Client and server applications enable application protocol negotiation extension by supplying lists of supported application protocol IDs, in descending order of preference. When the TLS client makes the request to the server, the TLS server reads its supported protocol list for the most-preferred application protocol which the client also supports. If such a protocol is found, the server responds with the selected protocol ID and continues with the handshake as usual.
If there is no common application protocol, the server sends a fatal handshake failure alert. When authentication of the client computer is required using SSL or TLS, the server can be configured to send a list of trusted certificate issuers. This list contains the set of certificate issuers which the server will trust and is a hint to the client computer as to which client certificate to select if there are multiple certificates present.
In addition, the certificate chain the client computer sends to the server must be validated against the configured trusted issuers list. In Windows Server and Windows 8, changes were made to the underlying authentication process so that:. The behavior to send the Trusted Issuer List by default is off: Default value of the SendTrustedIssuerList registry key is now 0 off by default instead of 1.
Beginning with Windows Server , the use of the CTL has been replaced with a certificate store-based implementation. This allows for more familiar manageability through the existing certificate management commandlets of the PowerShell provider, as well as command line tools such as certutil.
Although the maximum size of the trusted certification authorities list that the Schannel SSP supports 16 KB remains the same as in Windows Server R2 , in Windows Server there is a new dedicated certificate store for client authentication issuers so that unrelated certificates are not included in the message. In Windows Server , the trusted issuers list is configured using certificate stores; one default global computer certificate store and one that is optional per site.
The source of the list will be determined as follows:. If no certificates exist in the application-defined store, then Schannel checks the Client Authentication Issuers store on the local computer and, if certificates are present, uses that store as the source. If no certificate is found in either store, the Trusted Roots store is checked. If neither the global or local stores contain certificates, the Schannel provider will use the Trusted Root Certifictation Authorities store as the source of trusted issuers list.
This is the behavior for Windows Server R2. If the Trusted Root Certifictation Authorities store that was used contains a mix of Root self-signed and certification authority CA Issuer certificates, only the CA Issuer certificates will be sent to the server by default.
When two computers or devices need to be authenticated so that they can communicate securely, the requests for authentication are routed to the SSPI, which completes the authentication process, regardless of the network protocol currently in use.
The SSPI returns transparent binary large objects. These are passed between the applications, at which point they can be passed to the SSPI layer. Thus, the SSPI enables an application to use various security models available on a computer or network without changing the interface to the security system.
The SSPs are used in different ways in Windows operating systems to promote secure communication in an unsecure network environment. Negotiate Extensions Security Support Provider. Security Support Provider selection. It is an industry standard protocol that is used with a password or a smart card for an interactive logon. It is also the preferred authentication method for services in Windows. Because the Kerberos protocol has been the default authentication protocol since Windows , all domain services support the Kerberos SSP.
These services include:. This provider is included by default in versions designated in the Applies to list at the beginning of this topic, plus Windows Server and Windows XP. Microsoft Kerberos Windows. Kerberos Enhancements for Windows Vista. Changes in Kerberos Authentication for Windows 7. Kerberos Authentication Technical Reference. Auditing and restricting NTLM usage guide.
Digest authentication transmits credentials across the network as an MD5 hash or message digest. Microsoft Digest Authentication Windows. The Secure Channel Schannel is used for web-based server authentication, such as when a user attempts to access a secure web server. Schannel provides all these protocols. The Schannel SSP uses public key certificates to authenticate parties. When authenticating parties, Schannel SSP selects a protocol in the following order of preference:.
The protocol that is selected is the preferred authentication protocol that the client and the server can support. For example, if a server supports all the Schannel protocols and the client supports only SSL 3. DTLS is used when explicitly called by the application. TLS 1. Secure Channel Windows. Some of the work I've been doing for my company for the last couple of years has had me using libcurl. I recently received permission to contribute libcurl work back to the open source community.
Comparing what I implemented to what Marc has done, I think his implementation is very good and should go forward. I may have a few small improvements to offer though so I will probably follow with some patches headed either his way or to the libcurl community.
I called my implementation "winssl.
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