201 lines
6.7 KiB
Groff
201 lines
6.7 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "RAND_add 3"
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.TH RAND_add 3 "2014-10-15" "1.0.1j" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen \- add
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entropy to the PRNG
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/rand.h>
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\&
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\& void RAND_seed(const void *buf, int num);
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\&
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\& void RAND_add(const void *buf, int num, double entropy);
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\&
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\& int RAND_status(void);
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\&
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\& int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
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\& void RAND_screen(void);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIRAND_add()\fR mixes the \fBnum\fR bytes at \fBbuf\fR into the \s-1PRNG\s0 state. Thus,
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if the data at \fBbuf\fR are unpredictable to an adversary, this
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increases the uncertainty about the state and makes the \s-1PRNG\s0 output
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less predictable. Suitable input comes from user interaction (random
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key presses, mouse movements) and certain hardware events. The
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\&\fBentropy\fR argument is (the lower bound of) an estimate of how much
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randomness is contained in \fBbuf\fR, measured in bytes. Details about
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sources of randomness and how to estimate their entropy can be found
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in the literature, e.g. \s-1RFC\s0 1750.
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.PP
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\&\fIRAND_add()\fR may be called with sensitive data such as user entered
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passwords. The seed values cannot be recovered from the \s-1PRNG\s0 output.
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.PP
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OpenSSL makes sure that the \s-1PRNG\s0 state is unique for each thread. On
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systems that provide \f(CW\*(C`/dev/urandom\*(C'\fR, the randomness device is used
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to seed the \s-1PRNG\s0 transparently. However, on all other systems, the
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application is responsible for seeding the \s-1PRNG\s0 by calling \fIRAND_add()\fR,
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\&\fIRAND_egd\fR\|(3)
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or \fIRAND_load_file\fR\|(3).
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.PP
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\&\fIRAND_seed()\fR is equivalent to \fIRAND_add()\fR when \fBnum == entropy\fR.
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.PP
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\&\fIRAND_event()\fR collects the entropy from Windows events such as mouse
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movements and other user interaction. It should be called with the
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\&\fBiMsg\fR, \fBwParam\fR and \fBlParam\fR arguments of \fIall\fR messages sent to
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the window procedure. It will estimate the entropy contained in the
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event message (if any), and add it to the \s-1PRNG\s0. The program can then
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process the messages as usual.
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.PP
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The \fIRAND_screen()\fR function is available for the convenience of Windows
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programmers. It adds the current contents of the screen to the \s-1PRNG\s0.
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For applications that can catch Windows events, seeding the \s-1PRNG\s0 by
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calling \fIRAND_event()\fR is a significantly better source of
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randomness. It should be noted that both methods cannot be used on
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servers that run without user interaction.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIRAND_status()\fR and \fIRAND_event()\fR return 1 if the \s-1PRNG\s0 has been seeded
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with enough data, 0 otherwise.
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.PP
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The other functions do not return values.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIrand\fR\|(3), \fIRAND_egd\fR\|(3),
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\&\fIRAND_load_file\fR\|(3), \fIRAND_cleanup\fR\|(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIRAND_seed()\fR and \fIRAND_screen()\fR are available in all versions of SSLeay
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and OpenSSL. \fIRAND_add()\fR and \fIRAND_status()\fR have been added in OpenSSL
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0.9.5, \fIRAND_event()\fR in OpenSSL 0.9.5a.
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