java – 为什么使用AES加密16个字节时,密文长度为32个字节？

发布时间：2020-12-14 05:32:38 所属栏目：Java 来源：网络整理

导读：我使用加密AES算法,当我加密16字节(一个块),结果是32字节. 这个可以吗？我使用的源代码是： package net.sf.andhsli.hotspotlogin;import java.security.SecureRandom;import javax.crypto.Cipher;import javax.crypto.KeyGenerator;import javax.crypto.Se

我使用加密AES算法,当我加密16字节(一个块),结果是32字节.
这个可以吗？

我使用的源代码是：

package net.sf.andhsli.hotspotlogin;

import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

/**
 * Usage:
 * <pre>
 * String crypto = SimpleCrypto.encrypt(masterpassword,cleartext)
 * ...
 * String cleartext = SimpleCrypto.decrypt(masterpassword,crypto)
 * </pre>
 * @author ferenc.hechler
 */
public class SimpleCrypto {

    public static String encrypt(String seed,String cleartext) throws Exception {
        byte[] rawKey = getRawKey(seed.getBytes());
        byte[] result = encrypt(rawKey,cleartext.getBytes());
        return toHex(result);
    }

    public static String decrypt(String seed,String encrypted) throws Exception {
        byte[] rawKey = getRawKey(seed.getBytes());
        byte[] enc = toByte(encrypted);
        byte[] result = decrypt(rawKey,enc);
        return new String(result);
    }

    private static byte[] getRawKey(byte[] seed) throws Exception {
        KeyGenerator kgen = KeyGenerator.getInstance("AES");
        SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
        sr.setSeed(seed);
        kgen.init(128,sr); // 192 and 256 bits may not be available
        SecretKey skey = kgen.generateKey();
        byte[] raw = skey.getEncoded();
        return raw;
    }


    private static byte[] encrypt(byte[] raw,byte[] clear) throws Exception {
        SecretKeySpec skeySpec = new SecretKeySpec(raw,"AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE,skeySpec);
        byte[] encrypted = cipher.doFinal(clear);
        return encrypted;
    }

    private static byte[] decrypt(byte[] raw,byte[] encrypted) throws Exception {
        SecretKeySpec skeySpec = new SecretKeySpec(raw,"AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE,skeySpec);
        byte[] decrypted = cipher.doFinal(encrypted);
        return decrypted;
    }

    public static String toHex(String txt) {
        return toHex(txt.getBytes());
    }
    public static String fromHex(String hex) {
        return new String(toByte(hex));
    }

    public static byte[] toByte(String hexString) {
        int len = hexString.length()/2;
        byte[] result = new byte[len];
        for (int i = 0; i < len; i++)
            result[i] = Integer.valueOf(hexString.substring(2*i,2*i+2),16).byteValue();
        return result;
    }

    public static String toHex(byte[] buf) {
        if (buf == null)
            return "";
        StringBuffer result = new StringBuffer(2*buf.length);
        for (int i = 0; i < buf.length; i++) {
            appendHex(result,buf[i]);
        }
        return result.toString();
    }
    private final static String HEX = "0123456789ABCDEF";
    private static void appendHex(StringBuffer sb,byte b) {
        sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
    }

}

解决方法

如果你看看 specification section 5,那么你可以看到输入,输出和状态都是128位.唯一不同的是键的大小：128,196或256位.因此加密16字节输入状态将产生16字节的输出状态.

你确定你不是用十六进制符号或类似的长度混合吗？如果是十六进制符号,那么它是正确的,因为每个字节需要两个字符来表示它：00-FF(范围0-255).

验证加密是否正确的另一种方法是通过进行等效解密,查看是否匹配明文输入字符串.

无论如何,它是正确的事情.这是一个测试：

public static void main(String[] args) {
  try {
    String plaintext = "Hello world",key = "test";
    String ciphertext = encrypt(key,plaintext);
    String plaintext2 = decrypt(key,ciphertext);
    System.out.println("Encrypting '" + plaintext +
                       "' yields: (" + ciphertext.length() + ") " + ciphertext);
    System.out.println("Decrypting it yields: " + plaintext2);
  }
  catch (Exception ex) {
      ex.printStackTrace();
  }
}

其中产生：

Encrypting ‘Hello world’ yields: (32)
5B68978D821FCA6022D4B90081F76B4F

Decrypting it yields: Hello world

（编辑：李大同）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!