CredSSP provides an encrypted Transport Layer Security Protocol channel.
The client is authenticated over the encrypted channel by using the Simple and Protected GSSAPI Negotiation Mechanism (SPNEGO) protocol with either Microsoft Kerberos or Microsoft NTLM.
After the client and server are authenticated, the client passes the user's credentials to the server. The credentials are doubly encrypted under the SPNEGO and TLS session keys.
CredSSP supports Password-based logon as well as Smart Card logon based on both X.509 and PKINIT.
There might be more information for this subject on one of the following: