java安全技术-Base64编码与解码

BASE64编码入门

l         概念及原理介绍

Base64采用了一种很简单的编码转换：对于待编码数据，以3个字节为单位，依次取6位数据并在前面补上两个0形成新的8位编码，由于3*8=4*6，这样3个字节的输入会变成4个字节的输出，长度上增加了1/3。

Base64编码表

Value Encoding Value Encoding Value Encoding Value Encoding

0 A 17 R 34 i 51 z

1 B 18 S 35 j 52 0

2 C 19 T 36 k 53 1

3 D 20 U 37 l 54 2

4 E 21 V 38 m55 3

5 F 22 W39 n56 4

6 G 23 X 40 o 57 5

7 H 24 Y 41 p 58 6

8 I 25 Z 42 q 59 7

9 J 26 a 43 r 60 8

10 K 27 b 44 s 61 9

11 L 28 c 45 t 62 +

12 M 29 d46 u 63 /

13 N 30 e47 v

14 O 31 f 48 w (pad) =

15 P 32 g49 x

16 Q 33 h50 y

说实话不知道怎么用，放在这里备用。

l         Java的实现。

1.         这种是通过比较原始的方法实现的，但是可以作为一个工具类供以后使用。

/**  
 *base64需要引用别的jar需要下载的。这里是源码改变的一个类，也能实现功能  
 */ 
package com.lzz.security;  
 
public class Base64 {  
    private static final byte[] encodingTable = {  
            (byte) "A", (byte) "B", (byte) "C", (byte) "D", (byte) "E",  
            (byte) "F", (byte) "G", (byte) "H", (byte) "I", (byte) "J",  
            (byte) "K", (byte) "L", (byte) "M", (byte) "N", (byte) "O",  
            (byte) "P", (byte) "Q", (byte) "R", (byte) "S", (byte) "T",  
            (byte) "U", (byte) "V", (byte) "W", (byte) "X", (byte) "Y",  
            (byte) "Z", (byte) "a", (byte) "b", (byte) "c", (byte) "d",  
            (byte) "e", (byte) "f", (byte) "g", (byte) "h", (byte) "i",  
            (byte) "j", (byte) "k", (byte) "l", (byte) "m", (byte) "n",  
            (byte) "o", (byte) "p", (byte) "q", (byte) "r", (byte) "s",  
            (byte) "t", (byte) "u", (byte) "v", (byte) "w", (byte) "x",  
            (byte) "y", (byte) "z", (byte) "0", (byte) "1", (byte) "2",  
            (byte) "3", (byte) "4", (byte) "5", (byte) "6", (byte) "7",  
            (byte) "8", (byte) "9", (byte) "+", (byte) "/" 
        };  
    private static final byte[] decodingTable;  
      
    static {  
        decodingTable = new byte[128];  
        for (int i = 0; i < 128; i++) {  
            decodingTable[i] = (byte) -1;  
        }  
        for (int i = "A"; i <= "Z"; i++) {  
            decodingTable[i] = (byte) (i - "A");  
        }  
        for (int i = "a"; i <= "z"; i++) {  
            decodingTable[i] = (byte) (i - "a" + 26);  
        }  
        for (int i = "0"; i <= "9"; i++) {  
            decodingTable[i] = (byte) (i - "0" + 52);  
        }  
        decodingTable["+"] = 62;  
        decodingTable["/"] = 63;  
    }  
      
