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131 .IX Title "RAND_add 3"
132 .TH RAND_add 3 "2005-02-24" "0.9.7d" "OpenSSL"
134 RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen \- add
137 .IX Header "SYNOPSIS"
139 \& #include <openssl/rand.h>
143 \& void RAND_seed(const void *buf, int num);
147 \& void RAND_add(const void *buf, int num, double entropy);
151 \& int RAND_status(void);
155 \& int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
156 \& void RAND_screen(void);
159 .IX Header "DESCRIPTION"
160 \&\fIRAND_add()\fR mixes the \fBnum\fR bytes at \fBbuf\fR into the \s-1PRNG\s0 state. Thus,
161 if the data at \fBbuf\fR are unpredictable to an adversary, this
162 increases the uncertainty about the state and makes the \s-1PRNG\s0 output
163 less predictable. Suitable input comes from user interaction (random
164 key presses, mouse movements) and certain hardware events. The
165 \&\fBentropy\fR argument is (the lower bound of) an estimate of how much
166 randomness is contained in \fBbuf\fR, measured in bytes. Details about
167 sources of randomness and how to estimate their entropy can be found
168 in the literature, e.g. \s-1RFC\s0 1750.
170 \&\fIRAND_add()\fR may be called with sensitive data such as user entered
171 passwords. The seed values cannot be recovered from the \s-1PRNG\s0 output.
173 OpenSSL makes sure that the \s-1PRNG\s0 state is unique for each thread. On
174 systems that provide \f(CW\*(C`/dev/urandom\*(C'\fR, the randomness device is used
175 to seed the \s-1PRNG\s0 transparently. However, on all other systems, the
176 application is responsible for seeding the \s-1PRNG\s0 by calling \fIRAND_add()\fR,
177 \&\fIRAND_egd\fR\|(3)
178 or \fIRAND_load_file\fR\|(3).
180 \&\fIRAND_seed()\fR is equivalent to \fIRAND_add()\fR when \fBnum == entropy\fR.
182 \&\fIRAND_event()\fR collects the entropy from Windows events such as mouse
183 movements and other user interaction. It should be called with the
184 \&\fBiMsg\fR, \fBwParam\fR and \fBlParam\fR arguments of \fIall\fR messages sent to
185 the window procedure. It will estimate the entropy contained in the
186 event message (if any), and add it to the \s-1PRNG\s0. The program can then
187 process the messages as usual.
189 The \fIRAND_screen()\fR function is available for the convenience of Windows
190 programmers. It adds the current contents of the screen to the \s-1PRNG\s0.
191 For applications that can catch Windows events, seeding the \s-1PRNG\s0 by
192 calling \fIRAND_event()\fR is a significantly better source of
193 randomness. It should be noted that both methods cannot be used on
194 servers that run without user interaction.
196 .IX Header "RETURN VALUES"
197 \&\fIRAND_status()\fR and \fIRAND_event()\fR return 1 if the \s-1PRNG\s0 has been seeded
198 with enough data, 0 otherwise.
200 The other functions do not return values.
202 .IX Header "SEE ALSO"
203 \&\fIrand\fR\|(3), \fIRAND_egd\fR\|(3),
204 \&\fIRAND_load_file\fR\|(3), \fIRAND_cleanup\fR\|(3)
207 \&\fIRAND_seed()\fR and \fIRAND_screen()\fR are available in all versions of SSLeay
208 and OpenSSL. \fIRAND_add()\fR and \fIRAND_status()\fR have been added in OpenSSL
209 0.9.5, \fIRAND_event()\fR in OpenSSL 0.9.5a.