一个用java写的加解密程序.txt

一个用java写的加密解密程序

import java.io.*;       // needed only for main() method. 


/** 
*   Provides encoding of raw bytes to base64-encoded characters, and 
*  decoding of base64 characters to raw bytes. 
* 
* @author Kevin Kelley ([e-mail]) 
* @version 1.3 
* @date 06 August 1998 
* @modified 14 February 2000 
* @modified 22 September 2000 
*/ 
public class B64 { 

/** 
* returns an array of base64-encoded characters to represent the 
* passed data array. 
* 
* @param data the array of bytes to encode 
* @return base64-coded character array. 
*/ 
static public char[] encode(byte[] data) 
{ 
    char[] out = new char[((data.length + 2) / 3) * 4]; 
    System.out.println(data.length+" "+out.length+" "+((data.length + 2) / 3) * 4); 

    // 
    // 3 bytes encode to 4 chars.  Output is always an even 
    // multiple of 4 characters. 
    // 
    for (int i=0, index=0; i<data.length; i+=3, index+=4) { 
boolean quad = false; 
boolean trip = false; 

int val = (0xFF & (int) data[i]); 
val <<= 8; 
if ((i+1) < data.length) { 
val |= (0xFF & (int) data[i+1]); 
trip = true; 
} 
val <<= 8; 
if ((i+2) < data.length) { 
val |= (0xFF & (int) data[i+2]); 
quad = true; 
} 
out[index+3] = alphabet[(quad? (val & 0x3F): 64)]; 
val >>= 6; 
        out[index+2] = alphabet[(trip? (val & 0x3F): 64)]; 
        val >>= 6; 
        out[index+1] = alphabet[val & 0x3F]; 
        val >>= 6; 
        out[index+0] = alphabet[val & 0x3F]; 
    } 
    return out; 
} 

  /** 
   * Decodes a BASE-64 encoded stream to recover the original 
   * data. White space before and after will be trimmed away, 
   * but no other manipulation of the input will be performed. 
   * 
   * As of version 1.2 this method will properly handle input 
   * containing junk characters (newlines and the like) rather 
   * than throwing an error. It does this by pre-parsing the 
   * input and generating from that a count of VALID input 
   * characters. 
   **/ 
static public byte[] decode(char[] data) 
{ 
    // as our input could contain non-BASE64 data (newlines, 
    // whitespace of any sort, whatever) we must first adjust 
    // our count of USABLE data so that... 
    // (a) we don't misallocate the output array, and 
    // (b) think that we miscalculated our data length 
    //     just because of extraneous throw-away junk 

    int tempLen = data.length; 
    for( int ix=0; ix<data.length; ix++ ) 
{ 
if( (data[ix] > 255) || codes[ data[ix] ] < 0 ) 
--tempLen; // ignore non-valid chars and padding 
} 
// calculate required length: 
// -- 3 bytes for every 4 valid base64 chars 
// -- plus 2 bytes if there are 3 extra base64 chars, 
// or plus 1 byte if there are 2 extra. 

int len = (tempLen / 4) * 3; 
if ((tempLen % 4) == 3) len += 2; 
if ((tempLen % 4) == 2) len += 1; 

byte[] out = new byte[len]; 



int shift = 0; // # of excess bits stored in accum 
int accum = 0; // excess bits 
int index = 0; 

// we now go through the entire array (NOT using the 'tempLen' value) 
for (int ix=0; ix<data.length; ix++) 
{ 
int value = (data[ix]>255)? -1: codes[ data[ix] ]; 

        if ( value >= 0 )           // skip over non-code 
        { 
            accum <<= 6; // bits shift up by 6 each time thru 
shift += 6; // loop, with new bits being put in 
accum |= value; // at the bottom. 
if ( shift >= 8 )       // whenever there are 8 or more shifted in, 
            { 
                shift -= 8;         // write them out (from the top, leaving any 
                out[index++] =      // excess at the bottom for next iteration. 
                    (byte) ((accum >> shift) & 0xff); 
            } 
        } 
        // we will also have skipped processing a padding null byte ('=') here; 
        // these are used ONLY for padding to an even length and do not legally 
        // occur as encoded data. for this reason we can ignore the fact that 
        // no index++ operation occurs in that special case: the out[] array is 
        // initialized to all-zero bytes to start with and that works to our 
        // advantage in this combination. 
    } 

