[Esapi-user] ESAPI Random Number Generation Broken

Jeff Williams jeff.williams at aspectsecurity.com
Sat Jun 28 02:16:41 UTC 2014


I found the problem.  The real problem.  There was a change introduced in StringUtilities r722 that broke the union() method.  This method was used to generate the EncoderConstants.CHAR_ALPHANUMERICS set used in the test case.

I've checked in a fix and test cases to verify that it works.  I also added a very simple test case for getRandomString() that verifies that the method generates roughly the same number of each character across a bunch of generated strings.  Not perfect but at least sensitive enough to recognize if something is way off.

The good news is that order has been restored to the universe, and our Burp test suite results are back to 'excellent'.  If you'd like to verify this yourself (and I strongly encourage you to do so) I included a small utility to generate random tokens as a main() method in RandomizerTest.

     * Run this class to generate a file named "tokens.txt" with 20,000 random 20 character ALPHANUMERIC tokens.
     * Use Burp Pro sequencer to load this file and run a series of randomness tests.
     * NOTE: be careful not to include any CRLF characters (10 or 13 ASCII) because they'll create new tokens
     * Check to be sure your analysis tool loads exactly 20,000 tokens of 20 characters each.
	public static void main(String[] args) throws IOException {
		FileWriter fw = new FileWriter("tokens.txt");
		for (int i = 0; i < 20000; i++) {
			String token = ESAPI.randomizer().getRandomString(20, EncoderConstants.CHAR_ALPHANUMERICS);
			fw.write(token + "\n");

Thanks to everyone who put some thought into the issue.


-----Original Message-----
From: Jim Manico [mailto:jim.manico at owasp.org] 
Sent: Thursday, June 26, 2014 1:30 AM
To: Kevin W. Wall
Cc: Jeff Williams; Bruno Girin; esapi-dev at lists.owasp.org; esapi-user at lists.owasp.org
Subject: Re: [Esapi-user] ESAPI Random Number Generation Broken

I'll track these issues on google code as soon as I get to a real computer. Everything you say makes perfect sense to me and I appreciate your time.

I'm still going to chase down DJB's SecureRandom hack for our analysis. (Dr) Steven Murdoch is here in Cambridge and made that suggestion.

Cheers, Kevin.
Jim Manico
(808) 652-3805

> On Jun 26, 2014, at 5:39 AM, "Kevin W. Wall" <kevin.w.wall at gmail.com> wrote:
>> On Wed, Jun 25, 2014 at 9:57 AM, Jim Manico <jim.manico at owasp.org> wrote:
>> PS: Java 8 improves upon this and provides a new API:
>> http://docs.oracle.com/javase/8/docs/api/java/security/SecureRandom.h
>> tml#getInstanceStrong-- which is what we should be using for " 
>> high-value/long-lived secrets like RSA public/private keys". But even 
>> then, using the same instance without reseeding with lead to a PRNG, 
>> not a CRNG sequence.
> That's all well and good, but even with JDK 7 and earlier, 
> SecureRandom
> *is* a CSRNG. (Note that a CSRNG *is* a PRNG.)  The problems with 
> SecureRandom very early own is that they just punted on the initial 
> pseudo-random seed. Before JDK 1.4 (I think that's where it was 
> changed), the first time they set the seed, they did some black magic 
> like mixing together a few bits from the current time in milliseconds, 
> the current amount of total and available memory in the Java heap, and 
> added in how many times a thread could yield in 3 seconds.  Near boot 
> time, all those things were very predictable. In 1.4 (maybe 1.3), it 
> was changed to initialize the seed /dev/urandom if it was available 
> and if not, I think it reverted to some other song and dance.  There 
> is problems however with /dev/urandom shortly after boot time (and 
> ESPECIALLY shortly after the *initial* system boot). Using /dev/random 
> would be better, but unfortunately that will block. (Aside: At my 
> previous job, we wrote an EntropyPool to seed things like SecureRandom 
> that would read from /dev/random by default or alternately 
> /dev/urandom. There was a warning in the Javadoc if would block and to 
> use the weaker entropy setting if that was a concern. It was never a 
> problem until one time when an application had a new release and they 
> started requesting [for some unknown reason] about 10k worth of data 
> from this EntropyPool all at once. And it was in an /etc/init.d script 
> that started their application in WebLogic Server. Result was they had 
> a 20+ minute startup delay until 10k bytes could be collected from 
> /dev/random. They called me in the middle of the night to 'yell' at 
> me. I nicely told them to RTFM. Sigh.)
> Anyway, my guess is that getInstanceStrong() method will allow you to 
> specify things like "use /dev/random".  However, I agree with Thomas 
> Ptacek's comment that if it really matters use an Operating 
> System-level CSRNG and not a userspace CSRNG. There are of course 
> reasons why you might not want to. Always using /dev/urandom is a 
> reasonable compromise, but there are still edge cases where you can 
> get burned by using /dev/urandom rather than /dev/random. But unless 
> you are protecting nuclear launch codes (and seriously, you BETTER not 
> be doing that with Java since you can't guarentee that you clear 
> memory), /dev/urandom will probably suffice.
> Also, one thing that I picked up on the Cigital blog post
> (http://www.cigital.com/justice-league-blog/2009/08/14/proper-use-of-j
> avas-securerandom/) was that an attacker could potentially hide a call 
> like this
>    System.setProperty("securerandom.source", "/dev/zero");
> in some 3rd party library that you are using and then your are toast.
> Of course, the same is true if you don't specify that you want the Sun 
> provider as in:
>    SecureRandom csrng = SecureRandom.getInstance("SHA1PRNG", "SUN");
> as someone could dynamically insert their own tainted provider for 
> SecureRandom into a 3rd party library you are using and again you are 
> screwed. (Unless of course you are using a Java SecurityManager and an 
> appropriately locked-down security policy which I am sure that you 
> *all* are doing, right. Cough, cough.)
> Anyhow, we need to do something about those two things in ESAPI...
> especially the first since it would be really subtle. Anyone care to 
> write up a Google issue to that effect to remind me?
> Cheers,
> -kevin
> --
> Blog: http://off-the-wall-security.blogspot.com/
> NSA: All your crypto bit are belong to us.

More information about the Esapi-user mailing list