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What is Local Security Authority?
This question posed on 28 June 2001
The Local Security Authority or LSA is a key component of the logon process in both Windows NT and Windows 2000. In Windows 2000, the LSA is responsible for validating users for both local and remote logons. The LSA also maintains the local security policy.
During the local (interactive) logon to a machine, a person enters their name and password to the logon dialog. This information is passed to the LSA, which then calls the appropriate authentication package. The password is sent in a nonreversible secret key format using a one-way hash function. The LSA then queries the SAM database for the user's account information. If the key provided matches the one in the SAM, the SAM returns the users SID and the SIDs of any groups the user belongs to. The LSA then uses these SIDs to generate the security access token.
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What is the function of the SID?
This question posed on 15 July 2003
Security identifier (SID) is a unique security identification number assigned to security principals (objects that can be assigned access to objects in Windows). Users, groups and computers are assigned SIDs. This uniquely identifies the user group or computer to the domain or to the local computer if a local account is used. For example, when a user logs on a collection of his SID, the SIDs of groups of which he is a member is made. This list is used when he needs to access a resource -- say, a file. The file has a Discretionary Access List (DACL) that is composed of access control entries (ACE) that include a SID and what permission that SID has on the file. The DACL is checked against the user's list, and a decision can be made whether or not to let him access the file.