True Random Number Generator for a True Hacker

This is an interesting way to generate a sufficiently random number. We will definitely be adopting this technique for our products that need a non-cryptographic random number generator.

Hackaday

How can you generate random bits? Some people think it’s not easy, others will tell you that it’s pretty damn hard, and then there are those who wonder if it is possible at all. Of course, it is easy to create a very long pseudorandom sequence in software, but even the best PRNG (Pseudorandom Number Generator) needs a good random seed, as we don’t want to get the same sequence each time we switch on the unit, do we? That’s why we need a TRNG (True Random Number Generator), but that requires special hardware.

Some high-end microprocessors are equipped with an internal hardware TRNG, but it is, unfortunately, not true for most low-cost microcontrollers. There are a couple of tricks hackers use to compensate. They usually start the internal free running counter and fetch its contents when some external event occurs (user presses a button, or so). This works, but not without disadvantages…

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PHP-MCRYPT and Ubuntu 14.04 LTS

There is a weird problem with a default Ubuntu 14.04 LTS server installation. For some reason, php-mcrypt couldn’t run when running under FCGI mode using spawn-fcgi. It was correctly installed and configure but it is not detected correctly even under phpinfo();

However, everything seems to be work right after switching over to php-fpm instead of fcgi mode. I don’t know why.

Internships at AESTE

Listen to one of the interns at AESTE talk a little about his internship experience there.

  1. The work we do is HARD – but fruitful.
  2. The working culture is different – in a good way.
  3. You get to meet other interesting people – who will enrich you.

An internship at AESTE is guaranteed to push you to discover strange new things about yourself.

Read what other interns learned through their experiences here.

Apply now!

Securing My Blog

In order to improve the security of my blog, I have tried a few measures.

A while ago, I bought a Yubi-Key, which generates a one-time-password to be used alongside the regular login. This provided two-factor authentication and it was certainly working for a while. Then, I read up more about the Yubi-Key and found that there might be holes in the implementation of the plugin since it is still quite a new product and relatively untested.

So, I switched to using VPN instead. I configured my web-server to reject all attempts to access the administrative pages unless the connection originated from the local server. Then, I would use SSH to create a tunnel into the server and secure my connection through SSH keys. This also required two-factor authentication and provided the additional fact that the entire connection was secured over SSH.

I added this to my lighttpd configuration.

# Deny access to wordpress admin pages
$HTTP["host"] =~ "blog.sybreon.com|tech.sybreon.com" {
$HTTP["remoteip"] !~ "213\.229\.116\.90$" {
$HTTP["url"] =~ "^/wp-admin/|^/server-" {
url.access-deny = ("")
}
}
}

However, I had troubles accessing my blog from certain places because they blocked SSH connections.

Finally, I switched to SSL instead. I have now configured my web-server to only accept connections that present a valid security certificate over SSL. Again, this is a two-factor authentication using SSL certificates. Once again, the connection is also secured over SSL. I park my web server behind a pound reverse-proxy. So, this is the way I did it.

ListenHTTP
Address ::
Port 80
## allow PUT and DELETE also (by default only GET, POST and HEAD)?:
xHTTP 0

Service
URL "^(?!/wp-admin).*"
HeadRequire "Host:.*(blog|tech).sybreon.com"
BackEnd
Address ::1
Port 8080
End
End

End

ListenHTTPS
Address ::
Port 443

Cert "/etc/ssl/private/blog.crt"
CAlist "/etc/ssl/private/sybreon.ca.asc"
VerifyList "/etc/ssl/private/sybreon.ca.asc"
Ciphers "HIGH"
ClientCert 2 3

Service
HeadRequire "Host:.*(blog|tech).sybreon.com"
BackEnd
Address ::1
Port 8080
End
End
End

What this does is to reject all connections to the admin pages for my blogs if they came over regular HTTP and to only allow connections over HTTPS. However, for HTTPS connections, client certifications are required, which are signed by a my own custom CA. Otherwise, the connection will fail if a client certificate is not presented.

The advantage of doing it this way is that I can actually have collaborators. All I need to do is to generate new certificates for them and email it to them. This process can even be automated if need be.

PS: You can try accessing the admin page over HTTP and HTTPS here, to see how this works.

Multi-core Parallelism

As I mentioned in a previous blog, I am running a six-core machine – it is actually a virtual machine. Regardless, I noticed one thing while doing it. As I went from single-core to six-core, performance improved accordingly. But when I went up to eight-core, things deteriorated. The reason for this is probably because of the arrangement of the processors. I am running a two-socketed six-core AMD system. So, for an eight-core machine to work, it would need to cross sockets, which is not a good idea due to the communications hierarchy.

So, that’s why I ended up using a six-core VM.

