Generate a random password Post: 302139501

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Top Forums Shell Programming and Scripting Generate a random password Post 302139501 by Perderabo on Sunday 7th of October 2007 06:53:10 PM

10-07-2007

Administrator Emeritus

Quote:

Originally Posted by caiser

Whats wrong with:

[code]cat /dev/urandom| .....

Since you asked, the problems start with your use of /dev/urandom. As one example, see "Analysis of the Linux Random Number Generator", March 6, 2006 by Gutterman, Pinkas, and Reinman.

Quote:

Linux is the most popular open source project. The Linux random number generator is part of the kernel of all Linux distributions and is based on generating randomness from entropy of operating system events. The output of this generator is used for almost every security protocol, including TLS/SSL key generation, choosing TCP sequence
numbers, and file system and email encryption. Although the generator is part of an open source project, its source code (about 2500 lines of code) is poorly documented, and patched with hundreds of code patches. We used dynamic and static reverse engineering to learn the operation of this generator. This paper presents a description of the underlying algorithms and exposes several security vulnerabilities. In particular, we show an attack on the forward security of the generator which enables an adversary who exposes the state of the generator to compute previous states and outputs. In addition we present a few cryptographic flaws in the design of the generator, as well as measurements of the actual entropy collected by it, and a critical analysis of the use of the generator in Linux distributions on disk-less devices.

In addition, your generator will not constrain its output to produce passwords that are easy for a human to remember.

I really encourage anyone who thinks that they have a method of generating random passwords to formally test that assumption. My script's output has passed the Diehard suite. And here is a clue, you need a random number generator that can pass Diehard. I am not aware of any version of unix or linux that comes with any random number generator that can do that. Passing Diehard is tough. No linear congruential generator, such as rand(), will even come close.

Note that even if /dev/urandom is reengineered to output random numbers, the fact that other users on the system can examine the current state of the generator and then compute previous states continues to be a problem. You really need a method that will deliver a stream of random numbers to you and only to you.

Perderabo

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LEARN ABOUT LINUX

uuidgen

UUIDGEN(1)						      General Commands Manual							UUIDGEN(1)

NAME

       uuidgen - command-line utility to create a new UUID value

SYNOPSIS

       uuidgen [-r|-t]

DESCRIPTION

       The uuidgen program creates (and prints) a new universally unique identifier (UUID) using the libuuid(3) library.  The new UUID can reason-
       ably be considered unique among all UUIDs created on the local system, and among UUIDs created on other systems in  the	past  and  in  the
       future.

       There  are two types of UUIDs which uuidgen can generate: time-based UUIDs and random-based UUIDs.  By default uuidgen will generate a ran-
       dom-based UUID if a high-quality random number generator is present.  Otherwise, it will chose a time-based UUID.  It is possible to  force
       the generation of one of these two UUID types by using the -r or -t options.

OPTIONS

       -r     Generate	a  random-based UUID.  This method creates a UUID consisting mostly of random bits.  It requires that the operating system
	      have a high quality random number generator, such as /dev/random.

       -t     Generate a time-based UUID.  This method creates a UUID based on the system clock plus the system's ethernet  hardware  address,	if
	      present.

CONFORMING TO

       OSF DCE 1.1

AUTHOR

       uuidgen was written by Andreas Dilger for libuuid.

AVAILABILITY

       The uuidgen command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

SEE ALSO

       libuuid(3)

Linux								     May 2009								UUIDGEN(1)

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