17 AES对密钥key长度的优化

1. 接上文，AES的密钥长度再底层定义了固定的长度，16，24，32.但是再实际生产情况下，可能会出现比较任意长度的密钥，如何处理？
2. 在获取加解密对象的时候特殊处理:

import com.yutu.pwd.util.HexUtils;
import org.junit.jupiter.api.Test;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.SecureRandom;
/**
 * Aes加密
 */
public class AESTest {
    private static final String UTF8 = StandardCharsets.UTF_8.name();

    //加密算法名称
    private static final String ALGORITHM = "AES";
    //AES默认的长度只有16，24，32
    private static final String KEY = "12345678abcdefghss";

    @Test
    public void S() throws Exception{
        String str = "小汪学java";
        //DES加密
        String encrypt = encrypt(str);
        System.out.println("16进制 + Aes 加密后的字符串： " + encrypt);
        System.out.println("------------------------");
        String decrypt = decrypt(encrypt);
        System.out.println("16进制 + Aes 解密后的字符串: " + decrypt);
    }

    /**
     * des加密
     * @param text 待加密的内容
     * @return
     */
    private String encrypt(String text) throws Exception{
        Cipher cipher = getCipher2(Cipher.ENCRYPT_MODE, KEY);
        //加密
        byte[] encodedBytes = cipher.doFinal(text.getBytes(UTF8));
        return HexUtils.covertBytes2HexStr(encodedBytes);
    }

    /**
     * 解密
     * @param encodedStr 加密后的字符串
     * @return
     * @throws Exception
     */
    private String decrypt(String encodedStr) throws Exception{
        byte[] bytes = HexUtils.convertHex2Bytes(encodedStr);
        //Cipher cipher = Cipher.getInstance(ALGORITHM);
        Cipher cipher = getCipher2(Cipher.ENCRYPT_MODE, KEY);
        SecretKey secretKey = new SecretKeySpec(KEY.getBytes(UTF8), ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE,secretKey);//解密模式
        //获取解码后的字节数组
        byte[] decryptBytes = cipher.doFinal(bytes);
        return new String(decryptBytes,UTF8);
    }

    /**
     * 获取Cipher对象
     * @param type  加解密模式
     * @param seed  密钥key
     * @return
     */
    private Cipher getCipher(int type,String seed) throws Exception{
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        SecretKey secretKey = new SecretKeySpec(seed.getBytes(UTF8), ALGORITHM);
        cipher.init(type,secretKey);//解密模式
        return cipher;
    }

    /**
     * 不管传递的是多少位长度的密钥,最后都会生成指定长度的密钥
     * @param type
     * @param seed
     * @return
     * @throws Exception
     */
    private Cipher getCipher2(int type,String seed) throws Exception{
        Cipher cipher = Cipher.getInstance(ALGORITHM);

        //获取KeyGenerator对象,可以根据传入的key生成一个指定长度的key
        KeyGenerator keyGenerator = KeyGenerator.getInstance(ALGORITHM);

        SecureRandom secureRandom = SecureRandom.getInstance("SHA1PRNG");//此处是生成key的规则算法
        secureRandom.setSeed(seed.getBytes(UTF8));

        keyGenerator.init(128,secureRandom);

        //通过keyGenerator生成新的密钥
        SecretKey secretKey = keyGenerator.generateKey();
        //获取新密钥的字节数组
        byte[] encoded = secretKey.getEncoded();

        SecretKey secretKeySpec = new SecretKeySpec(encoded, ALGORITHM);
        cipher.init(type,secretKeySpec);//解密模式
        return cipher;
    }
}