Trust and Verify

I had a chat with my boss the other day, about how good software should be developed. He mentioned that we should use unit-testing and I told him that it was rubbish. Then, he mentioned TDD where tests are written before the actual application and I told him that he risked lying to himself about the quality of the code developed.

Okay, while this is not an entry bashing software testing, I will highlight why testing fails. As one prominent computer security researcher points out:

One researcher with three computers shouldn’t be able to do beat the efforts of entire teams, Miller argued. “It doesn’t mean that they don’t do [fuzzing], but that they don’t do it very well.”

This is because we end up relying on tools to do the testing. Not that there are anything wrong with tools, but the tools are only as good as their operators and the problem lies with the tool operator. When tools are used, the operators generally are either less astute or become lazy. They start to rely on the tool to catch problems and if the tool fails to catch any, they rely on the tool to sign-off on the quality of the code. Tools are inanimate objects and should not be liable for the stuff that they test. The tool operator should always dig in manually to verify the results. Through my 20+ years of active programming, I have been caught by tools so many times and I have developed a distinct distrust towards any tool. I even verify my compiler outputs by disassembling the binaries and checking them by hand once, before running them through a simulator to observe the operations.

objdump -dSC

I argued with my boss that there is only one way to develop good code, that is to just frakin’ write good code, which is not as hard as some people imagine it to be. Writing good code is like writing good prose, there are certain styles that can be followed that will result in better code. Unfortunately, good writing habits are hard to develop and need to be hammered into our apprentices from the very get go. Our universities are failing in this by not driving this point home and trying to teach our programmers to be ever more lazy and rely on automated tools to generate code instead. Okay, code generation is a whole different can of worms and I won’t bother to go into.

I have seen several senior engineers do, what I call, haphazard coding that results in code that sort-of works but without anyone knowing why. A slight change in any part of the code, even in the compiler optimisation settings, can bork out the code. This is usually the result of cut-and-paste coding styles and ineffectual debugging skills. I had to teach my CODE8 apprentice that in debugging, you always follow the flow of the data. There was one instance where I asked her to show me the result that is obtained from the LDAP query and she modified her code to output the data onto the web-application. Unfortunately, this involved obtaining the result from the LDAP query, extracting the relevant fields, reformatting the text before sending it out to the web-app. I then explained to her that this was not the output of the LDAP query. This was the output of the query after several processing steps. Garbage-in-garbage-out. If we do not know that the LDAP query output is accurate, how can we be sure that the reformatting and extraction routines are not frakin’ things up.

In the realm of hardware design, good coding practices are generally easier to enforce because if your code sucks, the hardware tools are not smart enough to do what you want and will usually just bork out. However, if the code is badly written, but just good enough to be understood by the synthesisers the tools will just end up producing very bad hardware design, which will suck up power and slow down performance. As a result, hardware coders are told to only write code in one specific way, in order to produce the hardware that we desire. We get these coding practices drummed into us in a class usually called – design for synthesis.

As for me, I tend to step through code line-by-line in order to see if it is doing what it is supposed to do. Unfortunately, with a language like Java, that can be very difficult to do because of the added complexity of the virtual machine layer. You can compile Java code into bytecode and inspect the bytecode but you won’t know if the JVM will actually run your bytecode the way it is meant to be run because you will just have to trust it to do so.

I subscribe to the principle – “trust and verify”.

Polipo DNS Issues

I have been using polipo as my proxy server and recently, it has been developing some weird problems. For one thing, it sometimes refuses to connect to websites without any errors on the client side except for time-outs. I know that the sites are up because I can connect to them if I bypass polipo.

The reason that I use polipo is because of resource requirements – much less than say, squid. As an upstream web proxy, it works really well. I have gotten better results out of it than squid but I simply put that down to my lack of squid config-fu. Polipo is much easier to configure as there are less options to play. However, it is also a plain vanilla proxy and does not try to become the proxy for everything as squid does.

After some investigation, I got a clue from the polipo logs – that it was timing out as well with the following message:

Host ftp.osuosl.org lookup failed: Timeout (131072).

This confused me because it was obvious that the website was up and working. So, I dug around and found out that polipo uses its own DNS resolver by default and not the system resolver. The reason that it does this is in order to obtain the TTL information on the domain directly. However, the information still comes from the same DNS server either way.

Turns out that it was a networking problem. By default, polipo would return the AAAA record instead of the A one if both are present. It is designed to prefer IPv6 over IPv4. My home network is IPv6. This can be controlled with either of the following options:

dnsQueryIPv6 = no
dnsQueryIPv6 = reluctantly

Since I have not yet enabled IPv6 support through my gateway, I decided to just disable IPv6 for polipo entirely. I might turn it back on once I get IPv6 up at home. I really need to get down to activating my Hurricane gateway tunnel and writing a guide for it.