android aes加密

如下代码中在生成密钥的时候，基于password , 这里的SequreRandom ,以password设置了种子后，便会产生同等序列的随机值，因此解密方知道password 便可以解密，当然也得基于同等的SequereRandom. 但是android 把此类的SequreRandom 4.2 后做了修改，因为有可预测破解的风险，所以此类实现方式，太依赖于系统实现，已经不可取了。况且此类方式，产生固定不变的密文，容易破解。

详细情况参考文档，解释了问题，以及提出了相关的方案。

http://www.tuicool.com/articles/Zn6ZFny

http://netsecurity.51cto.com/art/201304/389999.htm

package widget;

import java.security.SecureRandom;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

/**
 * @author carlos [email protected]
 * @version 创建时间：2012-5-17 上午9:48:35 类说明
 */

public class AESUtils {
    public static final String TAG = "AESUtils";

    public static String encrypt(String key, String src) throws Exception {     
        byte[] rawKey = getRawKey(key.getBytes());     
        byte[] result = encrypt(rawKey, src.getBytes());     
        return toHex(result);     
    }     
         
    public static String decrypt(String key, String encrypted) throws Exception {     
        byte[] rawKey = getRawKey(key.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");   
        // SHA1PRNG 强随机种子算法, 要区别4.2以上版本的调用方法  
         SecureRandom sr = null;  
       if (android.os.Build.VERSION.SDK_INT >=  17) {  
         sr = SecureRandom.getInstance("SHA1PRNG", "Crypto");  
       } else {  
         sr = SecureRandom.getInstance("SHA1PRNG");  
       }   
        sr.setSeed(seed);     
        kgen.init(256, sr); //256 bits or 128 bits,192bits  
        SecretKey skey = kgen.generateKey();     
        byte[] raw = skey.getEncoded();     
        return raw;     
    }     
    
         
    private static byte[] encrypt(byte[] key, byte[] src) throws Exception {     
        SecretKeySpec skeySpec = new SecretKeySpec(key, "AES");     
        Cipher cipher = Cipher.getInstance("AES");     
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);     
        byte[] encrypted = cipher.doFinal(src);     
        return encrypted;     
    }     
    
    private static byte[] decrypt(byte[] key, byte[] encrypted) throws Exception {     
        SecretKeySpec skeySpec = new SecretKeySpec(key, "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));     
    }     
}

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