LAN Manager

LAN ManagerDeveloper| Microsoft, 3Com

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OS family| OS/2
Working state| Discontinued
Source model| Closed source
Initial release| 1987; 39 years ago (1987)
Yes|Final release|Latest release}}| 2.2a / 1994; 32 years ago (1994)
Marketing target| Local area networking
Update method| Re-installation
Package manager| None
Platforms| x86
License| Proprietary
Preceded by| MS-Net, Xenix-NET, 3+Share
Succeeded by| Microsoft Windows NT 3.1

LAN Manager is a discontinued network operating system (NOS) available from multiple vendors and developed by Microsoft in cooperation with 3Com Corporation. It was designed to succeed 3Com's 3+Share network server software which ran atop a heavily modified version of MS-DOS.

## Contents

* 1 History
* 1.1 Versions
* 2 Password hashing algorithm
* 3 Security weaknesses
* 4 Workarounds
* 5 Reasons for continued use of LM hash
* 6 See also
* 7 Notes
* 8 References
* 9 External links

## History

The LAN Manager OS/2 operating system was co-developed by IBM and Microsoft, using the Server Message Block (SMB) protocol. It originally used SMB atop either the NetBIOS Frames (NBF) protocol or a specialized version of the Xerox Network Systems (XNS) protocol. These legacy protocols had been inherited from previous products such as MS-Net for MS-DOS, Xenix-NET for MS-Xenix, and the afore-mentioned 3+Share. A version of LAN Manager for Unix-based systems called LAN Manager/X was also available. LAN Manager/X was the basis for Digital Equipment Corporation's Pathworks product for OpenVMS, Ultrix and Tru64.[1]

Despite support from 3Com, IBM, Digital, and Digital Communications Associates, PC wrote in 1989, LAN Manager "has made a very small impression on the market and continues to receive the cold shoulder from buyers" compared to Novell NetWare. The combined companies "pose a strong potential threat", however, the magazine added.[2] In 1990, Microsoft announced LAN Manager 2.0 with a host of improvements, including support for TCP/IP as a transport protocol for SMB, using NetBIOS over TCP/IP (NBT). The last version of LAN Manager, 2.2, which included an MS-OS/2 1.31 base operating system, remained Microsoft's strategic server system until the release of Windows NT Advanced Server in 1993.[3]

### Versions

* 1987 – MS LAN Manager 1.0 (Basic/Enhanced)
* 1989 – MS LAN Manager 1.1
* 1991 – MS LAN Manager 2.0
* 1992 – MS LAN Manager 2.1
* 1992 – MS LAN Manager 2.1a
* 1993 – MS LAN Manager 2.2
* 1994 – MS LAN Manager 2.2a

Many vendors shipped licensed versions, including:

* 3Com Corporation 3+Open
* HP LAN Manager/X
* IBM LAN Server
* Tapestry Torus
* The Santa Cruz Operation

## Password hashing algorithm

The LM hash is computed as follows:[4][5]

1. The user's password is restricted to a maximum of fourteen characters.[Notes 1]
2. The user's password is converted to uppercase.
3. The user's password is encoded in the System OEM code page.[6]
4. This password is NULL-padded to 14 bytes.[7]
5. The “fixed-length” password is split into two 7-byte halves.
6. These values are used to create two DES keys, one from each 7-byte half, by converting the seven bytes into a bit stream with the most significant bit first, and inserting a parity bit after every seven bits (so `1010100` becomes `10101000`). This generates the 64 bits needed for a DES key. (A DES key ostensibly consists of 64 bits; however, only 56 of these are actually used by the algorithm. The parity bits added in this step are later discarded.)
7. Each of the two keys is used to DES-encrypt the constant ASCII string “`KGS!@#$%`”,[Notes 2] resulting in two 8-byte ciphertext values. The DES CipherMode should be set to ECB, and PaddingMode should be set to `NONE`.
8. These two ciphertext values are concatenated to form a 16-byte value, which is the LM hash.

## Security weaknesses

LAN Manager authentication uses a particularly weak method of hashing a user's password known as the LM hash algorithm, stemming from the mid-1980s when viruses transmitted by floppy disks were the major concern.[8] Although it is based on DES, a well-studied block cipher, the LM hash has several weaknesses in its design.[9] This makes such hashes crackable in a matter of seconds using rainbow tables, or in a few minutes using brute force. Starting with Windows NT, it was replaced by NTLM, which is still vulnerable to rainbow tables, and brute force attacks unless long, unpredictable passwords are used, see password cracking. NTLM is used for logon with local accounts except on domain controllers since Windows Vista and later versions no longer maintain the LM hash by default.[8] Kerberos is used in Active Directory Environments.

