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Tag Archives: Java

Java stuff

28-Nov-11

Here is some Java stuff I’ve written over the last year for Daily Fratze. All of the stuff is in use on Daily Fratze since June 2011.

java-akismet
java-akismet is a simple client for Akismet based on the latest version of Apache HttpComponents.
java-oembed
I really like the idea of oEmbed: A mechanism for auto embedding stuff from other sites so that users don’t have to paste some html code into a textbox but just plain links. This is my version of a configurable Java client that can autodetect oEmbed endpoints as well as statically configured endpoints.
java-autolinker
This is my idea of an autolinker based on jsoup. If you want to get autolinking right, you have to parse the text. Just scanning for regex that matches urls or email addresses is not enough. This autolinker first parses the text into a DOM tree and passes all text nodes to the configured linkers. At the moment it supports URLs, email addresses and twitter handles.

I’d be happy if someone can actually use this stuff too or even contribute to it :)

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MySql compatible AES encryption / decryption in Java

18-Jul-11

MySQL has an aes_encrypt/aes_decrypt pair of functions (Encryption and Compression Functions) that enable encryption and decryption of data using the official AES algorithm.

The functions are easy to use (select AES_ENCRYPT(‘text’,'password’)) and the result is easy to store (insert into secrets values HEX(AES_ENCRYPT(‘text’,'password’))) as hex values.

I used this technique for a while but i wanted to have a more database agnostic version of this encryption and tried to build the same methods with java.

Although it was relatively easy to find the exact cipher mode (which is AES/ECB/PKCS5Padding), i had a real hard time figuring out how the key is calculated from the given password (the key must be 16bytes long, per default MySql uses AES-128). It turns out that the MySQL algorithm just or’s the bytes of a given passphrase against the previous bytes if the password is longer than 16 chars and just leaves them 0 when the password is shorter than 16 chars. So you can generate a secret key spec in Java for an aes_encrypt/decrypt compatible cipher like so:

import java.io.UnsupportedEncodingException;
 
import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
 
import org.apache.commons.codec.binary.Hex;
 
public class Demo {
	public static SecretKeySpec generateMySQLAESKey(final String key, final String encoding) {
		try {
			final byte[] finalKey = new byte[16];
			int i = 0;
			for(byte b : key.getBytes(encoding))
				finalKey[i++%16] ^= b;			
			return new SecretKeySpec(finalKey, "AES");
		} catch(UnsupportedEncodingException e) {
			throw new RuntimeException(e);
		}
	}
 
	public static void main(String... args) throws Exception {
		// Decrypt
		final Cipher decryptCipher = Cipher.getInstance("AES");	        				
		decryptCipher.init(Cipher.DECRYPT_MODE, generateMySQLAESKey("your super secret passphrase", "UTF-8"));
		System.out.println(new String(decryptCipher.doFinal(Hex.decodeHex("56A34D7AB6225616799F6559AA388F07C2C9E53983111BDD5F49F36461AAD789".toCharArray()))));
 
		// Encrypt
		final Cipher encryptCipher = Cipher.getInstance("AES");	        				
		encryptCipher.init(Cipher.ENCRYPT_MODE, generateMySQLAESKey("your super secret passphrase", "UTF-8"));		
		System.out.println(String.format("Select aes_decrypt(unhex('%s'), 'your super secret passphrase');", new String(Hex.encodeHex(encryptCipher.doFinal("Hallo nach Aachen".getBytes("UTF-8")))))); 
	}
}

You need Commons Codec to run these.

This isn’t probably the most secure solution from a cryptographic point of view but it just replicates the built-in MySql function for other databases or just for interoperability. I hope to save someone else time with this as i spent about days about those view lines.

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Different day, same shit, today: Java 5 on Oracle Enterprise Linux 5

19-Jan-09

Worlds collide: Oracle and Sun JDK. Perfect start to ruin a not so bad Monday morning.

Background: Need to have a Tomcat Server deployed on a Oracle Enterprise Linux 5 system.

I was happy, when i saw a tomcat5 package in the repositories. Great, i thought. All i need. Well. Not.

Under Windows you’ll get between one and ten JVM versions installed with on Oracle product (slight exaggerated), within the OEL5 there was only one ancient 1.4.2 JDK. *sigh* Did i mention that the application that is supposed to run on that thing uses a buttload of Java 5 features?

“yum search java-”… No Java 5. WtF?

There is no Java 5.

Again, do it yourself:

This is a nice entry that describes howto build rpms for the “official” Sun Java 5 jdk.

