密钥加密也称为对称加密，速度快，但加密和解密的钥匙必须相同，只有通信双方才能知道钥匙。

import java.security.Key;    import java.security.SecureRandom;        import javax.crypto.Cipher;    import javax.crypto.KeyGenerator;    import javax.crypto.SecretKey;    import javax.crypto.SecretKeyFactory;    import javax.crypto.spec.DESKeySpec;    import javax.crypto.spec.IvParameterSpec;        /**    * DES 算法       1972美国IBM研制，对称加密算法    * @author stone    * @date 2014-03-10 04:47:05    */    public class DES {          // 算法名称        public static final String KEY_ALGORITHM = "DES";        // 算法名称/加密模式/填充方式        public static final String CIPHER_ALGORITHM_ECB = "DES/ECB/PKCS5Padding";        public static final String CIPHER_ALGORITHM_CBC = "DES/CBC/PKCS5Padding";                public static void main(String[] args) throws Exception {            /*            * 使用 ECB mode            * 密钥生成器 生成密钥            * ECB mode cannot use IV            */            byte[] key = generateKey();             byte[] encrypt = encrypt("胃炎F#*（x）".getBytes(), key);            System.out.println(new String(decrypt(encrypt, key)));                                    /*            * 使用CBC mode            * 使用密钥工厂生成密钥，加密 解密            * iv: DES in CBC mode and RSA ciphers with OAEP encoding operation.            */            DESKeySpec dks = new DESKeySpec(generateKey());            SecretKeyFactory factory = SecretKeyFactory.getInstance(KEY_ALGORITHM);            SecretKey secretKey = factory.generateSecret(dks);            Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM_CBC);            cipher.init(Cipher.ENCRYPT_MODE, secretKey, new IvParameterSpec(getIV()));            byte[] enc = cipher.doFinal("胃炎A%F#*（x）".getBytes()); //加密                        cipher.init(Cipher.DECRYPT_MODE, secretKey, new IvParameterSpec(getIV()));            byte[] dec = cipher.doFinal(enc); // 解密            System.out.println(new String(dec));        }                static byte[] getIV() {            String iv = "asdfivh7"; //IV length: must be 8 bytes long            return iv.getBytes();        }            /**        * 生成密钥        *         * @return        * @throws Exception        */        private static byte[] generateKey() throws Exception {            KeyGenerator keyGenerator = KeyGenerator.getInstance(KEY_ALGORITHM);            keyGenerator.init(56); //des 必须是56, 此初始方法不必须调用            SecretKey secretKey = keyGenerator.generateKey();            return secretKey.getEncoded();        }            /**        * 还原密钥        *         * @param key        * @return        * @throws Exception         */        private static Key toKey(byte[] key) throws Exception {            DESKeySpec des = new DESKeySpec(key);            SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(KEY_ALGORITHM);            SecretKey secretKey = keyFactory.generateSecret(des);            return secretKey;        }                /**        * 加密         * @param data 原文        * @param key        * @return 密文        * @throws Exception        */        public static byte[] encrypt(byte[] data, byte[] key) throws Exception {            Key k = toKey(key);            Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM_ECB);            cipher.init(Cipher.ENCRYPT_MODE, k, new SecureRandom());            return cipher.doFinal(data);        }        /**        * 解密        * @param data 密文        * @param key        * @return 明文、原文        * @throws Exception        */        public static byte[] decrypt(byte[] data, byte[] key) throws Exception {            Key k = toKey(key);            Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM_ECB);            cipher.init(Cipher.DECRYPT_MODE, k, new SecureRandom());            return cipher.doFinal(data);        }    }