我正在做一个简单的加密文件传输系统，现在因运行时异常而停止：
Exception in thread "main" javax.crypto.BadPaddingException: Given final block not properly padded
at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:811)
at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:676)
at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:313)
at javax.crypto.Cipher.doFinal(Cipher.java:2087)
at ftpclient.FTPClient.main(FTPClient.java:82)
我尝试使用字符串调试我的代码，使用相同的密钥进行加密和解密，然后才能正常工作。但是，当我尝试从文件传输流时，总会出现此异常。
以下是双方的代码。首先，他们将通过RSA交换对称密钥（AES密钥），然后通过AES加密传输大文件。我们可以关注每个代码的最后部分，其中文件是通过AES密钥加密和解密的。
服务器端：
package ftpserver;
import java.io.*;
import java.net.*;
import javax.crypto.*;
import java.security.*;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base64;
/**
*
* @author Han
*/
public class FTPServer {
public static void main(String[] args) throws Exception {
//generate symmetric key and initialize cipher for AES
SecretKey skey = null;
Cipher aes = Cipher.getInstance("AES/ECB/PKCS5Padding");
KeyGenerator kg = KeyGenerator.getInstance("AES");
kg.init(128);
skey = kg.generateKey();
//get public key of the receive side
final String PUBLIC_KEY_PATH = "key_b.public";
PublicKey publickey = null;
try {
FileInputStream fis;
fis = new FileInputStream(PUBLIC_KEY_PATH);
ObjectInputStream oin = new ObjectInputStream(fis);
publickey = (PublicKey) oin.readObject();
oin.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
};
//encrypte symmetric key with own private key and send out
Cipher rsa = Cipher.getInstance("RSA");
rsa.init(Cipher.ENCRYPT_MODE, publickey);
byte cipherSKey[] = rsa.doFinal(skey.getEncoded());
//System.out.println(skey); //debug
//create tcp server socket
ServerSocket tcp = new ServerSocket(2000);
Socket client = tcp.accept();
//get input&output stream from the TCP connection
InputStream in = client.getInputStream();
OutputStream out = client.getOutputStream();
//generate a file input stream to get stream from file
File sentFile = new File("F:\\test.txt");
FileInputStream fin = new FileInputStream(sentFile);
//send encrypted symmetric key first
out.write("Symmetric Key:\r\n".getBytes());
out.write(cipherSKey);
DataInputStream din = new DataInputStream(in);
while(true)
{
if(din.readLine().equals("Received."))
{
System.out.println("Send key successfully.");
break;
}
};
//send files
int count;
byte[] bytearray = new byte[8192];
byte[] cipherbuffer;
while((count = fin.read(bytearray))>0)
{
cipherbuffer = Base64.encodeBase64(aes.doFinal(bytearray));
out.write(cipherbuffer,0,cipherbuffer.length);
System.out.println(count+" bytes have been sent.");
};
out.flush();
out.close();
client.close();
}
}
客户端：
package ftpclient;
import java.io.*;
import java.net.*;
import java.security.PrivateKey;
import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base64;
/**
*
* @author Han
*/
public class FTPClient {
public static void main(String[] args) throws Exception
{
//get the private key of this side
final String PUBLIC_KEY_PATH = "key_b.privat";
PrivateKey privatkey = null;
try {
FileInputStream fis;
fis = new FileInputStream(PUBLIC_KEY_PATH);
ObjectInputStream oin = new ObjectInputStream(fis);
privatkey = (PrivateKey) oin.readObject();
oin.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
};
Cipher rsa = Cipher.getInstance("RSA");
rsa.init(Cipher.DECRYPT_MODE, privatkey);
//create tcp client socket
Socket tcp = new Socket("192.168.1.185",2000);
InputStream in = tcp.getInputStream();
OutputStream out = tcp.getOutputStream();
DataInputStream din = new DataInputStream(in);
//receive symmetric key from server
byte keybuffer[] = new byte[128];
SecretKey skey = null;
while(true)
{
if(din.readLine().equals("Symmetric Key:"))
{
System.out.println("Start to receiving key...");
in.read(keybuffer);
byte[] skeycode = rsa.doFinal(keybuffer);
skey = new SecretKeySpec(skeycode, 0, skeycode.length, "AES");
out.write("Received.\r\n".getBytes());
break;
}
};
//create cipher for symmetric decryption
Cipher aes = Cipher.getInstance("AES/ECB/PKCS5Padding");
aes.init(Cipher.DECRYPT_MODE, skey);
//System.out.println(skey); //debug
//create file stream
FileOutputStream fos = new FileOutputStream("E:\\test_cp.txt");
int count;
int i = 0;
byte[] bytearray = new byte[8192];
byte[] buffer;
while((count = in.read(bytearray)) > 0)
{
buffer = (aes.doFinal(Base64.decodeBase64(bytearray)));
fos.write(buffer,0,buffer.length);
i +=count;
System.out.println(i+" bytes have been received.");
};
fos.flush();
fos.close();
in.close();
tcp.close();
System.out.println("File Transfer completed");
}
}
答案 0 :(得分：3)
您多次致电doFinal。或至少试图。
当您读取数据时，并非所有数据都会到达或立即被读入缓冲区。所以你解密一些，然后再读一遍。一切都好。
但是当你这样做时，你每次都在调用doFinal，而不是update。这是错误的，是错误的原因。相反，将doFinal替换为update，然后在读完所有数据后添加额外的doFinal（正好有doFinal()不带参数）。
请参阅http://docs.oracle.com/javase/7/docs/api/javax/crypto/Cipher.html
另见http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_codebook_.28ECB.29为什么ecb模式通常不是一个好主意（看看企鹅图片）。