关于RSA分段加密和解密的问题

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由于RSA不能加密数据太长的问题，采用了分段加密，单是用了加密之后，明文由原来的4个字节变成了256个字节，解密后变成了512个字节，新人刚接触RSA不懂这方面的问题特来请教一下。下面上我的加密和解密以及测试代码
加密：

/**
	 * 加密。注意密钥是可以获取到它适用的算法的。
	 * 
	 * @param plainText
	 * @param privateKey
	 * @return
	 */
	public static byte[] encrypt(PrivateKey privateKey, byte[] data) {
          try {
			Cipher cipher=Cipher.getInstance("RSA/ECB/NoPadding");
               cipher.init(Cipher.ENCRYPT_MODE, privateKey);
               
               //数据长度
               int inputLen=data.length;
               ByteArrayOutputStream baos=new ByteArrayOutputStream();
               //
               int offSet=0;
               byte[] cache;
               int i=0;
               while(inputLen-offSet>0){
            	   if(inputLen-offSet>117){
            		   cache=cipher.doFinal(data, offSet, 117);
            	   }else{
            		  cache=cipher.doFinal(data, offSet, inputLen-offSet);
            	   }
            	   baos.write(cache,0,cache.length);
            	   i++;
            	   offSet=i*117;
               }
               byte[] encryptedData=baos.toByteArray();
               baos.close();
               return encryptedData;
		} catch (NoSuchAlgorithmException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchPaddingException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InvalidKeyException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalBlockSizeException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (BadPaddingException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		return null;
	}

解密：

/**
	 * 解密
	 * 
	 * @param encodedText
	 * @param publicKey
	 * @return
	 */
	public static byte[] decode(byte[] encodedText, PublicKey publicKey) {
	   try {
		Cipher cipher=Cipher.getInstance("RSA/ECB/NoPadding");
		cipher.init(Cipher.DECRYPT_MODE, publicKey);
		int inputLen=encodedText.length;
		ByteArrayOutputStream baos=new ByteArrayOutputStream();
		int offSet=0;
		byte[] cache;
		int i=0;
		while(inputLen-offSet>0){
			if(inputLen-offSet>128){
				cache=cipher.doFinal(encodedText, offSet, 128);
			}else{
				cache=cipher.doFinal(encodedText, offSet, inputLen-offSet);
			}
			baos.write(cache, 0, cache.length);
			i++;
			offSet=i*128;
		}
		byte[] decryptedData=baos.toByteArray();
		baos.close();
		return decryptedData;
	} catch (NoSuchAlgorithmException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} catch (NoSuchPaddingException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} catch (InvalidKeyException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} catch (IllegalBlockSizeException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} catch (BadPaddingException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} catch (IOException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}
	   return null;
	}

测试代码

public class Test {
	// 密钥库密码
		private static final String STORE_PASS = "Changeme123";

		// 证书别名
		private static final String ALIAS = "myCertificate";

		// 服务器本地数字证书
		private static final String KEYSTORE_PATH = "C:\\Users\\Administrator\\myKeystore.keystore";
	
		// 数字证书（需要发送给客户端）
		private static final String CERT_PATH = "C:\\Users\\Administrator\\myCer.cer";

		// JDK6只支持X.509标准的证书
		private static final String CERT_TYPE = "X.509";
	
    public static void main(String[] args) throws Exception {
    	KeyStore keyStore = ServerCertificateUtil.getKeyStore(STORE_PASS,
    			KEYSTORE_PATH);

    	// 获取私钥
    	PrivateKey privateKey = ServerCertificateUtil.getPrivateKey(keyStore, ALIAS,
    			STORE_PASS);

    	// 获取证书
    	X509Certificate certificate = ServerCertificateUtil.getCertificateByKeystore(
    			keyStore, ALIAS);
    	 	
    	X509Certificate receivedCertificate = ClientCertificateUtil.getCertificateByCertPath(
				CERT_PATH, CERT_TYPE);
		
    	PublicKey publicKey = ClientCertificateUtil.getPublicKey(receivedCertificate);
    	
    	byte[] bb={12,21,14,16};
		byte[] bb1=ServerCertificateUtil.encrypt(privateKey, bb);
		byte[] bb2=ClientCertificateUtil.decode(bb1, publicKey);
System.out.println("bb1的长度"+bb1.length);		
System.out.println("bb1的长度"+bb2.length);	
		for(int i=0;i<bb2.length;i++){
			System.out.println(bb2[i]);
		}
	}
	
}

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