      
    /**  
     * 编码函数，通过编码规则把传入的  
     * @param data  
     * @return  
     */ 
    public static String encode(String s) {  
        String encodeStr;  
        byte[] data=s.getBytes();   
        byte[] bytes;  
        int modulus = data.length % 3;  
        if (modulus == 0) {  
            bytes = new byte[(4 * data.length) / 3];  
        } else {  
            bytes = new byte[4 * ((data.length / 3) + 1)];  
        }  
        int dataLength = (data.length - modulus);  
        int a1;  
        int a2;  
        int a3;  
        for (int i = 0, j = 0; i < dataLength; i += 3, j += 4) {  
            a1 = data[i] & 0xff;  
            a2 = data[i + 1] & 0xff;  
            a3 = data[i + 2] & 0xff;  
            bytes[j] = encodingTable[(a1 >>> 2) & 0x3f];  
            bytes[j + 1] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f];  
            bytes[j + 2] = encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f];  
            bytes[j + 3] = encodingTable[a3 & 0x3f];  
        }  
        int b1;  
        int b2;  
        int b3;  
        int d1;  
        int d2;  
        switch (modulus) {  
        case 0: /* nothing left to do */ 
            break;  
        case 1:  
            d1 = data[data.length - 1] & 0xff;  
            b1 = (d1 >>> 2) & 0x3f;  
            b2 = (d1 << 4) & 0x3f;  
            bytes[bytes.length - 4] = encodingTable[b1];  
            bytes[bytes.length - 3] = encodingTable[b2];  
            bytes[bytes.length - 2] = (byte) "=";  
            bytes[bytes.length - 1] = (byte) "=";  
            break;  
        case 2:  
            d1 = data[data.length - 2] & 0xff;  
            d2 = data[data.length - 1] & 0xff;  
            b1 = (d1 >>> 2) & 0x3f;  
            b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;  
            b3 = (d2 << 2) & 0x3f;  
            bytes[bytes.length - 4] = encodingTable[b1];  
            bytes[bytes.length - 3] = encodingTable[b2];  
            bytes[bytes.length - 2] = encodingTable[b3];  
            bytes[bytes.length - 1] = (byte) "=";  
            break;  
        }  
        encodeStr= new String(bytes);  
        return encodeStr;  
    }  
      
    public static byte[] decode(byte[] data) {  
        byte[] bytes;  
        byte b1;  
        byte b2;  
        byte b3;  
        byte b4;  
        data = discardNonBase64Bytes(data);  
        if (data[data.length - 2] == "=") {  
            bytes = new byte[(((data.length / 4) - 1) * 3) + 1];  
        } else if (data[data.length - 1] == "=") {  
            bytes = new byte[(((data.length / 4) - 1) * 3) + 2];  
        } else {  
            bytes = new byte[((data.length / 4) * 3)];  
        }  
        for (int i = 0, j = 0; i < (data.length - 4); i += 4, j += 3) {  
            b1 = decodingTable[data[i]];  
            b2 = decodingTable[data[i + 1]];  
            b3 = decodingTable[data[i + 2]];  
            b4 = decodingTable[data[i + 3]];  
            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));  
            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));  
            bytes[j + 2] = (byte) ((b3 << 6) | b4);  
        }  
        if (data[data.length - 2] == "=") {  
            b1 = decodingTable[data[data.length - 4]];  
            b2 = decodingTable[data[data.length - 3]];  
            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));  
        } else if (data[data.length - 1] == "=") {  
            b1 = decodingTable[data[data.length - 4]];  
            b2 = decodingTable[data[data.length - 3]];  
            b3 = decodingTable[data[data.length - 2]];  
            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));  
            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));  
        } else {  
            b1 = decodingTable[data[data.length - 4]];  
            b2 = decodingTable[data[data.length - 3]];  
            b3 = decodingTable[data[data.length - 2]];  
            b4 = decodingTable[data[data.length - 1]];  
            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));  
            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));  
            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);  
        }  
        return bytes;  
    }  
      
