.\" Copyright (c) 1997 John S. Kallal (kallal@voicenet.com)
.\"
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License, or (at your option) any later version.
.\"
.\" Some changes by tytso and aeb.
.\"
.\" 2004-12-16, John V. Belmonte/mtk, Updated init and quit scripts
.\" 2004-04-08, AEB, Improved description of read from /dev/urandom
.\" 2008-06-20, George Spelvin <linux@horizon.com>,
.\"             Matt Mackall <mpm@selenic.com>
.\"     Add a Usage subsection that recommends most users to use
.\"     /dev/urandom, and emphasizes parsimonious usage of /dev/random.
.\"
.\" Japanese Version Copyright (c) 1998
.\"           ISHIKAWA Mutsumi, all rights reserved.
.\" Translated into Japanese Mon Jan 12 03:20:27 JST 1998
.\"         by ISHIKAWA Mutsumi <ishikawa@linux.or.jp>
.\" Japanese Version Last Modified Thu Feb  5 21:08:33 JST 1998
.\"	by ISHIKAWA Mutsumi <ishikawa@linux.or.jp>
.\" Updated & Modified Sun Jun  6 14:48:03 JST 2004
.\"	by Yuichi SATO <ysato444@yahoo.co.jp>
.\" Updated & Modified Tue Jan 18 04:21:16 JST 2005 by Yuichi SATO
.\" Updated & Modified Fri Apr 22 03:44:01 JST 2005 by Yuichi SATO
.\" Updated 2008-08-13, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>, LDP v3.05
.\"
.\"WORD:	random generator	ͥ졼
.\"
.TH RANDOM 4 2008-06-20 "Linux" "Linux Programmer's Manual"
.SH ̾
random, urandom \- ͥǥХ
.SH 
(Linux 1.3.30 󶡤Ƥ) \fI/dev/random\fP 
\fI/dev/urandom\fP 饯ڥե
ͥͥ졼ؤΥ󥿥ե󶡤롣
\fI/dev/random\fP եϥ᥸㡼ǥХֹ 1
ޥʡǥХֹ 8 Ǥ롣
\fI/dev/urandom\fP ϥ᥸㡼ǥХֹ 1
ޥʡǥХֹ 9 Ǥ롣
.LP
ͥ졼ϥǥХɥ饤Ф䤽¾θδĶΥ
ȥԡסؽ롣
ޤͥ졼ϥȥԡסΥΥΥӥåȿοͤ
ݻ롣
Υȥԡס뤫롣
.LP
ɤ߹ߤԤȡ
\fI/dev/random\fP
ǥХϥȥԡסΥΥӥåȤοοͤΤ
ХȤΤߤ֤
\fI/dev/random\fP ϥ󥿥ѥå (one-time pad) 丰Τ褦
˹⤤ʼä̵ɬפˤʤӤ˸Ƥ
ȥԡס뤬λϡ\fI/dev/random\fP ɤ߽Фϡ
ʤĶΥޤǡ֥å롣
.LP
\fI/dev/urandom\fP ǥХɤ߽ФǤϡ
ȥԡ⤯ʤΤԤĤΥ֥åϹԤʤ
η̡⤷ȥԡס˽ʬʥȥԡ¸ߤʤ硢
֤ͤϤΥɥ饤ФǻȤƤ륢르ꥺ˴ŤŹ湶Фơ
Ūˤϼ夯ʤ뤳Ȥˤʤ롣
ιɤΤ褦˹ԤȤˤĤƤϡ߸ʸʤɤ
ǤϤʤΤ褦ʹŪ¸߲ǽǤ롣
⤷λۤʤ顢(\fI/dev/urandom\fP ǤϤʤ)
\fI/dev/random\fP ѤФ
.SS Ȥ
.I /dev/random

.I /dev/urandom
ΤɤȤ٤¤ä硢Ƥ
.I /dev/urandom
ȤȻפäƤϤ
̤ˡĹϤäƻȤ GPG/SSL/SSH ΥʳƤΤΤ
.I /dev/urandom
Ѥ٤Ǥ롣

ǿ侩Ƥ褦˺Ƶưե뤬¸
(Ƥμ Linux Υǥȥӥ塼ϾʤȤ 2000 ǯʹߤ
¸褦ˤʤäƤ)ư󥹤ˤ郎
ƥɤ줿ľ夫顢νϤϥΥ롼ȥǤʤ
ԤФưŹŪ˰ʤΤȤʤꡢͥåȥŹ沽Υå󥭡
ȤƻȤˤϴ˺ŬʤΤȤʤ롣
.I /dev/random
ɤ߽Ф (block) ǽΤǡ桼
Υե (non-blocking) ⡼ɤdzȤ
(⤷ϥॢȤꤷɤ߽Ф¹Ԥ)˾٥
ȥԡϤˤѤǤʤˤϡ餫ΤԤȤ

ͥͥ졼ϡŹ浿ͥ졼 (Cryptographic
pseudo-random number generator; CPRNG) μȤƻѤǤ
ʼκ򾯤뤿߷פƤ롣
®٤ǤϤʤŻ뤷߷פƤꡢ
ʥǡ̤ΤˤäŬƤʤ
桼
.I /dev/urandom
(
.IR /dev/random )
ɤ߽Фκ̤Ǥ󤹤٤Ǥ롣
ΥǥХɬפ̤Υǡɤ߽ФȡΥǥХȤ
¾Υ桼˥ޥʥαƶͿƤޤ

