.\"	$NetBSD: RAND_add.3,v 1.12 2003/07/24 14:16:42 itojun Exp $
.\"
.\" Automatically generated by Pod::Man version 1.02
.\" Thu Jul 24 13:07:59 2003
.\"
.\" Standard preamble:
.\" ======================================================================
.de Sh \" Subsection heading
.br
.if t .Sp
.ne 5
.PP
\fB\\$1\fR
.PP
..
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Ip \" List item
.br
.ie \\n(.$>=3 .ne \\$3
.el .ne 3
.IP "\\$1" \\$2
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R

.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  | will give a
.\" real vertical bar.  \*(C+ will give a nicer C++.  Capital omega is used
.\" to do unbreakable dashes and therefore won't be available.  \*(C` and
.\" \*(C' expand to `' in nroff, nothing in troff, for use with C<>
.tr \(*W-|\(bv\*(Tr
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` `
.    ds C' '
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
'br\}
.\"
.\" If the F register is turned on, we'll generate index entries on stderr
.\" for titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and
.\" index entries marked with X<> in POD.  Of course, you'll have to process
.\" the output yourself in some meaningful fashion.
.if \nF \{\
.    de IX
.    tm Index:\\$1\t\\n%\t"\\$2"
.    .
.    nr % 0
.    rr F
.\}
.\"
.\" For nroff, turn off justification.  Always turn off hyphenation; it
.\" makes way too many mistakes in technical documents.
.hy 0
.if n .na
.\"
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear.  Run.  Save yourself.  No user-serviceable parts.
.bd B 3
.    \" fudge factors for nroff and troff
.if n \{\
.    ds #H 0
.    ds #V .8m
.    ds #F .3m
.    ds #[ \f1
.    ds #] \fP
.\}
.if t \{\
.    ds #H ((1u-(\\\\n(.fu%2u))*.13m)
.    ds #V .6m
.    ds #F 0
.    ds #[ \&
.    ds #] \&
.\}
.    \" simple accents for nroff and troff
.if n \{\
.    ds ' \&
.    ds ` \&
.    ds ^ \&
.    ds , \&
.    ds ~ ~
.    ds /
.\}
.if t \{\
.    ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
.    ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
.    ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
.    ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
.    ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
.    ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.\}
.    \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
.    \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
.    \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
\{\
.    ds : e
.    ds 8 ss
.    ds o a
.    ds d- d\h'-1'\(ga
.    ds D- D\h'-1'\(hy
.    ds th \o'bp'
.    ds Th \o'LP'
.    ds ae ae
.    ds Ae AE
.\}
.rm #[ #] #H #V #F C
.\" ======================================================================
.\"
.IX Title "RAND_add 3"
.TH RAND_add 3 "0.9.7b" "2000-03-23" "OpenSSL"
.UC
.SH "NAME"
RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen \- add
entropy to the \s-1PRNG\s0
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rand.h>
.Ve
.Vb 1
\& void RAND_seed(const void *buf, int num);
.Ve
.Vb 1
\& void RAND_add(const void *buf, int num, double entropy);
.Ve
.Vb 1
\& int  RAND_status(void);
.Ve
.Vb 2
\& int  RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam);
\& void RAND_screen(void);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIRAND_add()\fR mixes the \fBnum\fR bytes at \fBbuf\fR into the \s-1PRNG\s0 state. Thus,
if the data at \fBbuf\fR are unpredictable to an adversary, this
increases the uncertainty about the state and makes the \s-1PRNG\s0 output
less predictable. Suitable input comes from user interaction (random
key presses, mouse movements) and certain hardware events. The
\&\fBentropy\fR argument is (the lower bound of) an estimate of how much
randomness is contained in \fBbuf\fR, measured in bytes. Details about
sources of randomness and how to estimate their entropy can be found
in the literature, e.g. \s-1RFC\s0 1750.
.PP
\&\fIRAND_add()\fR may be called with sensitive data such as user entered
passwords. The seed values cannot be recovered from the \s-1PRNG\s0 output.
.PP
OpenSSL makes sure that the \s-1PRNG\s0 state is unique for each thread. On
systems that provide \f(CW\*(C`/dev/urandom\*(C'\fR, the randomness device is used
to seed the \s-1PRNG\s0 transparently. However, on all other systems, the
application is responsible for seeding the \s-1PRNG\s0 by calling \fIRAND_add()\fR,
RAND_egd(3)
or RAND_load_file(3).
.PP
\&\fIRAND_seed()\fR is equivalent to \fIRAND_add()\fR when \fBnum == entropy\fR.
.PP
\&\fIRAND_event()\fR collects the entropy from Windows events such as mouse
movements and other user interaction. It should be called with the
\&\fBiMsg\fR, \fBwParam\fR and \fBlParam\fR arguments of \fIall\fR messages sent to
the window procedure. It will estimate the entropy contained in the
event message (if any), and add it to the \s-1PRNG\s0. The program can then
process the messages as usual.
.PP
The \fIRAND_screen()\fR function is available for the convenience of Windows
programmers. It adds the current contents of the screen to the \s-1PRNG\s0.
For applications that can catch Windows events, seeding the \s-1PRNG\s0 by
calling \fIRAND_event()\fR is a significantly better source of
randomness. It should be noted that both methods cannot be used on
servers that run without user interaction.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIRAND_status()\fR and \fIRAND_event()\fR return 1 if the \s-1PRNG\s0 has been seeded
with enough data, 0 otherwise.
.PP
The other functions do not return values.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
openssl_rand(3), RAND_egd(3),
RAND_load_file(3), RAND_cleanup(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIRAND_seed()\fR and \fIRAND_screen()\fR are available in all versions of SSLeay
and OpenSSL. \fIRAND_add()\fR and \fIRAND_status()\fR have been added in OpenSSL
0.9.5, \fIRAND_event()\fR in OpenSSL 0.9.5a.