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SQL Server Authentication Modes

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A fellow consultant here in Denver sent out a message yesterday inquiring about formal recommendations regarding the use of Windows Authentication vs. SQL Authentication. It seems that quite a few customers out there ponder these choices for a variety of reasons.

I dug up an email that I had sent to a different customer (that, for whatever reason, chooses to use SQL Authentication over Windows Autthentication):

From: Jeremy Jameson
To: [names removed to protect the innocent]
Subject: SQL Server Authentication Modes

Here is some info from MSDN:

SQL Server Authentication Modes

Microsoft® SQL Server™ can operate in one of two security (authentication) modes:

  • Windows Authentication Mode (Windows Authentication)
    Windows Authentication mode allows a user to connect through a Microsoft Windows NT® 4.0 or Windows® 2000 user account.
  • Mixed Mode (Windows Authentication and SQL Server Authentication)
  • Security Note  When possible, use Windows Authentication.

...

Windows Authentication has certain benefits over SQL Server Authentication, primarily due to its integration with the Windows NT 4.0 and Windows 2000 security system. Windows NT 4.0 and Windows 2000 security provides more features, such as secure validation and encryption of passwords, auditing, password expiration, minimum password length, and account lockout after multiple invalid login requests.

...

SQL Server Authentication is provided for backward compatibility because applications written for SQL Server version 7.0 or earlier may require the use of SQL Server logins and passwords. […]

...

Even though Windows Authentication is recommended, SQL Server Authentication may be required for connections with clients other than Windows NT 4.0 and Windows 2000 clients; it may also be necessary for legacy applications.

Pasted from <https://msdn.microsoft.com/library/en-us/adminsql/ad_security_47u6.asp?frame=true>

Windows authentication is more secure than SQL authentication for the following reasons:

  • Credentials are managed for you and the credentials are not transmitted over the network.
  • You avoid embedding user names and passwords in connection strings.
  • Logon security improves through password expiration periods, minimum lengths, and account lockout after multiple invalid logon requests. This mitigates the threat from dictionary attacks.

Pasted from <https://msdn.microsoft.com/practices/compcat/default.aspx?pull=/library/en-us/dnnetsec/html/SecNetch12.asp>

I remember speaking to a SQL Server Program Manager a few years ago at a session where he stated that as of SQL Server [2000] SP3 (and some specific version of MDAC which I don’t recall) the authentication between the client and SQL Server is automatically secured using SSL – assuming a trusted certificate is installed on the SQL Server. Perhaps that is the route that is being used here at Fabrikam [ed. actual customer name substituted]. In this case, the argument of sending credentials in clear text no longer applies. However, the storage of username/password in various config files is still valid regardless. Encrypting the credentials in the config files vastly improves the situation, but this will never be as secure as using Windows Authentication (primarily due to the increased security provided by standard protocols such as Kerberos).

Note that some improvements have been made in SQL Server 2005 (such as password expiration policies) that mitigate some of the items I mentioned in my original email. Nevertheless, if you have an Active Directory infrastructure in place -- which any organization over 2 people should ;-) -- and you are connecting from another server that you can get a valid Kerberos ticket on (i.e. in the same domain or in a trusted domain) then you should use Windows Authentication when connecting to SQL Server.

If you have the SQL Server in a separate domain (perhaps inside the corporate network but used by Web servers in the DMZ) then is it worth the effort to establish a cross-forest trust in order to be able to use Windows Authentication?

IMO, absolutely!

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