Melvin Carvalho http://melvincarvalho.com/blog Tue, 29 Dec 2009 22:15:49 +0000 http://wordpress.org/?v=2.9 en hourly 1 Installed F2F Plugin http://melvincarvalho.com/blog/installed-f2f-plugin/ http://melvincarvalho.com/blog/installed-f2f-plugin/#comments Tue, 29 Dec 2009 22:14:38 +0000 akkie http://melvincarvalho.com/blog/?p=38 Installed the F2F Plugin

]]> http://melvincarvalho.com/blog/installed-f2f-plugin/feed/ 0 Blog Upgraded http://melvincarvalho.com/blog/blog-upgraded/ http://melvincarvalho.com/blog/blog-upgraded/#comments Tue, 29 Dec 2009 12:03:10 +0000 melvincarvalho http://melvincarvalho.com/blog/?p=29 Upgraded to WP 2.9 and also OpenID plugin.

Now all we need is foaf+ssl!

]]> http://melvincarvalho.com/blog/blog-upgraded/feed/ 1 Solution to the Halting Problem http://melvincarvalho.com/blog/solution-to-the-halting-problem/ http://melvincarvalho.com/blog/solution-to-the-halting-problem/#comments Sun, 01 Nov 2009 22:20:21 +0000 akkie http://melvincarvalho.com/blog/?p=26 The following is a solution to the halting problem, which asks the question: given a description of a program, decide whether the program finishes running or will run forever. This problem is generally believed to be insoluble, however I believe it is possible to conceive a theoretical solution as follows.


Consider a thought experiment, in which quantum scientists, though sub atomic particle tunneling are able to perform a single logical operation in zero time.  Using this technology they are able to construct a quantum computer which is able to run sequential operation in zero time.  This quantum computer is set up as follows:  a light bulb goes on while the program is loaded into the computer.  The start button is pressed, and the computer starts to execute the program.  As soon as the lightbulb goes off, the program is finished and you can look at the result as well as the time taken to complete.  Now it is immediately apparent that the light bulb will go off after zero time if the program halts.  It is also easy to imagine that the machine keeps on processing if the program enters an infinite loop and the lightbulb will remain on.  Iff we observe that the lightbulb remains on we know that the program does not halt.  Hence we have a theoretical solution to the halting problem.


QED

]]> http://melvincarvalho.com/blog/solution-to-the-halting-problem/feed/ 1 Architecture of Web 3.0 http://melvincarvalho.com/blog/architecture-of-web-30/ http://melvincarvalho.com/blog/architecture-of-web-30/#comments Tue, 28 Apr 2009 06:28:47 +0000 akkie http://melvincarvalho.com/blog/?p=23 A great diagram that explains the fundamentals of Web 3.0.

]]> http://melvincarvalho.com/blog/architecture-of-web-30/feed/ 1 Enabling a Public Apache Server to Read a Client Certificate http://melvincarvalho.com/blog/enabling-a-public-apache-server-to-read-a-client-certificate/ http://melvincarvalho.com/blog/enabling-a-public-apache-server-to-read-a-client-certificate/#comments Wed, 10 Dec 2008 14:54:26 +0000 melvincarvalho http://melvincarvalho.com/blog/?p=8 The following is a recipe to configure an Apache Web Server to accept and read a self-signed SSL client certificates. This is one of the steps to implement the FOAF + SSL protocol as outlined by Henry Story.

1. Starting assumption is that your Apache server has SSL installed and working.

If not this is covered in depth in many other places, the easiest way is to contact your web hoster to get this done.

2. Change tha Apache httpd.conf to enable client certificates

You will need editing rights on your httpd.conf. Here are the changes I made in order to get things working:

SSLVerifyClient optional_no_ca
SSLVerifyDepth 1

Note: SSLCACertificateFile is not set so self signed certificates are not checked against the trusted CA’s configured on the server.

3. Add the following to the .htaccess to make the SSL variables available to php

SSLOptions +StdEnvVars
SSLOptions +ExportCertData

4. How to test it

The following code should be able to print out diagnostic information:

print_r($_SERVER);
print_r(openssl_x509_parse($_SERVER[SSL_CLIENT_CERT]))

An example can be seen here: https://foaf.me/test.php


If you think there’s a way to improve any of these steps please feel free to let me know.

]]> http://melvincarvalho.com/blog/enabling-a-public-apache-server-to-read-a-client-certificate/feed/ 2 25 November http://melvincarvalho.com/blog/hello-world/ http://melvincarvalho.com/blog/hello-world/#comments Tue, 25 Nov 2008 14:48:09 +0000 admin http://melvincarvalho.com/blog/?p=1 On this day in history I started a blog, JFK was buried and, “Do they know it’s Chirstmas” was recorded.

One said to “Feed the world”, the other “Together let us expore the stars, conquer the deserts, eradicate disease, tap the ocean depths, and encourage the arts and commerce”.

I beleive we can make this happen.  The board is set, the pieces are in motion!

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