如何使用Bouncy Castle Crypto API来加密和解密数据

Bouncy Castle Crypto API 是用JAVA编写的一套轻量级的加密API.同时，它也包括一个支持J2ME的版本．本例将介绍如何使用Bouncy Castle Crypto API来加密和解密数据

下边的Encryptor类允许你使用encryptString and decryptString方法加密和解密任意的数据:

import org.bouncycastle.crypto.*;
import org.bouncycastle.crypto.engines.*;
import org.bouncycastle.crypto.modes.*;
import org.bouncycastle.crypto.params.*;

// 一个简单的例子说明了如何使用Bouncy Castle
// 加密API来执行对任意数据的DES加密

public class Encryptor {

private BufferedBlockCipher cipher;
private KeyParameter key;

// 初始化加密引擎.
// 数组key的长度至少应该是8个字节.

public Encryptor( byte[] key ){
/*
cipher = new PaddedBlockCipher(
new CBCBlockCipher(
new DESEngine() ) );
*/

cipher = new PaddedBlockCipher(
new CBCBlockCipher(
new BlowfishEngine() ) );

this.key = new KeyParameter( key );
}

// 初始化加密引擎.
// 字符串key的长度至少应该是8个字节.

public Encryptor( String key ){
this( key.getBytes() );
}

// 做加密解密的具体工作

private byte[] callCipher( byte[] data )
throws CryptoException {
int size =
cipher.getOutputSize( data.length );
byte[] result = new byte[ size ];
int olen = cipher.processBytes( data, 0,
data.length, result, 0 );
olen += cipher.doFinal( result, olen );

if( olen < size ){
byte[] tmp = new byte[ olen ];
System.arraycopy(
result, 0, tmp, 0, olen );
result = tmp;
}

return result;
}

// 加密任意的字节数组，以字节数组的方式返回被加密的数据

public synchronized byte[] encrypt( byte[] data )
throws CryptoException {
if( data == null || data.length == 0 ){
return new byte[0];
}

cipher.init( true, key );
return callCipher( data );
}

// 加密一个字符串

public byte[] encryptString( String data )
throws CryptoException {
if( data == null || data.length() == 0 ){
return new byte[0];
}

return encrypt( data.getBytes() );
}

// 解密一个字节数组

public synchronized byte[] decrypt( byte[] data )
throws CryptoException {
if( data == null || data.length == 0 ){
return new byte[0];
}

cipher.init( false, key );
return callCipher( data );
}

// 解密一个字符串

public String decryptString( byte[] data )
throws CryptoException {
if( data == null || data.length == 0 ){
return "";
}

return new String( decrypt( data ) );
}
}

下边的代码演示如何使用上边的Encryptor类来加密解密数据

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.rms.*;

import org.bouncycastle.crypto.*;

import java.math.BigInteger;

public class CryptoTest extends MIDlet {

private Display display;
private Command exitCommand = new Command( "Exit", Command.EXIT, 1 );
private Command okCommand = new Command( "OK", Command.OK, 1 );

private Encryptor encryptor;
private RecordStore rs;

/** 构造函数*/
public CryptoTest() {
}

private void initialize() {
}

public void startApp() {
initialize();
if( display == null ){ // first time called...
initMIDlet();
}
}

public void pauseApp() {
}

public void destroyApp(boolean unconditional) {
exitMIDlet();
}

private void initMIDlet(){
display = Display.getDisplay( this );

// 打开名为"test3"的RecordStore
try {
rs = RecordStore.openRecordStore( "test3",
true );
} catch( RecordStoreException e ){
}

display.setCurrent( new AskForKey() );
}

public void exitMIDlet(){
try {
if( rs != null ){
rs.closeRecordStore();
}
} catch( RecordStoreException e ){
}

notifyDestroyed();
}

private void displayException( Exception e ){
Alert a = new Alert( "Exception" );
a.setString( e.toString() );
a.setTimeout( Alert.FOREVER );
display.setCurrent( a, new AskForKey() );
}

class AskForKey extends TextBox
implements CommandListener {
public AskForKey(){
super( "Enter a secret key:", "", 8, 0 );
setCommandListener( this );
addCommand( okCommand );
addCommand( exitCommand );
}

public void commandAction( Command c,
Displayable d ){
if( c == exitCommand ){
exitMIDlet();
}

String key = getString();
if( key.length() < 8 ){
Alert a = new Alert( "Key too short" );
a.setString( "The key must be " +
"8 characters long" );
setString( "" );
display.setCurrent( a, this );
return;
}

encryptor = new Encryptor( key );

try {
if( rs.getNextRecordID() == 1 ){
display.setCurrent(
new EnterMessage() );
} else {
byte[] data = rs.getRecord( 1 );
String str =
encryptor.decryptString( data );

Alert a =
new Alert( "Decryption" );
a.setTimeout( Alert.FOREVER );
a.setString(
"The decrypted string is '" +
str + "'" );
display.setCurrent( a, this );
}
} catch( RecordStoreException e ){
displayException( e );
} catch( CryptoException e ){
displayException( e );
}
}
}

class EnterMessage extends TextBox
implements CommandListener {
public EnterMessage(){


super( "Enter a message to encrypt:", "",
100, 0 );

BigInteger bigInt = new BigInteger("199999");

setCommandListener( this );
addCommand( okCommand );
}

public void commandAction( Command c,
Displayable d ){
String msg = getString();

try {
byte[] data =
encryptor.encryptString( msg );
rs.addRecord( data, 0, data.length );
} catch( RecordStoreException e ){
displayException( e );
} catch( CryptoException e ){
displayException( e );
}

display.setCurrent( new AskForKey() );
}
}

}

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/the3gwireless/archive/2006/04/24/674500.aspx