Creating MessageDigest - 1

7 May 2008

Message digests are secure one-way hash functions that take arbitrary-sized data and output a fixed-length hash value. Thing to remember is that it I s not any encryption technique. It’s simply hashing. Same message will always generate the same hash code and a slight change in the message will generate completely different hash code. In the next few posts, I will talk about how we can generate message digests in our Java programmes.

The popular message digest algorithms are MD5 and SHA. java.security.MessageDigest class provides support for creating message digests. You are not supposed to implement the MD5v or SHA algorithms. MessageDigest class has all the needed umplementations.

Lets me show this through an example:

String str = "Hello World";
 
byte[] defaultBytes = str.getBytes();
 
MessageDigest algorithm = MessageDigest.getInstance("MD5");
algorithm.reset();
algorithm.update(defaultBytes);
byte messageDigest[] = algorithm.digest();
 
StringBuffer hexString = new StringBuffer();
 
for (int i=0;i<messageDigest.length;i++) {
String hex = Integer.toHexString(0xFF & messageDigest[i]);
if(hex.length()==1)
hexString.append('0');
hexString.append(hex);
}
 
System.out.println("String:  " + str);
System.out.println("MessageDigest: " + hexString.toString());

Output: 

String:  Hello World
MessageDigest: b10a8db164e0754105b7a99be72e3fe5

continued …

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