Each time an application is run, the first Microsoft CryptoAPI function an application calls is the CryptAcquireContext function. This function returns to the application a handle to a particular CSP. In addition, this handle specifies a particular key container within the CSP, either a specific container that you ask for, or the default for the currently logged on user. If the CSP has just been installed and no key containers yet exist, the CryptAcquireContext function can also be used to create a new one.
When an application uses CryptAcquireContext to obtain a CSP handle, it specifies a provider type and, optionally, a provider name. If both a type and a name are specified, then the function looks for a CSP with precisely the same type and name, loads it into memory, and returns a handle to the application.
When an application calls CryptAcquireContext and specifies a provider type but no provider name, the function tries to find the provider name, first on a list of default providers associated with the logged-on user and, if that fails, from a list of default providers associated with the computer.
After the provider name has been determined successfully, the CryptAcquireContext function searches for the CSP, loads it into memory, and returns a handle to the application.