Update build for OpenSSL-0.9.8j upgrade.
[dragonfly.git] / secure / lib / libcrypto / man / RAND_add.3
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132.\" ========================================================================
133.\"
134.IX Title "RAND_add 3"
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135.TH RAND_add 3 "2009-01-11" "0.9.8j" "OpenSSL"
136.\" For nroff, turn off justification. Always turn off hyphenation; it makes
137.\" way too many mistakes in technical documents.
138.if n .ad l
139.nh
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140.SH "NAME"
141RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen \- add
74dab6c2 142entropy to the PRNG
984263bc 143.SH "SYNOPSIS"
8b0cefbb 144.IX Header "SYNOPSIS"
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145.Vb 1
146\& #include <openssl/rand.h>
e257b235 147\&
984263bc 148\& void RAND_seed(const void *buf, int num);
e257b235 149\&
984263bc 150\& void RAND_add(const void *buf, int num, double entropy);
e257b235 151\&
984263bc 152\& int RAND_status(void);
e257b235 153\&
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154\& int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
155\& void RAND_screen(void);
156.Ve
157.SH "DESCRIPTION"
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158.IX Header "DESCRIPTION"
159\&\fIRAND_add()\fR mixes the \fBnum\fR bytes at \fBbuf\fR into the \s-1PRNG\s0 state. Thus,
984263bc 160if the data at \fBbuf\fR are unpredictable to an adversary, this
8b0cefbb 161increases the uncertainty about the state and makes the \s-1PRNG\s0 output
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162less predictable. Suitable input comes from user interaction (random
163key presses, mouse movements) and certain hardware events. The
8b0cefbb 164\&\fBentropy\fR argument is (the lower bound of) an estimate of how much
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165randomness is contained in \fBbuf\fR, measured in bytes. Details about
166sources of randomness and how to estimate their entropy can be found
8b0cefbb 167in the literature, e.g. \s-1RFC\s0 1750.
984263bc 168.PP
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169\&\fIRAND_add()\fR may be called with sensitive data such as user entered
170passwords. The seed values cannot be recovered from the \s-1PRNG\s0 output.
984263bc 171.PP
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172OpenSSL makes sure that the \s-1PRNG\s0 state is unique for each thread. On
173systems that provide \f(CW\*(C`/dev/urandom\*(C'\fR, the randomness device is used
174to seed the \s-1PRNG\s0 transparently. However, on all other systems, the
175application is responsible for seeding the \s-1PRNG\s0 by calling \fIRAND_add()\fR,
176\&\fIRAND_egd\fR\|(3)
177or \fIRAND_load_file\fR\|(3).
984263bc 178.PP
8b0cefbb 179\&\fIRAND_seed()\fR is equivalent to \fIRAND_add()\fR when \fBnum == entropy\fR.
984263bc 180.PP
8b0cefbb 181\&\fIRAND_event()\fR collects the entropy from Windows events such as mouse
984263bc 182movements and other user interaction. It should be called with the
8b0cefbb 183\&\fBiMsg\fR, \fBwParam\fR and \fBlParam\fR arguments of \fIall\fR messages sent to
984263bc 184the window procedure. It will estimate the entropy contained in the
8b0cefbb 185event message (if any), and add it to the \s-1PRNG\s0. The program can then
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186process the messages as usual.
187.PP
188The \fIRAND_screen()\fR function is available for the convenience of Windows
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189programmers. It adds the current contents of the screen to the \s-1PRNG\s0.
190For applications that can catch Windows events, seeding the \s-1PRNG\s0 by
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191calling \fIRAND_event()\fR is a significantly better source of
192randomness. It should be noted that both methods cannot be used on
193servers that run without user interaction.
194.SH "RETURN VALUES"
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195.IX Header "RETURN VALUES"
196\&\fIRAND_status()\fR and \fIRAND_event()\fR return 1 if the \s-1PRNG\s0 has been seeded
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197with enough data, 0 otherwise.
198.PP
199The other functions do not return values.
200.SH "SEE ALSO"
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201.IX Header "SEE ALSO"
202\&\fIrand\fR\|(3), \fIRAND_egd\fR\|(3),
203\&\fIRAND_load_file\fR\|(3), \fIRAND_cleanup\fR\|(3)
984263bc 204.SH "HISTORY"
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205.IX Header "HISTORY"
206\&\fIRAND_seed()\fR and \fIRAND_screen()\fR are available in all versions of SSLeay
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207and OpenSSL. \fIRAND_add()\fR and \fIRAND_status()\fR have been added in OpenSSL
2080.9.5, \fIRAND_event()\fR in OpenSSL 0.9.5a.