The Java Developers Almanac 1.4


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Home > List of Packages > javax.crypto  [14 examples] > Encrypting and Decrypting  [6 examples]

e463. Encrypting a File or Stream with DES

This example implements a class for encrypting and decrypting files or streams using DES. The class is created with a key and can be used repeatedly to encrypt and decrypt streams using that key.
    public class DesEncrypter {
        Cipher ecipher;
        Cipher dcipher;
    
        DesEncrypter(SecretKey key) {
            // Create an 8-byte initialization vector
            byte[] iv = new byte[]{
                (byte)0x8E, 0x12, 0x39, (byte)0x9C,
                0x07, 0x72, 0x6F, 0x5A
            };
            AlgorithmParameterSpec paramSpec = new IvParameterSpec(iv);
            try {
                ecipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
                dcipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
    
                // CBC requires an initialization vector
                ecipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
                dcipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
            } catch (java.security.InvalidAlgorithmParameterException e) {
            } catch (javax.crypto.NoSuchPaddingException e) {
            } catch (java.security.NoSuchAlgorithmException e) {
            } catch (java.security.InvalidKeyException e) {
            }
        }
    
        // Buffer used to transport the bytes from one stream to another
        byte[] buf = new byte[1024];
    
        public void encrypt(InputStream in, OutputStream out) {
            try {
                // Bytes written to out will be encrypted
                out = new CipherOutputStream(out, ecipher);
    
                // Read in the cleartext bytes and write to out to encrypt
                int numRead = 0;
                while ((numRead = in.read(buf)) >= 0) {
                    out.write(buf, 0, numRead);
                }
                out.close();
            } catch (java.io.IOException e) {
            }
        }
    
        public void decrypt(InputStream in, OutputStream out) {
            try {
                // Bytes read from in will be decrypted
                in = new CipherInputStream(in, dcipher);
    
                // Read in the decrypted bytes and write the cleartext to out
                int numRead = 0;
                while ((numRead = in.read(buf)) >= 0) {
                    out.write(buf, 0, numRead);
                }
                out.close();
            } catch (java.io.IOException e) {
            }
        }
    }
Here's an example that uses the class:
    try {
        // Generate a temporary key. In practice, you would save this key.
        // See also e464 Encrypting with DES Using a Pass Phrase.
        SecretKey key = KeyGenerator.getInstance("DES").generateKey();
    
        // Create encrypter/decrypter class
        DesEncrypter encrypter = new DesEncrypter(key);
    
        // Encrypt
        encrypter.encrypt(new FileInputStream("cleartext1"),
            new FileOutputStream("ciphertext"));
    
        // Decrypt
        encrypter.decrypt(new FileInputStream("ciphertext"),
            new FileOutputStream("cleartext2"));
    } catch (Exception e) {
    }

 Related Examples
e461. Listing All Available Encryption and Decryption Algorithms
e462. Encrypting a String with DES
e464. Encrypting with DES Using a Pass Phrase
e465. Converting a 56-bit Value to a DES Key
e466. Encrypting an Object with DES

See also: Key Agreement    MAC    Symmetric Keys   


© 2002 Addison-Wesley.