rand - pseudo-random number generator
#include <openssl/rand.h> int RAND_set_rand_engine(ENGINE *engine); int RAND_bytes(unsigned char *buf, int num); int RAND_pseudo_bytes(unsigned char *buf, int num); void RAND_seed(const void *buf, int num); void RAND_add(const void *buf, int num, int entropy); int RAND_status(void); int RAND_load_file(const char *file, long max_bytes); int RAND_write_file(const char *file); const char *RAND_file_name(char *file, size_t num); int RAND_egd(const char *path); void RAND_set_rand_method(const RAND_METHOD *meth); const RAND_METHOD *RAND_get_rand_method(void); RAND_METHOD *RAND_OpenSSL(void); void RAND_cleanup(void); /* For Win32 only */ void RAND_screen(void); int RAND_event(UINT, WPARAM, LPARAM);
Since the introduction of the ENGINE API, the recommended way of controlling default implementations is by using the ENGINE API functions. The default RAND_METHOD, as set by RAND_set_rand_method() and returned by RAND_get_rand_method(), is only used if no ENGINE has been set as the default "rand" implementation. Hence, these two functions are no longer the recommended way to control defaults.
If an alternative RAND_METHOD implementation is being used (either set directly or as provided by an ENGINE module), then it is entirely responsible for the generation and management of a cryptographically secure PRNG stream. The mechanisms described below relate solely to the software PRNG implementation built in to OpenSSL and used by default.
These functions implement a cryptographically secure pseudo-random number generator (PRNG). It is used by other library functions for example to generate random keys, and applications can use it when they need randomness.
A cryptographic PRNG must be seeded with unpredictable data such as mouse movements or keys pressed at random by the user. This is described in RAND_add. Its state can be saved in a seed file (see RAND_load_file) to avoid having to go through the seeding process whenever the application is started.
RAND_bytes describes how to obtain random data from the PRNG.