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author | markm <markm@FreeBSD.org> | 2013-10-06 13:01:42 +0000 |
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committer | markm <markm@FreeBSD.org> | 2013-10-06 13:01:42 +0000 |
commit | 66c9c71f0a386308aa450979b8e7efffb171ec98 (patch) | |
tree | 167809f47614a93889070887aa95a0ac4aee264e /share/man/man4/random.4 | |
parent | eba8205cfa61df69aa2320349e9bc038fe22416f (diff) | |
download | FreeBSD-src-66c9c71f0a386308aa450979b8e7efffb171ec98.zip FreeBSD-src-66c9c71f0a386308aa450979b8e7efffb171ec98.tar.gz |
Fix up the man page for random(4). This mainly removes no-longer-relevant details about HW RNGs, reseeding explicitly and user-supplied entropy.
Diffstat (limited to 'share/man/man4/random.4')
-rw-r--r-- | share/man/man4/random.4 | 118 |
1 files changed, 53 insertions, 65 deletions
diff --git a/share/man/man4/random.4 b/share/man/man4/random.4 index 5e73bc0..4ad5b39 100644 --- a/share/man/man4/random.4 +++ b/share/man/man4/random.4 @@ -1,4 +1,4 @@ -.\" Copyright (c) 2001 Mark R V Murray. All rights reserved. +.\" Copyright (c) 2001-2013 Mark R V Murray. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions @@ -43,35 +43,48 @@ The device will probe for certain hardware entropy sources, and use these in preference to the fallback, which is a generator implemented in software. -If the kernel environment MIB's -.Va hw.nehemiah_rng_enable -or -.Va hw.ivy_rng_enable -are set to -.Dq Li 0 , -the associated hardware entropy source will be ignored. .Pp -If the device is using -the software generator, -writing data to -.Nm -would perturb the internal state. -This perturbation of the internal state -is the only userland method of introducing -extra entropy into the device. -If the writer has superuser privilege, -then closing the device after writing -will make the software generator reseed itself. -This can be used for extra security, -as it immediately introduces any/all new entropy -into the PRNG. -The hardware generators will generate -sufficient quantities of entropy, -and will therefore ignore user-supplied input. -The software +The software generator will start in an +.Em unseeded +state, and will block reads until +it is (re)seeded. +This may cause trouble at system boot +when keys and the like +are generated from +/dev/random +so steps should be taken to ensure a +reseed as soon as possible. +The +.Xr sysctl 8 +controlling the +.Em seeded +status (see below) may be used +if security is not an issue +or for convenience +during setup or development. +.Pp +This initial seeding +of random number generators +is a bootstrapping problem +that needs very careful attention. +In some cases, +it may be difficult +to find enough randomness +to seed a random number generator +until a system is fully operational, +but the system requires random numbers +to become fully operational. +It is (or more accurately should be) +critically important that the .Nm -device may be controlled with -.Xr sysctl 8 . +device is seeded +before the first time it is used. +In the case where a dummy or "blocking-only" +device is used, +it is the responsibility +of the system architect +to ensure that no blocking reads +hold up critical processes. .Pp To see the current settings of the software .Nm @@ -81,22 +94,20 @@ device, use the command line: .Pp which results in something like: .Bd -literal -offset indent -kern.random.adaptors: yarrow +kern.random.adaptors: yarrow,dummy +kern.random.active_adaptor: yarrow +kern.random.yarrow.gengateinterval: 10 +kern.random.yarrow.bins: 10 +kern.random.yarrow.fastthresh: 96 +kern.random.yarrow.slowthresh: 128 +kern.random.yarrow.slowoverthresh: 2 kern.random.sys.seeded: 1 kern.random.sys.harvest.ethernet: 1 kern.random.sys.harvest.point_to_point: 1 kern.random.sys.harvest.interrupt: 1 -kern.random.sys.harvest.swi: 0 -kern.random.yarrow.gengateinterval: 10 -kern.random.yarrow.bins: 10 -kern.random.yarrow.fastthresh: 192 -kern.random.yarrow.slowthresh: 256 -kern.random.yarrow.slowoverthresh: 2 +kern.random.sys.harvest.swi: 1 .Ed .Pp -(These would not be seen if a -hardware generator is present.) -.Pp Other than .Dl kern.random.adaptors all settings are read/write. @@ -107,9 +118,10 @@ variable indicates whether or not the .Nm device is in an acceptably secure state as a result of reseeding. -If set to 0, the device will block (on read) until the next reseed -(which can be from an explicit write, -or as a result of entropy harvesting). +If set to 0, +the device will block (on read) +until the next reseed +as a result of entropy harvesting. A reseed will set the value to 1 (non-blocking). .Pp The @@ -276,19 +288,6 @@ the generator produce independent sequences. However, the guessability or reproducibility of the sequence is unimportant, unlike the previous cases. .Pp -One final consideration for the seeding of random number generators -is a bootstrapping problem. -In some cases, it may be difficult to find enough randomness to -seed a random number generator until a system is fully operational, -but the system requires random numbers to become fully operational. -There is no substitute for careful thought here, -but the -.Fx -.Nm -device, -which is based on the Yarrow system, -should be of some help in this area. -.Pp .Fx does also provide the traditional .Xr rand 3 @@ -325,17 +324,6 @@ and is an implementation of the .Em Yarrow algorithm by Bruce Schneier, .Em et al . -The only hardware implementations -currently are for the -.Tn VIA C3 Nehemiah -(stepping 3 or greater) -CPU -and the -.Tn Intel -.Dq Bull Mountain -.Em RdRand -instruction and underlying random number generator (RNG). -More will be added in the future. .Pp The author gratefully acknowledges significant assistance from VIA Technologies, Inc. |