DES ALGORITHMS

1. (DES)Data Encryption Standard:
A block cipher processes the plaintext
input in fixed-sized blocks and produces a
block of cipher text of equal size for each
plaintext block
The plaintext is 64 bits in length and the key
(k) is 56 bits in length (16 rounds of
processing (16 sub keys (k (left shift to k1)
k1…..k16 are generated for each round
based on left shift)
The plaintext block is divided into two
halves, LE0 and RE0. The two halves of the
data pass through 16 rounds of processing
and then combine to produce the cipher
text block.
A substitution is performed on the left half
of the data. This is done by applying a
round function F(left circular shift shuffles
the input block) to the right half of the data
and then taking the exclusive-OR (XOR) of

2. the output of that function and the left half
of the data.
Permutation is performed that consists of
the interchange of the two halves of the
data.

3. Implemtation of simple DES
Algorithm
Program:
import java.security.*; // Java Security
Packages There are three security-
related packages in java 1. JCA/JCE
(Java Cryptography Architecture & Java
Cryptography Extensions) 2. JSSE( Java
Secure-Sockets Extension). 3. JAAS( Java
Authentication & Authorization Service)
import javax.crypto.*; // Provides the
classes and interfaces for cryptographic
operations. Operation include
encryption, key generation and key
agreement, and Message Authentication
Code (MAC) generation.
public class PrivateExample

4. {
public static void main(String[] args)
throws Exception
{
if (args.length != 1)
{
System.err.println("Usage:Java
PrivateExample text");
System.exit(1);
}
byte[] plainText =
args[0].getBytes("UTF8"); /* 8-bit
Unicode Transformation Format */
System.out.println("n start generating
DES key");
KeyGenerator KeyGen =
KeyGenerator.getInstance("DES");
KeyGen.init(56);
Key key= KeyGen.generateKey();

5. System.out.println("n finish generating
DES key");
Cipher cipher=
Cipher.getInstance("DES/ECB/PKCS5Pa
dding");//electronic code book : public
key crypto standard 5
System.out.println("n"+cipher.getProvid
er().getInfo());
System.out.println("n start encryption ");
cipher.init(Cipher.ENCRYPT_MODE,ke
y);
byte[] cipherText =
cipher.doFinal(plainText);
System.out.println("Finish Encryption");
System.out.println(new
String(cipherText,"UTF8"));
System.out.println("n Start
Decryption");
cipher.init(Cipher.DECRYPT_MODE,ke
y);

6. byte[] newPlainText =
cipher.doFinal(cipherText);
System.out.println("Final decryption");
System.out.println(new
String(newPlainText, "UTF8"));
}
}
Output :