Ź渰Τɬפκ̤ϡμ¸ƱǤ롣
㤨С3072 ӥåȤ RSA  Diffie-Hellman ̩μ¸
128 ӥå (̩ˤˤ 2^128 ɬפȤ) Ǥꡢ
ΤḰ郎
.I /dev/random
ɤ߽Фɬפκ̤ 128 ӥå (16 Х) Ǥ롣

CPRNG 르ꥺη٤ФݸȤơκǾͤФƤ餫
ΥޡΤϤäȤѲǽʰŹץߥƥ֤
256 ӥåȤ¿ΰɬפȤ褦ʤΤϤʤ
ư٤ˡ⤷ѹʴֳ (1 ʬûʤ뤳ȤϤʤ)
٤ˡͥס뤫 256 ӥå (32 Х) ꤿɤ߽Ф
褦ʾˤϡΥץΰŹޤơ֤ʤײǽ
ȹͤ٤Ǥ
.SS 
ƥˤ餫줿 \fI/dev/random\fP 
\fI/dev/urandom\fP ¸ߤʤʤ顢Τ褦ʥޥɤǺǤ롣
.nf

    mknod \-m 644 /dev/random c 1 8
    mknod \-m 644 /dev/urandom c 1 9
    chown root:root /dev/random /dev/urandom
.fi

ڥ졼ʤ Linux ƥबưľϡ
ȥԡסϰճ˳Ѱʾ֤ˤ
ˤꡢȥԡסμºݤΥΥ̤ɾͤ꾯ʤʤ롣
θ̤Ǥäˡåȥ󤫤 () ưޤǻۤ
ȥԡסξ󤬽ˤʤ롣
ȥԡסۤˤϡ
Linux ƥεư˼¹ԤŬڤʥץȤˡ
ʲιԤɲäФ褤:
.nf

    echo "Initializing random number generator..."
    random_seed=/var/run/random-seed
    # 򺣲Υȥåפ鼡Υȥåפޤǻۤ
    # ɤԤθ塢ƤΥȥԡס¸롣
    if [ \-f $random_seed ]; then
        cat $random_seed >/dev/urandom
    else
        touch $random_seed
    fi
    chmod 600 $random_seed
    poolfile=/proc/sys/kernel/random/poolsize
    [ \-r $poolfile ] && bytes=\`cat $poolfile\` || bytes=512
    dd if=/dev/urandom of=$random_seed count=1 bs=$bytes
.fi

ޤLinux ƥΥåȥ˼¹ԤŬڤʥץȤˡ
ʲιԤɲäФ褤:
.nf

    # 򺣲Υåȥ󤫤鼡Υȥåפޤǻۤ
    # ƤΥȥԡס¸롣
    echo "Saving random seed..."
    random_seed=/var/run/random-seed
    touch $random_seed
    chmod 600 $random_seed
    poolfile=/proc/sys/kernel/random/poolsize
    [ \-r $poolfile ] && bytes=\`cat $poolfile\` || bytes=512
    dd if=/dev/urandom of=$random_seed count=1 bs=$bytes
.fi
.SS "/proc 󥿥ե"
ǥ쥯ȥ
.I /proc/sys/kernel/random
ˤե (2.3.16 ¸ߤ) ϡ
.I /dev/random
ǥХؤΤ¾Υ󥿥ե󶡤롣
.LP
ɤ߹ѤΥե
.I entropy_avail
ϻѲǽʥȥԡɽ
̾ 4096 (ӥå) ˤʤꡢȥԡס뤬դξ֤Ǥ롣
.LP
ե
.I poolsize
ϥȥԡסΥɽ
Υեΰ̣ϥͥСˤۤʤ롣
.RS
.TP 12
Linux 2.4:
ΥեϥȥԡסΥ֥Хȡñ̤ǵꤹ롣
̾Υեͤ 512 ˤʤ뤬񤭹߲ǽǤꡢ
르ꥺѲǽǤդͤѹǤ롣
ǽͤ 32, 64, 128, 256, 512, 1024, 2048 Ǥ롣
.TP
Linux 2.6:
Υեɤ߽ФѤǤꡢ
ȥԡסΥ֥ӥåȡñ̤ǵꤹ롣
ͤ 4096 Ǥ롣
.RE
.LP
ե
.I read_wakeup_threshold

.I /dev/random
ΥȥԡԤäƵٻߤƤץ򵯤Τɬפ
ȥԡΥӥåȿݻƤ롣
ǥեȤ 64 Ǥ롣
ե
.I write_wakeup_threshold
ϥȥԡΥӥåȿݻƤꡢͰʲˤʤä
.I /dev/random
ؤν񤭹ߥΤ
.BR select (2)
ޤ
.BR poll (2)
¹Ԥץ򵯤
ͤϥե˽񤭹ߤԤȤˤäѹǤ롣
.LP
ɤ߹ѤΥե
.I uuid

.I boot_id
 6fd5a44b-35f4-4ad4-a9b9-6b9be13e1fe9 Τ褦
ʸݻƤ롣
Ԥɤ߹ߤ٤˿졢
Ԥ 1 ٤롣
.SH ե
/dev/random
.br
/dev/urandom
.\" .SH 
.\" ͥ롦ʥСͥ졼 Theodora Ts'o
.\" (tytso@athena.mit.edu) ˤäƽ񤫤줿
.SH Ϣ
mknod (1)
.br
RFC\ 1750, "Randomness Recommendations for Security"
.\" .SH 
.\"   <ishikawa@linux.or.jp>