos armoring", then all authentication for all its users will fail from computers with this policy setting enabled.

If you enable this policy setting, the client computers in the domain enforce the use of Kerberos armoring in only authentication service (AS) and ticket-granting service (TGS) message exchanges with the domain controllers. 

> [!NOTE]
> The Kerberos Group Policy "Kerberos client support for claims, compound authentication and Kerberos armoring" must also be enabled to support Kerberos armoring. 

If you disable or do not configure this policy setting, the client computers in the domain enforce the use of Kerberos armoring when possible as supported by the target domain.

<!--/Description-->

<!--ADMXBacked-->
ADMX Info:  
-   GP Friendly name: *Fail authentication requests when Kerberos armoring is not available*
-   GP name: *ClientRequireFast*
-   GP path: *System/Kerberos*
-   GP ADMX file name: *Kerberos.admx*

<!--/ADMXBacked-->
<!--/Policy-->

<hr/>

<!--Policy-->
<a href="" id="kerberos-requirestrictkdcvalidation"></a>**Kerberos/RequireStrictKDCValidation**  

<!--SupportedSKUs-->
<table>
<tr>
    <th>Edition</th>
    <th>Windows 10</th>
    <th>Windows 11</th>
</tr>
<tr>
    <td>Home</td>
    <td>No</td>
    <td>No</td>
</tr>
<tr>
    <td>Pro</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Business</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Enterprise</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Education</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
</table>

<!--/SupportedSKUs-->
<hr/>

<!--Scope-->
[Scope](./policy-configuration-service-provider.md#policy-scope):

> [!div class = "checklist"]
> * Device

<hr/>

<!--/Scope-->
<!--Description-->
This policy setting controls the Kerberos client's behavior in validating the KDC certificate for smart card and system certificate logon.  

If you enable this policy setting, the Kerberos client requires that the KDC's X.509 certificate contains the KDC key purpose object identifier in the Extended Key Usage (EKU) extensions, and that the KDC's X.509 certificate contains a dNSName subjectAltName (SAN) extension that matches the DNS name of the domain. If the computer is joined to a domain, the Kerberos client requires that the KDC's X.509 certificate must be signed by a Certificate Authority (CA) in the NTAuth store. If the computer is not joined to a domain, the Kerberos client allows the root CA certificate on the smart card to be used in the path validation of the KDC's X.509 certificate.

If you disable or do not configure this policy setting, the Kerberos client requires only that the KDC certificate contain the Server Authentication purpose object identifier in the EKU extensions which can be issued to any server.

<!--/Description-->

<!--ADMXBacked-->
ADMX Info:  
-   GP Friendly name: *Require strict KDC validation*
-   GP name: *ValidateKDC*
-   GP path: *System/Kerberos*
-   GP ADMX file name: *Kerberos.admx*

<!--/ADMXBacked-->
<!--/Policy-->

<hr/>

<!--Policy-->
<a href="" id="kerberos-setmaximumcontexttokensize"></a>**Kerberos/SetMaximumContextTokenSize**  

<!--SupportedSKUs-->
<table>
<tr>
    <th>Edition</th>
    <th>Windows 10</th>
    <th>Windows 11</th>
</tr>
<tr>
    <td>Home</td>
    <td>No</td>
    <td>No</td>
</tr>
<tr>
    <td>Pro</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Business</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Enterprise</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Education</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
</table>

<!--/SupportedSKUs-->
<hr/>

<!--Scope-->
[Scope](./policy-configuration-service-provider.md#policy-scope):

> [!div class = "checklist"]
> * Device

<hr/>

<!--/Scope-->
<!--Description-->
This policy setting allows you to set the value returned to applications which request the maximum size of the SSPI context token buffer size.

The size of the context token buffer determines the maximum size of SSPI context tokens an application expects and allocates. Depending upon authentication request processing and group memberships, the buffer might be smaller than the actual size of the SSPI context token. 

If you enable this policy setting, the Kerberos client or server uses the configured value, or the locally allowed maximum value, whichever is smaller.

If you disable or do not configure this policy setting, the Kerberos client or server uses the locally configured value or the default value. 

> [!NOTE]
> This policy setting configures the existing MaxTokenSize registry value in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters, which was added in Windows XP and Windows Server 2003, with a default value of 12,000 bytes. Beginning with Windows 8 the default is 48,000 bytes. Due to HTTP's base64 encoding of authentication context tokens, it is not advised to set this value more than 48,000 bytes.

<!--/Description-->

<!--ADMXBacked-->
ADMX Info:  
-   GP Friendly name: *Set maximum Kerberos SSPI context token buffer size*
-   GP name: *MaxTokenSize*
-   GP path: *System/Kerberos*
-   GP ADMX file name: *Kerberos.admx*

<!--/ADMXBacked-->
<!--/Policy-->

<hr/>

<!--Policy-->
<a href="" id="kerberos-upnnamehints"></a>**Kerberos/UPNNameHints**  

<!--SupportedSKUs-->
<table>
<tr>
    <th>Edition</th>
    <th>Windows 10</th>
    <th>Windows 11</th>
</tr>
<tr>
    <td>Home</td>
    <td>No</td>
    <td>No</td>
</tr>
<tr>
    <td>Pro</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Business</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Enterprise</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
<tr>
    <td>Education</td>
     <td>Yes</td>
     <td>Yes</td>
</tr>
</table>

<!--/SupportedSKUs-->
<hr/>

<!--Scope-->
[Scope](./policy-configuration-service-provider.md#policy-scope):

> [!div class = "checklist"]
> * Device

<hr/>

<!--/Scope-->
<!--Description-->
Adds a list of domains that an Azure Active Directory joined device can attempt to contact when it cannot resolve a UPN to a principal.

Devices joined to Azure Active Directory in a hybrid environment need to interact with Active Directory Domain Controllers, but they lack the built-in ability to find a Domain Controller that a domain-joined device has. This can cause failures when such a device needs to resolve an Azure Active Directory UPN into an Active Directory Principal. You can use this policy to avoid those failures.

<!--/Description-->
<!--SupportedValues-->

<!--/SupportedValues-->
<!--Example-->

<!--/Example-->
<!--Validation-->

<!--/Validation-->
<!--/Policy-->
<hr/>

<!--/Policies-->