CSP Architectural Overview

Applications do not communicate directly with a CSP. Instead, applications call CryptoAPI functions exposed by the operating system's Advapi32.dll and Crypt32.dll files. The operating system filters these function calls and passes them on to the appropriate CSP functions through CryptoSPI (a system program interface).

The CSP writer must know the nature, order, and meaning of parameters passed by the operating system to the CSP functions and must return the values as expected to the operating system.

Applications use handles to refer to data objects within the CSP. Objects that are referenced by their handles include key containers, hash objects, session key objects, and public/private key pair objects. These handles are opaque from both sides; that is, the handle that the application uses to access a data object is not the same one that the CSP uses. For various reasons, the operating system layer always accesses data objects indirectly using handles.