Triples Data Encryption Standard (3DES)

 

1.what's DES

   Definition:对称算法，数据加密标准，速度较快，适用于加密大量数据的场合。

2.what's 3DES

   Definition:基于DES的对称算法，对一块数据用三个不同的密钥进行三次加密，强度更高。

   Algorithm:

Triple DES uses a "key bundle" which comprises three DES , K₁, K₂ and K₃, each of 56 bits (excluding ). The encryption algorithm is:

ciphertext = E_K3(D_K2(E_K1(plaintext)))

I.e., DES encrypt with K₁, DES decrypt with K₂, then DES encrypt with K₃.

Decryption is the reverse:

plaintext = D_K1(E_K2(D_K3(ciphertext)))

I.e., decrypt with K₃, encrypt with K₂, then decrypt with K₁.

Each triple encryption encrypts of 64 bits of data.

The standards define three keying options:

• Keying option 1: All three keys are independent.
• Keying option 2: K₁ and K₂ are independent, and K₃ = K₁.
• Keying option 3: All three keys are identical, i.e. K₁ = K₂ = K₃.

eg:

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;

public class Des {
   
    private static final String Algorithm = "DESede";
    public static final byte[] keyBytes = {0x11, 0x22, 0x4F, 0x58, (byte)0x88, 0x10, 0x40, 0x38
                , 0x28, 0x25, 0x79, 0x51, (byte)0xCB, (byte)0xDD, 0x55, 0x66
                , 0x77, 0x29, 0x74, (byte)0x98, 0x30, 0x40, 0x36, (byte)0xE2};  
    //24字节的密钥
   
   /*
     * @ use DESede algorithm to encrpty the src
     * @ keybyte: secretkey 24 byte
     * @ src:the text needs to be encrypt
     * @ return the enc result
     */
    public static byte[] encryptMode (byte[] keybyte, byte[] src) {
        try {
            SecretKey deskey = new SecretKeySpec (keybyte, Algorithm);
            Cipher c1 = Cipher.getInstance ("DESede/ECB/PKCS5Padding");
            c1.init (Cipher.ENCRYPT_MODE, deskey);
            return c1.doFinal (src);
        } catch (java.security.NoSuchAlgorithmException e1) {
            e1.printStackTrace ();
        } catch (javax.crypto.NoSuchPaddingException e2) {
            e2.printStackTrace ();
        } catch (java.lang.Exception e3) {
            e3.printStackTrace ();
        }
        return null;
    }
   
    /*
     * @ use DESede algorithm to decrypt the src
     * @ keybyte: secretkey 24 byte
     * @ src:the text needs to be dec
     * @ return the dec result
     */
    public static byte[] decryptMode (byte[] keybyte, byte[] src) {
        try {
            SecretKey deskey = new SecretKeySpec (keybyte, Algorithm);
            Cipher c1 = Cipher.getInstance ("DESede/ECB/PKCS5Padding");
            c1.init (Cipher.DECRYPT_MODE, deskey);
            return c1.doFinal (src);
        } catch (java.security.NoSuchAlgorithmException e1) {
            e1.printStackTrace ();
        } catch (javax.crypto.NoSuchPaddingException e2) {
            e2.printStackTrace ();
        } catch (java.lang.Exception e3) {
            e3.printStackTrace ();
        }
        return null;
    }
}