Cryptography and SSL/TLS Toolkit



RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen - add randomness to the PRNG


 #include <openssl/rand.h>

 void RAND_seed(const void *buf, int num);

 void RAND_add(const void *buf, int num, double randomness);

 int  RAND_status(void);

 #if OPENSSL_API_COMPAT < 0x10100000L
 int  RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
 void RAND_screen(void);


RAND_add() mixes the num bytes at buf into the PRNG state. Thus, if the data at buf are unpredictable to an adversary, this increases the uncertainty about the state and makes the PRNG output less predictable. Suitable input comes from user interaction (random key presses, mouse movements) and certain hardware events. The randomness argument is an estimate of how much randomness is contained in buf, in bytes, and should be a number between zero and num. Details about sources of randomness and how to estimate their randomness can be found in the literature; for example IETF RFC 4086.

RAND_add() may be called with sensitive data such as user entered passwords. The seed values cannot be recovered from the PRNG output.

RAND_seed() is equivalent to RAND_add() with randomness set to num.

On systems that provide /dev/urandom or similar source of randomess, it will be used to seed the PRNG transparently. On older systems, however, it might be necessary to use RAND_add(), RAND_egd(3) or RAND_load_file(3).

RAND_event() and RAND_screen() are deprecated and should not be called.


RAND_status() returns 1 if the PRNG has been seeded with enough data, 0 otherwise.

RAND_event() calls RAND_poll() and returns RAND_status().

RAND_screen calls RAND_poll().

The other functions do not return values.


RAND_event() and RAND_screen() are deprecated since OpenSSL 1.1.0. Use the functions described above instead.


RAND_bytes(3), RAND_egd(3), RAND_load_file(3)

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