    // if there is STILL something wrong we just have to throw up now! 
    if( index != out.length) 
    { 
        throw new Error("Miscalculated data length (wrote " + index + " instead of " + out.length + ")"); 
    } 

    return out; 
} 


// 
// code characters for values 0..63 
// 
static private char[] alphabet = 
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=" 
        .toCharArray(); 

// 
// lookup table for converting base64 characters to value in range 0..63 
// 
static private byte[] codes = new byte[256]; 
static { 
    for (int i=0; i<256; i++) 
{ 
codes[i] = -1; 
System.out.print(i+"&"+codes[i]+" "); 
} 
for (int i = 'A'; i <= 'Z'; i++) 
{ 
codes[i] = (byte)( i - 'A'); 
System.out.print(i+"&"+codes[i]+" "); 
} 

for (int i = 'a'; i <= 'z'; i++) 
{ 
codes[i] = (byte)(26 + i - 'a'); 
System.out.print(i+"&"+codes[i]+" "); 
} 
for (int i = '0'; i <= '9'; i++) 
{ 
codes[i] = (byte)(52 + i - '0'); 
System.out.print(i+"&"+codes[i]+" "); 
} 
codes['+'] = 62; 
codes['/'] = 63; 
} 




/////////////////////////////////////////////////// 
// remainder (main method and helper functions) is 
// for testing purposes only, feel free to clip it. 
/////////////////////////////////////////////////// 

public static void doEncode(String filename) 
{ 

File file = new File(filename); 
if (!file.exists()) 
{ 
System.out.println("Error: file '" + filename + "' doesn't exist!"); 
System.exit(0); 
} 


else 
{ 
byte[] decoded = readBytes(file); 
char[] encoded = encode(decoded); 
writeChars(file, encoded); 
} 
} 

public static void doDecode(String filename) 
{ 

File file = new File(filename); 
if (!file.exists()) 
{ 
System.out.println("Error: file '" + filename + "' doesn't exist!"); 
System.exit(0); 
} 
else 
{ 
char[] encoded = readChars(file); 
byte[] decoded = decode(encoded); 
writeBytes(file, decoded); 
} 

} 





private static byte[] readBytes(File file) 
{ 
ByteArrayOutputStream baos = new ByteArrayOutputStream(); 
try 
{ 
InputStream fis = new FileInputStream(file); 
InputStream is = new BufferedInputStream(fis); 
int count = 0; 
byte[] buf = new byte[16384]; 
while ((count=is.read(buf)) != -1) { 
if (count > 0) baos.write(buf, 0, count); 
        } 
        is.close(); 
    } 
    catch (Exception e) { e.printStackTrace(); } 

    return baos.toByteArray(); 
} 

private static char[] readChars(File file) 
{ 
    CharArrayWriter caw = new CharArrayWriter(); 
    try 
    { 
        Reader fr = new FileReader(file); 
        Reader in = new BufferedReader(fr); 
        int count = 0; 
        char[] buf = new char[16384]; 
        while ((count=in.read(buf)) != -1) { 
            if (count > 0) caw.write(buf, 0, count); 
        } 
        in.close(); 
    } 
    catch (Exception e) { e.printStackTrace(); } 

    return caw.toCharArray(); 
} 

private static void writeBytes(File file, byte[] data) { 
    try { 
        OutputStream fos = new FileOutputStream(file); 
        OutputStream os = new BufferedOutputStream(fos); 
        os.write(data); 
        os.close(); 
    } 
    catch (Exception e) { e.printStackTrace(); } 
} 

private static void writeChars(File file, char[] data) { 
    try { 
        Writer fos = new FileWriter(file); 
        Writer os = new BufferedWriter(fos); 
        os.write(data); 
        os.close(); 
    } 
    catch (Exception e) { e.printStackTrace(); } 
} 
/////////////////////////////////////////////////// 
// end of test code. 
/////////////////////////////////////////////////// 

}