Storing Information on the Server in Secure RPC

After the server decrypts the client's timestamp, the server stores four items of information in a credential table:

• The client's computer name

• The conversation key

• The window

• The client's timestamp

The server stores the first three items for future use. The server stores the client's timestamp to protect against replays. The server accepts only timestamps that are chronologically greater than the last timestamp seen. As a result, any replayed transactions are guaranteed to be rejected.

Implicit in these transactions is the name of the caller, who must be authenticated in some manner. The keyserver cannot use DES authentication to authenticate the caller because the use of DES by the keyserver would create a deadlock. To avoid a deadlock, the keyserver stores the secret keys by user ID (UID) and grants requests only to local root processes.