Key Management Server

Key Management Server (KM Server) is an optional Microsoft Exchange Server component that is installed on a designated organization server. It provides centralized administration, archival of private keys, management of public keys and certificates, and it is used to set up an advanced security system.

The KM server performs a variety of important tasks:

• Generates public and private encryption keys.
• Acts as your CA by creating public signing and encryption X.509 certificates. After the KM server has generated keys and certificates and the user's security file has been created, the KM server doesn't need to be running for a user to send and receive encrypted and signed messages, because your client actually performs all of the security operations on messages.
• Maintains a secure copy of every user's private encryption key in an encrypted database in case the key needs to be retrieved after it has been issued. For example, if a user is terminated or leaves the company, the KM server enables an authorized administrator to recover the user's encrypted messages by recovering the user's private keys. You can also recover keys for users when they lose their security (.epf) file or their registry setting, or if they forget their security file password.
• Maintains and distributes a certificate revocation list (CRL). The CRL is a list of certificates that the administrator has recovered because the user's keys have been compromised and are no longer secure. It is stored in the directory on every server. A replica of the revocation list is also kept on the client computer so that certificates can be checked when the user is working offline. When you decrypt a message or verify its signature, the revocation list is checked to make sure the certificate has not been revoked. If it has, the user is warned that the sender has been revoked from the organization. For more information about certificate revocation, see Microsoft Exchange Server Concepts and Planning.