encrydecry.java

我在字符串加密时的处理是每次取字符串的三个字节

我在字符串加密时的处理是每次取字符串的三个字节，再把三个字符连成一个24位的整型，前8位存放第一个字符，中间8位存放第二个字符，最后8位存放第三个字符。再取这个整型数的前6位对应的数值去差用户提供对应表，转化成相应的字符，再取第二个6位，第三个6位，第四个六位进行字符的转换。再重复前面相同的操作值到整个字符串转换完毕。在解密的过程就是根据用户提供的表进行查找和移位换原字符串。
这种算法比通常的直接根据用户提供的表进行转换有更高的安全性，且加密解密的效率很高。
具体的代码如下：
          private static byte[] cvtTable = {
        (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)';'
    };
    static String encode(String content) {
        byte input[] = (content).getBytes();
        byte[] output;
        //System.out.println("input[] length = "+input.length);
        if(input.length%3 == 0) {
            //System.out.println("xxxxx");
            output = new byte[input.length/3*4];
        }
        else 
            output = new byte[((input.length / 3) + 1) * 4];
        int ridx = 0;
        int chunk = 0;

        for (int i = 0; i < input.length; i += 3) {
            int left = input.length - i;
            if (left > 2) {
                chunk = (input[i] << 16)|
                        (input[i + 1] << 8) |
                         input[i + 2];
                output[ridx++] = cvtTable[(chunk&0xFC0000)>>18];
                output[ridx++] = cvtTable[(chunk&0x3F000) >>12];
                output[ridx++] = cvtTable[(chunk&0xFC0)   >> 6];
                output[ridx++] = cvtTable[(chunk&0x3F)];
            } else if (left == 2) {
                chunk = (input[i] << 16) |
                        (input[i + 1] << 8);
                output[ridx++] = cvtTable[(chunk&0xFC0000)>>18];
                output[ridx++] = cvtTable[(chunk&0x3F000) >>12];
                output[ridx++] = cvtTable[(chunk&0xFC0)   >> 6];
                output[ridx++] = cvtTable[63];
            } else if(left == 1){
                chunk = input[i] << 16;
                output[ridx++] = cvtTable[(chunk&0xFC0000)>>18];
                output[ridx++] = cvtTable[(chunk&0x3F000) >>12];
                output[ridx++] = cvtTable[63];
                output[ridx++] = cvtTable[63];
            }
        }
        return new String(output);
    }
          static String revert(String content) {
        byte tempArray[] = (content).getBytes();
        byte[] result = new byte[tempArray.length/4*3];
        int temp = 0;
        int pos = 0;

        //for(int i= tempArray.length-1;i>= 0;i--)
           //System.out.println(tempArray[i]);
        
        for(int i = 0;i < tempArray.length;i += 4) {

            temp = (search(tempArray[i]) << 18) | 
                   (search(tempArray[i+1]) << 12) |
                   (search(tempArray[i+2]) << 6) |
                   (search(tempArray[i+3]));
            
            result[pos++] = (byte)((temp & 0xff0000) >> 16);
            result[pos++] = (byte)((temp & 0xff00) >> 8);
            result[pos++] = (byte)(temp & 0xff);
        }
        return new String(result);
    }
    static int search(int target) {
        int  i = 0;
        while(target != cvtTable[i] && i < 64) {
            i++;
        }
        return i;
    }