What is SMB Signing?
Server Message Block (SMB) is the protocol used for CIFS file sharing and other communications between Windows computers. SMB signing is a method to prevent man-in-the-middle attacks from tampering with CIFS content. The decision to use SMB signing is negotiated between the Client and Server, and relies on a shared secret based on the user’s authenticated data to create a digital signature in the SMB header. All subsequent SMB calls for that transaction continue to rely on the signed header to guarantee that content transferred over CIFS has not been altered. Since SMB signing is negotiated, whether or not signing occurs depends on the Windows settings on both the Client and Servers. For Windows 2000, XP, and 2003, there are four possible option settings. Two of these options control the behavior of the client, and the other two are for the behavior when acting as a server. These can be configured from the Group or Security Options Policy.
