Cryptography and SSL/TLS Toolkit



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);

 void RAND_cleanup(void);

 /* For Win32 only */
 void RAND_screen(void);


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.


BN_rand, RAND_add, RAND_load_file, RAND_egd, RAND_bytes, RAND_set_rand_method, RAND_cleanup