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Network security: Configure encryption types allowed for Kerberos

Published: November 15, 2012

Updated: November 15, 2012

Applies To: Windows 7, Windows 8, Windows 8.1, Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, Windows Vista



This security policy reference topic for the IT professional describes the best practices, location, values and security considerations for this policy setting.

This policy setting allows you to set the encryption types that the Kerberos protocol is allowed to use. If it is not selected, the encryption type will not be allowed. This setting might affect compatibility with client computers or services and applications. Multiple selections are permitted.

For more information, see article 977321 in the Microsoft Knowledge Base.

The following table lists and explains the allowed encryption types.

 

Encryption type Description and version support

DES_CBC_CRC

Data Encryption Standard with Cipher Block Chaining using the Cyclic Redundancy Check function

Supported in Windows 2000 Server, Windows XP, Windows Server 2003, Windows Vista, and Windows Server 2008. The Windows 7 and Windows Server 2008 R2 operating systems do not support DES by default.

DES_CBC_MD5

Data Encryption Standard with Cipher Block Chaining using the Message-Digest algorithm 5 checksum function

Supported in Windows 2000 Server, Windows XP, Windows Server 2003, Windows Vista, and Windows Server 2008. The Windows 7 and Windows Server 2008 R2 operating systems do not support DES by default.

RC4_HMAC_MD5

Rivest Cipher 4 with Hashed Message Authentication Code using the Message-Digest algorithm 5 checksum function

Supported in Windows 2000 Server, Windows XP, Windows Server 2003, Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2.

AES128_HMAC_SHA1

Advanced Encryption Standard in 128 bit cipher block with Hashed Message Authentication Code using the Secure Hash Algorithm (1).

Not supported in Windows 2000 Server, Windows XP, or Windows Server 2003. Supported in Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2.

AES256_HMAC_SHA1

Advanced Encryption Standard in 256 bit cipher block with Hashed Message Authentication Code using the Secure Hash Algorithm (1).

Not supported in Windows 2000 Server, Windows XP, or Windows Server 2003. Supported in Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2.

Future encryption types

Reserved by Microsoft for additional encryption types that might be implemented.

The encryption type options include:

  • DES_CBC_CRC

  • DES_CBC_MD5

  • RC4_HMAC_MD5

  • AES128_HMAC_SHA1

  • AES256_HMAC_SHA1

  • Future encryption types

    As of the release of Windows 7 and Windows Server 2008 R2, this is reserved by Microsoft for additional encryption types that might be implemented.

You must analyze your environment to determine which encryption types will be supported and then select those that meet that evaluation.

GPO_name \Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options

 

Server type or Group Policy Object (GPO) Default value

Default domain policy

Not defined

Default domain controller policy

Not defined

Stand-alone server default settings

Not defined

Domain controller effective default settings

None of these encryption types that are available in this policy are allowed.

Member server effective default settings

None of these encryption types that are available in this policy are allowed.

Effective GPO default settings on client computers

None of these encryption types that are available in this policy are allowed.

This policy was introduced in Windows Server 2008 R2 and Windows 7, and it can be applied to Windows operating systems beginning with Windows 2000.

This section describes how an attacker might exploit a feature or its configuration, how to implement the countermeasure, and the possible negative consequences of countermeasure implementation.

Windows Server 2008 R2 and Windows 7 do not support the DES cryptographic suites because stronger ones are available. To enable Kerberos interoperability with non-Windows versions of the Kerberos protocol, these suites can be enabled. However, doing so might open attack vectors on computers running Windows Server 2008 R2 and Windows 7. You can also disable DES for your computers running Windows Vista and Windows Server 2008.

Do not configure this policy. This will force the computers running Windows Server 2008 R2 and Windows 7 to use the AES or RC4 cryptographic suites.

If you do not select any of the encryption types, computers running Windows Server 2008 R2 and Windows 7 might have Kerberos authentication failures when connecting with computers running non-Windows versions of the Kerberos protocol.

If you do select any encryption type, you will lower the effectiveness of encryption for Kerberos authentication but you will improve interoperability with computers running older versions of Windows.

Contemporary non-Windows implementations of the Kerberos protocol support RC4 and AES 128-bit and AES 256-bit encryption. Most implementations, including the MIT Kerberos protocol and the Windows Kerberos protocol, are deprecating DES encryption.

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