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[dragonfly.git] / secure / lib / libcrypto / man / RAND_add.3
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80.\" If the F register is turned on, we'll generate
81.\" index entries out stderr for the following things:
82.\" TH Title
83.\" SH Header
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96.TH RAND_add 3 "0.9.7d" "2/Sep/2004" "OpenSSL"
97.UC
98.if n .hy 0
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188.\}
189.rm #[ #] #H #V #F C
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190.SH "NAME"
191RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen \- add
74dab6c2 192entropy to the PRNG
984263bc 193.SH "SYNOPSIS"
74dab6c2 194.PP
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195.Vb 1
196\& #include <openssl/rand.h>
197.Ve
198.Vb 1
199\& void RAND_seed(const void *buf, int num);
200.Ve
201.Vb 1
202\& void RAND_add(const void *buf, int num, double entropy);
203.Ve
204.Vb 1
205\& int RAND_status(void);
206.Ve
207.Vb 2
208\& int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
209\& void RAND_screen(void);
210.Ve
211.SH "DESCRIPTION"
74dab6c2 212\fIRAND_add()\fR mixes the \fBnum\fR bytes at \fBbuf\fR into the PRNG state. Thus,
984263bc 213if the data at \fBbuf\fR are unpredictable to an adversary, this
74dab6c2 214increases the uncertainty about the state and makes the PRNG output
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215less predictable. Suitable input comes from user interaction (random
216key presses, mouse movements) and certain hardware events. The
74dab6c2 217\fBentropy\fR argument is (the lower bound of) an estimate of how much
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218randomness is contained in \fBbuf\fR, measured in bytes. Details about
219sources of randomness and how to estimate their entropy can be found
74dab6c2 220in the literature, e.g. RFC 1750.
984263bc 221.PP
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222\fIRAND_add()\fR may be called with sensitive data such as user entered
223passwords. The seed values cannot be recovered from the PRNG output.
984263bc 224.PP
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225OpenSSL makes sure that the PRNG state is unique for each thread. On
226systems that provide \f(CW/dev/urandom\fR, the randomness device is used
227to seed the PRNG transparently. However, on all other systems, the
228application is responsible for seeding the PRNG by calling \fIRAND_add()\fR,
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229RAND_egd(3)
230or RAND_load_file(3).
231.PP
74dab6c2 232\fIRAND_seed()\fR is equivalent to \fIRAND_add()\fR when \fBnum == entropy\fR.
984263bc 233.PP
74dab6c2 234\fIRAND_event()\fR collects the entropy from Windows events such as mouse
984263bc 235movements and other user interaction. It should be called with the
74dab6c2 236\fBiMsg\fR, \fBwParam\fR and \fBlParam\fR arguments of \fIall\fR messages sent to
984263bc 237the window procedure. It will estimate the entropy contained in the
74dab6c2 238event message (if any), and add it to the PRNG. The program can then
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239process the messages as usual.
240.PP
241The \fIRAND_screen()\fR function is available for the convenience of Windows
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242programmers. It adds the current contents of the screen to the PRNG.
243For applications that can catch Windows events, seeding the PRNG by
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244calling \fIRAND_event()\fR is a significantly better source of
245randomness. It should be noted that both methods cannot be used on
246servers that run without user interaction.
247.SH "RETURN VALUES"
74dab6c2 248\fIRAND_status()\fR and \fIRAND_event()\fR return 1 if the PRNG has been seeded
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249with enough data, 0 otherwise.
250.PP
251The other functions do not return values.
252.SH "SEE ALSO"
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253rand(3), RAND_egd(3),
254RAND_load_file(3), RAND_cleanup(3)
255.SH "HISTORY"
74dab6c2 256\fIRAND_seed()\fR and \fIRAND_screen()\fR are available in all versions of SSLeay
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257and OpenSSL. \fIRAND_add()\fR and \fIRAND_status()\fR have been added in OpenSSL
2580.9.5, \fIRAND_event()\fR in OpenSSL 0.9.5a.
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259
260.rn }` ''
261.IX Title "RAND_add 3"
262.IX Name "RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen - add
263entropy to the PRNG"
264
265.IX Header "NAME"
266
267.IX Header "SYNOPSIS"
268
269.IX Header "DESCRIPTION"
270
271.IX Header "RETURN VALUES"
272
273.IX Header "SEE ALSO"
274
275.IX Header "HISTORY"
276