Security Support Provider Interface (SSPI) is a component of

Windows API The Windows API, informally WinAPI, is the foundational application programming interface (API) that allows a computer program to access the features of the Microsoft Windows operating system in which the program is running. Programs can acces ...

that performs security-related operations such as

authentication Authentication (from ''authentikos'', "real, genuine", from αὐθέντης ''authentes'', "author") is the act of proving an Logical assertion, assertion, such as the Digital identity, identity of a computer system user. In contrast with iden ...

. SSPI functions as a common interface to several Security Support Providers (SSPs): A Security Support Provider is a

dynamic-link library A dynamic-link library (DLL) is a shared library in the Microsoft Windows or OS/2 operating system. A DLL can contain executable code (functions), data, and resources. A DLL file often has file extension .dll even though this is not required ...

(DLL) that makes one or more security packages available to apps.

Providers

The following SSPs are included in Windows: * NTLMSSP (msv1_0.dll) – Introduced in Windows NT 3.51. Provides

NTLM In a Windows network, NT (New Technology) LAN Manager (NTLM) is a suite of Microsoft security protocols intended to provide authentication, integrity, and confidentiality to users. NTLM is the successor to the authentication protocol in Microsoft ...

challenge/response authentication for Windows domains prior to

Windows 2000 Windows 2000 is a major release of the Windows NT operating system developed by Microsoft, targeting the server and business markets. It is the direct successor to Windows NT 4.0, and was Software release life cycle#Release to manufacturing (RT ...

and for systems that are not part of a domain. * Kerberos (kerberos.dll) – Introduced in

and updated in

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...

to support AES. Performs authentication for Windows domains in Windows 2000 and later. * NegotiateSSP (secur32.dll) – Introduced in Windows 2000. Provides single sign-on capability, sometimes referred to as Integrated Windows Authentication (especially in the context of IIS). Prior to

Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on July 22, 2009, and became generally available on October 22, ...

, it tries Kerberos before falling back to NTLM. On Windows 7 and later, NEGOExts is introduced, which negotiates the use of installed custom SSPs which are supported on the client and server for authentication. * Secure Channel (schannel.dll) – Introduced in Windows 2000 and updated in Windows Vista to support stronger AES encryption and ECC This provider uses SSL/TLS records to encrypt data payloads. * TLS/SSL –

Public key cryptography Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic al ...

SSP that provides encryption and secure communication for authenticating clients and servers over the internet. Updated in Windows 7 to support TLS 1.2. * Digest SSP (wdigest.dll) – Introduced in

Windows XP Windows XP is a major release of Microsoft's Windows NT operating system. It was released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct successor to Windows 2000 for high-end and business users a ...

. Provides challenge/response based HTTP and SASL authentication between Windows and non-Windows systems where Kerberos is not available. * CredSSP (credssp.dll) – Introduced in

and available on Windows XP SP3. Provides single sign-on and Network Level Authentication for Remote Desktop Services. * Distributed Password Authentication (DPA, msapsspc.dll) – Introduced in Windows 2000. Provides internet authentication using digital certificates. * Public Key Cryptography User-to-User (PKU2U, pku2u.dll) – Introduced in

. Provides peer-to-peer authentication using digital certificates between systems that are not part of a domain.

Comparison

SSPI is a proprietary variant of Generic Security Services Application Program Interface (GSSAPI) with extensions and very Windows-specific data types. It shipped with Windows NT 3.51 and

Windows 95 Windows 95 is a consumer-oriented operating system developed by Microsoft and the first of its Windows 9x family of operating systems, released to manufacturing on July 14, 1995, and generally to retail on August 24, 1995. Windows 95 merged ...

with the NTLMSSP. For Windows 2000, an implementation of Kerberos 5 was added, using token formats conforming to the official protocol standard RFC 1964 (The Kerberos 5 GSSAPI mechanism) and providing wire-level interoperability with Kerberos 5 implementations from other vendors. The tokens generated and accepted by the SSPI are mostly compatible with the GSS-API so an SSPI client on Windows may be able to authenticate with a GSS-API server on Unix depending on the specific circumstances. One significant shortcoming of SSPI is its lack of

channel binding In cryptography, the Salted Challenge Response Authentication Mechanism (SCRAM) is a family of modern, password-based challenge–response authentication mechanisms providing authentication of a user to a server. As it is specified for Simple Aut ...

s, which makes some GSSAPI interoperability impossible. Another fundamental difference between the

IETF The Internet Engineering Task Force (IETF) is a standards organization for the Internet standard, Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster ...

-defined GSSAPI and Microsoft's SSPI is the concept of " impersonation". In this model, a server can operate with the ''full'' privileges of the authenticated client, so that the operating system performs all

access control In physical security and information security, access control (AC) is the action of deciding whether a subject should be granted or denied access to an object (for example, a place or a resource). The act of ''accessing'' may mean consuming ...

checks, e.g. when opening new files. Whether these are less privileges or more privileges than that of the original service account depends entirely on the client. In the traditional (GSSAPI) model, when a server runs under a service account, it cannot elevate its privileges, and has to perform access control in a client-specific and application-specific fashion. The obvious negative security implications of the impersonation concept are prevented in Windows Vista by restricting impersonation to selected service accounts. Impersonation can be implemented in a Unix/Linux model using the seteuid or related system calls. While this means an unprivileged process cannot elevate its privileges, it also means that to take advantage of impersonation the process must run in the context of the root user account.

References

External links

SSPI Reference on MSDN

Example of use of SSPI for HTTP authentification
{{SSL/TLS Microsoft application programming interfaces Microsoft Windows security technology Transport Layer Security implementation