The MD5 algorithm is a widely used hash function producing a 128-bit hash value. Although MD5 was initially designed to be used as a cryptographic hash function, it has been found to suffer from extensive vulnerabilities. It can still be used as a checksum to verify data integrity, but only against unintentional corruption.

You can easily extend Informix with your own built in MD% function written in Java.

1 Source code

The following code provides the md5 hash of a string

Copy

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class md5 {

	public static String getMD5(String text) 
		throws NoSuchAlgorithmException
	{
		MessageDigest algorithm = MessageDigest.getInstance("MD5");
		algorithm.reset();
		byte[] data = text.trim().getBytes();
		algorithm.update(data, 0, data.length);
		return __convert(algorithm.digest());
	}

	/**
	* Convert a byte array into a printable format containing a
	* String of hexadecimal digit characters (two per byte).
 	*
	* @param bytes Byte array representation
	*
	* public cause required by function_crypt_digest_sha ...
	*/
	private final static String __convert(byte bytes[])
	{
		StringBuilder sb = new StringBuilder(bytes.length * 2);
		for (int i = 0; i < bytes.length; i++) {
		    sb.append(convertDigit((int) (bytes[i] >> 4)));
		    sb.append(convertDigit((int) (bytes[i] & 0x0f)));
		}
		return (sb.toString());
	}

	/**
	* [Private] Convert the specified value (0 .. 15) to the corresponding
	* hexadecimal digit.
	*
	* @param value Value to be converted
	*/
	private final static char convertDigit(int value)
	{
		value &= 0x0f;
		if (value >= 10)
		    return ((char) (value - 10 + 'a'));		// lowercase
		else
		    return ((char) (value + '0'));
	}
}

2 Compile

Compile the source code and pack the class into a jar file.

Copy

$ javac -source 1.7 -target 1.7 md5.java
$ jar cvf md5.jar md5.class

3 Install

Execute the following SQL in the database where you want to install the routine.

Copy

BEGIN WORK;

EXECUTE PROCEDURE sqlj.install_jar ("file:$INFORMIXDIR/extend/krakatoa/examples/md5.jar", "md5_jar", 0);

CREATE FUNCTION MD5(lvarchar)
  RETURNS CHAR(32)
  EXTERNAL NAME 'md5_jar:md5.getMD5'
  LANGUAGE JAVA; 

GRANT EXECUTE ON FUNCTION MD5(lvarchar) TO ALL;

COMMIT WORK;

To run install_jar you need to have at least one Java virtual processor (JVP). If not, you will get the following error:

Copy

EXECUTE PROCEDURE sqlj.install_jar("file:$INFORMIXDIR/extend/krakatoa/examples/md5.jar", "md5_jar", 0);
#                                          ^
# 9799: User Defined Routine (install_jar) VP context switch failed.
#
#

To check available JVP processors check onstat -g glo for class jvp

4 Remove

Drop the MD5 function
Copy
```
DROP FUNCTION MD5(lvarchar);
```

Drop the MD5 jar

Copy

EXECUTE PROCEDURE sqlj.remove_jar('md5_jar');

5 Update

To update the MD5 java UDR use

Copy

EXECUTE PROCEDURE sqlj.replace_jar ("file:$INFORMIXDIR/extend/krakatoa/examples/md5.jar", "md5_jar");

6 Testing

When testing we will get the following error as the security module is not installed by default in the IBM jre.

Copy

SELECT tabname[1,18], MD5(tabname) FROM systables ORDER BY 1;

Unknown throwable: (java.security.NoSuchAlgorithmException: MD5 MessageDigest not available)