- (dtucker) [openbsd-compat/openbsd-compat.h] Fix prototypes, spotted by

[openssh.git] / WARNING.RNG

diff --git a/WARNING.RNG b/WARNING.RNG
index 5f129f402bdc5febdbf019678ec13d9898484d20..d876c887c8465e0b6cc590b0aa74fcd6b848618e 100644 (file)
--- a/WARNING.RNG
+++ b/WARNING.RNG
@@ -12,24 +12,28 @@ A particularly pernicious problem arises with DSA keys (used by the
 ssh2 protocol). Performing a DSA signature (which is required for
 authentication), entails the use of a 160 bit random number.  If an
 attacker can predict this number, then they can deduce your *private*
 ssh2 protocol). Performing a DSA signature (which is required for
 authentication), entails the use of a 160 bit random number.  If an
 attacker can predict this number, then they can deduce your *private*

-key and impersonate you.
+key and impersonate you or your hosts.

 
 If you are using the builtin random number support (configure will
 
 If you are using the builtin random number support (configure will

-tell you if this is the case), then read this document in its entirety
-and consider disabling ssh2 support (by adding "Protocol 1" to
-sshd_config and ssh_config).
+tell you if this is the case), then read this document in its entirety.
+Alternately, you can use Lutz Jaenicke's PRNGd - a small daemon which
+collects random numbers and makes them available by a socket.

 
 Please also request that your OS vendor provides a kernel-based random
 number collector (/dev/random) in future versions of your operating
 
 Please also request that your OS vendor provides a kernel-based random
 number collector (/dev/random) in future versions of your operating

-systems.
+systems by default.

 
 On to the description...
 
 The portable OpenSSH contains random number collection support for
 systems which lack a kernel entropy pool (/dev/random).
 
 
 On to the description...
 
 The portable OpenSSH contains random number collection support for
 systems which lack a kernel entropy pool (/dev/random).
 

-This collector operates by executing the programs listed in
-($etcdir)/ssh_prng_cmds, reading their output and adding it to the
+This collector (as of 3.1 and beyond) comes as an external application
+that allows the local admin to decide on how to implement entropy
+collection.
+
+The default entropy collector operates by executing the programs listed
+in ($etcdir)/ssh_prng_cmds, reading their output and adding it to the

 PRNG supplied by OpenSSL (which is hash-based). It also stirs in the
 output of several system calls and timings from the execution of the
 programs that it runs.
 PRNG supplied by OpenSSL (which is hash-based). It also stirs in the
 output of several system calls and timings from the execution of the
 programs that it runs.


@@ -40,24 +44,23 @@ the specified program.
 
 The random number code will also read and save a seed file to
 ~/.ssh/prng_seed. This contents of this file are added to the random
 
 The random number code will also read and save a seed file to
 ~/.ssh/prng_seed. This contents of this file are added to the random

-number generator at startup.
+number generator at startup. The goal here is to maintain as much
+randomness between sessions as possible.

 
 

-This approach presents two problems:
+The default entropy collection code has two main problems:

 
 1. It is slow.
 
 
 1. It is slow.
 

-Executing each program in the list can take a large amount of time,   
-especially on slower machines. Additionally some program can take a   
-disproportionate time to execute.                                     
+Executing each program in the list can take a large amount of time,
+especially on slower machines. Additionally some program can take a
+disproportionate time to execute.

 
 

-This can be tuned by the administrator. To debug the entropy
-collection is great detail, turn on full debugging ("ssh -v -v -v" or
-"sshd -d -d -d"). This will list each program as it is executed, how
-long it took to execute, its exit status and whether and how much data
-it generated. You can the find the culprit programs which are causing
-the real slow-downs.
+Tuning the random helper can be done by running ./ssh-random-helper in
+very verbose mode ("-vvv") and identifying the commands that are taking
+excessive amounts of time or hanging altogher.  Any problem commands can
+be modified or removed from ssh_prng_cmds.

 
 

-The entropy collector will timeout programs which take too long
+The default entropy collector will timeout programs which take too long

 to execute, the actual timeout used can be adjusted with the
 --with-entropy-timeout configure option. OpenSSH will not try to
 re-execute programs which have not been found, have had a non-zero
 to execute, the actual timeout used can be adjusted with the
 --with-entropy-timeout configure option. OpenSSH will not try to
 re-execute programs which have not been found, have had a non-zero


@@ -78,3 +81,15 @@ up and various other factors.
 To make matters even more complex, some of the commands are reporting
 largely the same data as other commands (eg. the various "ps" calls).
 
 To make matters even more complex, some of the commands are reporting
 largely the same data as other commands (eg. the various "ps" calls).
 

+
+How to avoid the default entropy code?
+
+The best way is to read the OpenSSL documentation and recompile OpenSSL
+to use prngd or egd.  Some platforms (like earily solaris) have 3rd
+party /dev/random devices that can be also used for this task.
+
+If you are forced to use ssh-rand-helper consider still downloading
+prngd/egd and configure OpenSSH using --with-prngd-port=xx or
+--with-prngd-socket=xx (refer to INSTALL for more information).
+
+$Id$