RAND_add(3) OpenSSL RAND_add(3) NNAAMMEE RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen - add entropy to the PRNG SSYYNNOOPPSSIISS #include void RAND_seed(const void *buf, int num); void RAND_add(const void *buf, int num, double entropy); int RAND_status(void); int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam); void RAND_screen(void); DDEESSCCRRIIPPTTIIOONN _R_A_N_D___a_d_d_(_) mixes the nnuumm bytes at bbuuff into the PRNG state. Thus, if the data at bbuuff 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 eennttrrooppyy argument is (the lower bound of) an estimate of how much randomness is contained in bbuuff, measured in bytes. Details about sources of randomness and how to esti- mate their entropy can be found in the literature, e.g. RFC 1750. _R_A_N_D___a_d_d_(_) may be called with sensitive data such as user entered pass- words. The seed values cannot be recovered from the PRNG output. OpenSSL makes sure that the PRNG state is unique for each thread. On systems that provide "/dev/urandom", the randomness device is used to seed the PRNG transparently. However, on all other systems, the appli- cation is responsible for seeding the PRNG by calling _R_A_N_D___a_d_d_(_), _R_A_N_D___e_g_d(3) or _R_A_N_D___l_o_a_d___f_i_l_e(3). _R_A_N_D___s_e_e_d_(_) is equivalent to _R_A_N_D___a_d_d_(_) when nnuumm ==== eennttrrooppyy. _R_A_N_D___e_v_e_n_t_(_) collects the entropy from Windows events such as mouse movements and other user interaction. It should be called with the iiMMssgg, wwPPaarraamm and llPPaarraamm arguments of _a_l_l messages sent to the window procedure. It will estimate the entropy contained in the event message (if any), and add it to the PRNG. The program can then process the mes- sages as usual. The _R_A_N_D___s_c_r_e_e_n_(_) function is available for the convenience of Windows programmers. It adds the current contents of the screen to the PRNG. For applications that can catch Windows events, seeding the PRNG by calling _R_A_N_D___e_v_e_n_t_(_) is a significantly better source of randomness. It should be noted that both methods cannot be used on servers that run without user interaction. RREETTUURRNN VVAALLUUEESS _R_A_N_D___s_t_a_t_u_s_(_) and _R_A_N_D___e_v_e_n_t_(_) return 1 if the PRNG has been seeded with enough data, 0 otherwise. The other functions do not return values. SSEEEE AALLSSOO _r_a_n_d(3), _R_A_N_D___e_g_d(3), _R_A_N_D___l_o_a_d___f_i_l_e(3), _R_A_N_D___c_l_e_a_n_u_p(3) HHIISSTTOORRYY _R_A_N_D___s_e_e_d_(_) and _R_A_N_D___s_c_r_e_e_n_(_) are available in all versions of SSLeay and OpenSSL. _R_A_N_D___a_d_d_(_) and _R_A_N_D___s_t_a_t_u_s_(_) have been added in OpenSSL 0.9.5, _R_A_N_D___e_v_e_n_t_(_) in OpenSSL 0.9.5a. 1.0.1u 2016-09-22 RAND_add(3)