The major weaknesses of LAN Manager authentication protocol are:[10]

1. Password length is limited to a maximum of 14 characters chosen from the 95 ASCII printable characters.
2. Passwords are not case sensitive. All passwords are converted into uppercase before generating the hash value. Hence LM hash treats PassWord, password, PaSsWoRd, PASSword and other similar combinations same as PASSWORD. This practice effectively reduces the LM hash key space to 69 characters.
3. A 14-character password is broken into 7+7 characters and the hash is calculated for each half separately. This way of calculating the hash makes it dramatically easier to crack, as the attacker only needs to brute-force 7 characters twice instead of the full 14 characters. This makes the effective strength of a 14-character password equal to only 2×697≈244, or twice that of a 7-character password, which is 3.7 trillion times less complex than the 6914≈286 theoretical strength of a 14-character single-case password. As of 2020, a computer equipped with a high-end graphics processor (GPUs) can compute 40 billion LM-hashes per second.[11] At that rate, all 7-character passwords from the 95-character set can be tested and broken in half an hour; all 7-character alphanumeric passwords can be tested and broken in 2 seconds.
4. If the password is 7 characters or less, then the second half of hash will always produce same constant value (0xAAD3B435B51404EE). Therefore, a password is less than or equal to 7 characters long can be identified visibly without using tools (though with high speed GPU attacks, this matters less).
5. The hash value is sent to network servers without salting, making it susceptible to man-in-the-middle attacks such as replay the hash. Without salt, time–memory tradeoff pre-computed dictionary attacks, such as a rainbow table, are feasible. In 2003, Ophcrack, an implementation of the rainbow table technique, was published. It specifically targets the weaknesses of LM encryption, and includes pre-computed data sufficient to crack virtually all alphanumeric LM hashes in a few seconds. Many cracking tools, such as RainbowCrack, Hashcat, L0phtCrack and Cain, now incorporate similar attacks and make cracking of LM hashes fast and trivial.

## Workarounds

To address the security weaknesses inherent in LM encryption and authentication schemes, Microsoft introduced the NTLMv1 protocol in 1993 with Windows NT 3.1. For hashing, NTLM uses Unicode support, replacing `LMhash=DESeach(DOSCHARSET(UPPERCASE(password)), "KGS!@#$%")` by `NThash=MD4(UTF-16-LE(password))`, which does not require any padding or truncating that would simplify the key. On the negative side, the same DES algorithm was used with only 56-bit encryption for the subsequent authentication steps, and there is still no salting. Furthermore, Windows machines were for many years configured by default to send and accept responses derived from both the LM hash and the NTLM hash, so the use of the NTLM hash provided no additional security while the weaker hash was still present. It also took time for artificial restrictions on password length in management tools such as User Manager to be lifted.

While LAN Manager is considered obsolete and current Windows operating systems use the stronger NTLMv2 or Kerberos authentication methods, Windows systems before Windows Vista/Windows Server 2008 enabled the LAN Manager hash by default for backward compatibility with legacy LAN Manager and Windows ME or earlier clients, or legacy NetBIOS-enabled applications. It has for many years been considered good security practice to disable the compromised LM and NTLMv1 authentication protocols where they aren't needed.[12]

## Reasons for continued use of LM hash

Many legacy third party SMB implementations have taken considerable time to add support for the stronger protocols that Microsoft has created to replace LM hashing because the open source communities supporting these libraries first had to reverse engineer the newer protocols—Samba took 5 years to add NTLMv2 support, while JCIFS took 10 years.

Availability of NTLM protocols to replace LM authentication  Product  | NTLMv1 support  | NTLMv2 support

|
|

Windows NT 3.1 | RTM (1993)  | Not supported
Windows NT 3.5 | RTM (1994)  | Not supported
Windows NT 3.51 | RTM (1995)  | Not supported
Windows NT 4  | RTM (1996)  | Service Pack 4[13] (October 25, 1998)
Windows 95 | Not supported  | Directory services client (released with Windows 2000 Server, February 17, 2000)
Windows 98 | RTM  | Directory services client (released with Windows 2000 Server, February 17, 2000)
Windows 2000 | RTM (February 17, 2000)  | RTM (February 17, 2000)
Windows Me | RTM (September 14, 2000)  | Directory services client (released with Windows 2000 Server, February 17, 2000)
Samba | ?  | Version 3.0[14] (September 24, 2003)
JCIFS  | Not supported  | Version 1.3.0 (October 25, 2008)[15]
IBM AIX (SMBFS)  | 5.3 (2004)[16] | Not supported as of v7.1[17]

Poor patching regimes subsequent to software releases supporting the feature becoming available have contributed to some organisations continuing to use LM Hashing in their environments, even though the protocol is easily disabled in Active Directory itself.