    /**  
     * 解码方法  
     * @param  String  
     * @return String  
     */ 
    public static String decode(String data) {  
        String decodeStr;  
        byte[] bytes;  
        byte b1;  
        byte b2;  
        byte b3;  
        byte b4;  
        data = discardNonBase64Chars(data);  
        if (data.charAt(data.length() - 2) == "=") {  
            bytes = new byte[(((data.length() / 4) - 1) * 3) + 1];  
        } else if (data.charAt(data.length() - 1) == "=") {  
            bytes = new byte[(((data.length() / 4) - 1) * 3) + 2];  
        } else {  
            bytes = new byte[((data.length() / 4) * 3)];  
        }  
        for (int i = 0, j = 0; i < (data.length() - 4); i += 4, j += 3) {  
            b1 = decodingTable[data.charAt(i)];  
            b2 = decodingTable[data.charAt(i + 1)];  
            b3 = decodingTable[data.charAt(i + 2)];  
            b4 = decodingTable[data.charAt(i + 3)];  
            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));  
            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));  
            bytes[j + 2] = (byte) ((b3 << 6) | b4);  
        }  
        if (data.charAt(data.length() - 2) == "=") {  
            b1 = decodingTable[data.charAt(data.length() - 4)];  
            b2 = decodingTable[data.charAt(data.length() - 3)];  
            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));  
        } else if (data.charAt(data.length() - 1) == "=") {  
            b1 = decodingTable[data.charAt(data.length() - 4)];  
            b2 = decodingTable[data.charAt(data.length() - 3)];  
            b3 = decodingTable[data.charAt(data.length() - 2)];  
            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));  
            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));  
        } else {  
            b1 = decodingTable[data.charAt(data.length() - 4)];  
            b2 = decodingTable[data.charAt(data.length() - 3)];  
            b3 = decodingTable[data.charAt(data.length() - 2)];  
            b4 = decodingTable[data.charAt(data.length() - 1)];  
            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));  
            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));  
            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);  
        }  
         
        decodeStr=new String(bytes);  
        return decodeStr;  
    }  
      
      
    private static byte[] discardNonBase64Bytes(byte[] data) {  
        byte[] temp = new byte[data.length];  
        int bytesCopied = 0;  
        for (int i = 0; i < data.length; i++) {  
            if (isValidBase64Byte(data[i])) {  
                temp[bytesCopied++] = data[i];  
            }  
        }  
        byte[] newData = new byte[bytesCopied];  
        System.arraycopy(temp, 0, newData, 0, bytesCopied);  
        return newData;  
    }  
      
      
    private static String discardNonBase64Chars(String data) {  
        StringBuffer sb = new StringBuffer();  
        int length = data.length();  
        for (int i = 0; i < length; i++) {  
            if (isValidBase64Byte((byte) (data.charAt(i)))) {  
                sb.append(data.charAt(i));  
            }  
        }  
        return sb.toString();  
    }  
      
      
    private static boolean isValidBase64Byte(byte b) {  
        if (b == "=") {  
            return true;  
        } else if ((b < 0) || (b >= 128)) {  
            return false;  
        } else if (decodingTable[b] == -1) {  
            return false;  
        }  
        return true;  
    }  
      
    /**  
     * 用于测试的主函数  
     * @param args  
     */ 
    public static void main(String[] args) {  
        String data = "我爱上海东方明珠";  
        String encoderesult = Base64.encode(data);  
        String decoderesult = Base64.decode(encoderesult);  
        System.out.println("编码前："+data);  
        System.out.println("解码前："+encoderesult);  
        System.out.println("解码后："+decoderesult);  
    }  
      
} 

输出结果为：

编码前：我爱上海东方明珠

解码前：ztKwrsnPuqO2q7e9w/fW6Q==

解码后：我爱上海东方明珠

2        这种方法则是直接调用已经实现的jar的类就可以了

    /** 
* 这里是通过javaapi已经实现的类来实现base64编码的编码和解码过程  
*/ 
package com.lzz.security;  

import it.sauronsoftware.base64.Base64;  

public class MyBase64Ecoding {  
  
/**  
 * 加密,这里jar中提供的重载方法比较多，可以自己选择  
 */ 
public static String encryptBase64 (String key){  
    return new Base64().encode(key);  
}  
  
/**  
 * 解密  
 */ 
public static String decryptBase64(String key){  
    return new Base64().decode(key);  
}  

/**  
 * 主函数  
 * @param void  
 */ 
  
public static void main(String[] args) {  
    String data=new String("宇信易诚科技有限公司");  
    String endata=encryptBase64(data);  
    String dedata=decryptBase64(endata);  
    System.out.println("用于测试的字符串："+data);  
    System.out.println("加密之后的字符串："+endata);  
    System.out.println("解密之后的字符串："+dedata);  
}  

}  

jar包下载地址：http://down.51cto.com/data/483451

}

输入结果为：

用于测试的字符串：宇信易诚科技有限公司

加密之后的字符串：0+7QxdLXs8+/xry809DP3rmry74=

解密之后的字符串：宇信易诚科技有限公司