The CRYPT_KEY_PROV_PARAM structure fields are passed as the arguments to CryptSetProvParam. This structure is pointed to by the rgProvParam in the CRYPT_KEY_PROV_INFO data structure.
typedef struct _CRYPT_KEY_PROV_PARAM {
    DWORD           dwParam;
    BYTE*           pbData;
    DWORD           cbData;
    DWORD           dwFlags;
} CRYPT_KEY_PROV_PARAM, *PCRYPT_KEY_PROV_PARAM;