I used the following steps to build my rpms:

  • Downloaded this rpm
  • Downloaded jdk-1_5_0_15-linux-i586.bin from the Sun JDK archive page
  • Put the later one into /usr/src/redhat/SOURCES/
  • Built the rpms with rpmbuild –rebuild java-1.5.0-sun-1.5.0.15-1jpp.nosrc.rpm. If rpmbuild is not installed, it’s hidden in the package rpm-build, not rpmbuild.
  • Installed missing libXp
  • Installed the rpms: 
    rpm -Uvh /usr/src/redhat/RPMS/i586/java-1.5.0-sun-1.5.0.15-1jpp.i586.rpm
rpm -Uvh /usr/src/redhat/RPMS/i586/java-1.5.0-sun-devel-1.5.0.15-1jpp.i586.rpm
rpm -Uvh /usr/src/redhat/RPMS/i586/java-1.5.0-sun-src-1.5.0.15-1jpp.i586.rpm
rpm -Uvh /usr/src/redhat/RPMS/i586/java-1.5.0-sun-demo-1.5.0.15-1jpp.i586.rpm
rpm -Uvh /usr/src/redhat/RPMS/i586/java-1.5.0-sun-plugin-1.5.0.15-1jpp.i586.rpm
rpm -Uvh /usr/src/redhat/RPMS/i586/java-1.5.0-sun-fonts-1.5.0.15-1jpp.i586.rpm
rpm -Uvh /usr/src/redhat/RPMS/i586/java-1.5.0-sun-alsa-1.5.0.15-1jpp.i586.rpm
rpm -Uvh /usr/src/redhat/RPMS/i586/java-1.5.0-sun-jdbc-1.5.0.15-1jpp.i586.rpm
  • Last step: Choose the right java version with alternatives –config java

After that, everything could be fine. Well, it wasn’t:

sun.misc.InvalidJarIndexException: Invalid index

Jehova! Finally not a NPE but something new, at least to me. Sometimes i wonder why i always run into bugs like these.

Some script changes and repackages all jar files in some weird ways so that a standard JDK has funny problems.

My solution to it: Reindex everything in /usr/share/java after you’ve chosen your newly installed java with the following command:

find /usr/share/java/ -iname "jakarta*commons*.jar" -exec jar -i {} \;

I opted to reindex only the jakarta commons files, that got Tomcat up and running with Java 5.

One last note: The /usr/bin/dtomcat5 is broken imho, at least when run from /etc/init.d/tomcat5. In ignores /etc/tomcat5/tomcat5.conf and therefore cannot stop Tomcat.

My solution: Replace

if [ -z "$CATALINA_HOME" ]; then
    TOMCAT_CFG="/etc/tomcat5/tomcat5.conf"
fi

(in line 55 on my setup) with

if [ -z "$CATALINA_HOME" ]; then
    TOMCAT_CFG="/etc/tomcat5/tomcat5.conf"
    [ -r "$TOMCAT_CFG" ] && . "${TOMCAT_CFG}"
fi

and remove

if [ -z "$CATALINA_HOME" ]; then
    [ -r "$TOMCAT_CFG" ] && . "${TOMCAT_CFG}"
fi

(in line 105 on my setup).

I wonder why simple things like these always are a pain in the ass. Stupid nuisances that keeps people from getting their work done. *sigh* Not a good start for the week.

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Division by zero

26-May-08

Just a quick reminder for myself:

int a = 0/0; // Throws ArithmeticException
double d1 = 0/0.0; // d1 is NaN
double d2 = 1/0.0; // d2 is Infinity
double d3 = -1/0.0; // d3 is -Infinity

Can cause some headache if things fall apart in the JDBC driver and not before. Grmpf.

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SCJP, finally!

06-May-08

More than a year ago i decided to do the Sun Certified Java Programmer. Shortly after i bought this book, the projects at work and at home were somewhat overwhelming and after all, i realized that a big part of the SCJP is about some weird, crazy and sometimes wrong design decisions of the Java language. Some of them i mentioned under this tag.

Last month i realized i had some spare time, signed up at Prometric and had a 2nd look at the book and on my good Java experience from the last 6 years.

First thing: The “Java 5 Study Guide” isn’t a bad book but the “MasterExam” software on the enclosed cd is a master piece of crap. Not only the gui is as shitty as it gets but some of the answers are just plain wrong.

Second thing: I bought the preparation kit from Whizlabs for 50€. This thing isn’t bad at all and helps you get prepared for the craziness thrown at you.

Third: Being good at something is always great :D It rocks, really. Like single trail riding or music with electric guitars while driving open. It’s like drugs but not that unhealthy.

After about 2 weeks of preparing, I arrived 30 minutes early at “New Horizons” in Cologne, took the test certainly in english as i prepared with english material and finished somewhat 50 minutes later (you have officially around 3 hours to take the test). The nice proctor asked me if i wanted to use the toilet as she saw my report being printed: 90%, pass! Wooot!

I thought about this post at Jans. I really like the guy who wins a million dollars at Who wants to be a Millionaire and has the guts to call his dad but not ask for help and instead tells him he is going to win a million dollars. I can totally relate to that as i always had fun taking test and scoring at the upper limit :D

So today i’m gonna eat an extra portion of Cookies & Cream and leave you with the following piece of Java madness:

More…

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