Lastly, prior to the release of Windows Vista, many unattended build processes still used a DOS boot disk (instead of Windows PE) to start the installation of Windows using WINNT.EXE, something that requires LM hashing to be enabled for the legacy LAN Manager networking stack to work.

## See also

* NT LAN Manager
* Active Directory
* Password cracking
* Dictionary attack
* Remote Program Load (RPL)
* Security Account Manager

## Notes

1. ↑ If the password is more than fourteen characters long, the LM hash cannot be computed.
2. ↑ The string “KGS!@#$%” could possibly mean Key of Glen and Steve and then the combination of Shift + 12345. Glen Zorn and Steve Cobb are the authors of RFC 2433 (Microsoft PPP CHAP Extensions).

## References

1. ↑ Andy Goldstein (2005). "Samba and OpenVMS". http://de.openvms.org/TUD2005/02_Advanced_Server_and_Samba_Andy_Goldstein.pdf.
2. ↑ Derfler, Frank J. Jr.; Thompson, M. Keith (1989-12-12). "Novell's NetWare 386". PC Magazine 8 (21): 205. https://books.google.com/books?id=5CmkZ3THZtwC&pg=PT206. Retrieved 2025-05-02.
3. ↑ "DOS SMB Client Performance | OS/2 Museum" (in en-US). https://www.os2museum.com/wp/dos-smb-client-performance/.
4. ↑ "Chapter 3 - Operating System Installation". Microsoft Docs. March 24, 2009. The LMHash. https://learn.microsoft.com/previous-versions/tn-archive/dd277300(v=technet.10)#the-lmhash.
5. ↑ Glass, Eric (2006). "The NTLM Authentication Protocol and Security Support Provider: The LM Response". https://davenport.sourceforge.net/ntlm.html#theLmResponse.
6. ↑ "List of Localized MS Operating Systems". Microsoft Developer Network. https://msdn.microsoft.com/nl-nl/goglobal/cc563921(en-us).aspx.
7. ↑ "Cluster service account password must be set to 15 or more characters if the NoLMHash policy is enabled". Microsoft. October 30, 2006. https://support.microsoft.com/kb/828861.
8. ↑ 8.0 8.1 "The Most Misunderstood Windows Security Setting of All Time". Microsoft. August 31, 2016. https://learn.microsoft.com/en-us/previous-versions/technet-magazine/cc160954(v=msdn.10). "Although Windows Vista has not been released yet, it is worthwhile to point out some changes in this operating system related to these protocols. The most important change is that the LM protocol can no longer be used for inbound authentication—where Windows Vista is acting as the authentication server."
9. ↑ Johansson, Jasper M. (June 29, 2004). "Windows Passwords: Everything You Need To Know". Microsoft. http://download.microsoft.com/download/f/4/a/f4a67fc8-c499-461d-a025-8155fb4f7a0f/Windows Passwords Master 1.5 Handout - Jesper Johansson.ppt.
10. ↑ Rahul Kokcha
11. ↑ Benchmark Hashcat v6.1.1 on RTX 2070S (SUPER), Mode 3000 LM, accessed November 29, 2020
12. ↑ "How to prevent Windows from storing a LAN manager hash of your password in Active Directory and local SAM databases". Microsoft Docs. December 3, 2007. https://learn.microsoft.com/en-US/troubleshoot/windows-server/windows-security/prevent-windows-store-lm-hash-password.
13. ↑ "Windows NT 4.0 Service Pack 4 Readme.txt File (40-bit)". Microsoft. October 25, 1998. https://support.microsoft.com/kb/194507.
14. ↑ "The Samba Team announces the first official release of Samba 3.0". SAMBA. September 24, 2003. https://www.samba.org/samba/history/samba-3.0.0.html.
15. ↑ "The Java CIFS Client Library". https://jcifs.samba.org/.
16. ↑ "AIX 5.3 Networks and communication management: Server Message Block file system". IBM. March 15, 2010. p. 441. http://www-01.ibm.com/support/knowledgecenter/ssw_aix_53/com.ibm.aix.commadmn/doc/commadmndita/smbfs_intro.htm.
17. ↑ "AIX 7.1 Networks and communication management: Server Message Block file system". IBM. December 5, 2011. http://www-01.ibm.com/support/knowledgecenter/ssw_aix_71/com.ibm.aix.networkcomm/smbfs_intro.htm.

## External links

| Wikibooks has a book on the topic of: Reverse Engineering/Cracking Windows XP Passwords

|

*   * "Microsoft LAN Manager User's Guide for MS-DOS". https://bitsavers.org/pdf/dec/decnet/pathworks_DOS/AA-PHH1A-TK_Pathworks_for_DOS_Microsoft_LAN_Manager_Users_Guide_for_MS-DOS_1990.pdf.

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