Question

我正在编写一个代码，用于将加密文件从客户端发送到服务器但首先客户端将文件的加密消息摘要发送到服务器，然后发送文件的名称，最后它将发送加密文件的字节，但在服务器端，它将所有这些变量读作一个变量，即摘要，

当服务器尝试解密摘要时，它会抛出Illegal Block Size Exception 我的问题是服务器如何读取并将它们保存在不同的变量中？

客户

            // set mode to encrypt
            AesCipher.init(Cipher.ENCRYPT_MODE, key);

            DataOutputStream toServer = new DataOutputStream(socket.getOutputStream());

            // get the digest of the file
            MessageDigest md = MessageDigest.getInstance("MD5");
            byte[] hash = md.digest(bytes);

            // encrypt digest and write it to file
            byte [] encryptedHash = AesCipher.doFinal(hash);
            toServer.write(encryptedHash);


            // write file name to server
            toServer.writeUTF(fileName);

            //encrypt file
            byte[] encryptedByte = AesCipher.doFinal(bytes);


            // write file to server
            toServer.write(encryptedByte);
            toServer.flush();
            socket.close();

服务器

// read digest of the file
        byte [] digest =IOUtils.toByteArray(fromClient);

        // decrypt it
        AesCipher.init(Cipher.DECRYPT_MODE, key);
        byte[] decryptedDigest = AesCipher.doFinal(digest);

        // read file name to be received
        String fileName = fromClient.readUTF();

        File file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), fileName);
        file.createNewFile();
        FileOutputStream fos = new FileOutputStream(file);
        BufferedOutputStream bos = new BufferedOutputStream(fos);

        // read file bytes from client
        byte[] fileBytes = IOUtils.toByteArray(fromClient);

        AesCipher.init(Cipher.DECRYPT_MODE, key);
        byte[] decryptedByte = AesCipher.doFinal(fileBytes);
        bos.write(decryptedByte, 0, decryptedByte.length);
        bos.close();

我也试过这段代码，但它也没有用呢

// read digest of the file
         ByteArrayOutputStream buffer = new ByteArrayOutputStream();

        int nRead;
        byte[] data = new byte[1024];

        while ((nRead = fromClient.read(data, 0, data.length)) != -1) {
            buffer.write(data, 0, nRead);
        }

        buffer.flush();
        byte[] digest = buffer.toByteArray();

        // decrypt it
        AesCipher.init(Cipher.DECRYPT_MODE, key);
        byte[] decryptedDigest = AesCipher.doFinal(digest);

        // read file name to be received
        String fileName = fromClient.readUTF();

        File file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), fileName);
        file.createNewFile();
        FileOutputStream fos = new FileOutputStream(file);
        BufferedOutputStream bos = new BufferedOutputStream(fos);

        // read file bytes from client
        byte[] fileBytes = IOUtils.toByteArray(fromClient);

        AesCipher.init(Cipher.DECRYPT_MODE, key);
        byte[] decryptedByte = AesCipher.doFinal(fileBytes);
        bos.write(decryptedByte, 0, decryptedByte.length);
        bos.close();

Answer 1

IOUtils.toByteArray(InputStream)读取整个流。因此，不是只获取哈希字节，而是获得整个流，并且没有任何内容用于文件名或密文，并且哈希没有检查。

您不需要外部库。您可以使用DataInputStream和DataOutputStream完成所有操作。但是你确实需要在散列之前发送散列的长度。

客户端：

        // set mode to encrypt
        AesCipher.init(Cipher.ENCRYPT_MODE, key);

        DataOutputStream toServer = new DataOutputStream(socket.getOutputStream());

        // get the digest of the file
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] hash = md.digest(bytes);

        // encrypt digest and write it to file
        byte [] encryptedHash = AesCipher.doFinal(hash);
        toServer.writeInt(encryptedHash.length);
        toServer.write(encryptedHash);

        // write file name to server
        toServer.writeUTF(fileName);

        //encrypt file
        byte[] encryptedByte = AesCipher.doFinal(bytes);

        // write file to server
        toServer.writeInt(encryptedByte.length);
        toServer.write(encryptedByte);
        socket.close();

服务器：

    // read digest of the file
    int digestLength = fromClient.readInt();
    byte[] digest = new byte[digestLength];
    fromClient.readFully(digest);

    // decrypt it
    AesCipher.init(Cipher.DECRYPT_MODE, key);
    byte[] decryptedDigest = AesCipher.doFinal(digest);

    // read file name to be received
    String fileName = fromClient.readUTF();

    File file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), fileName);
    FileOutputStream fos = new FileOutputStream(file);
    BufferedOutputStream bos = new BufferedOutputStream(fos);

    // read file bytes from client
    int fileLength = fromClient.readInt();
    byte[] fileBytes = new byte[fileLength];
    fromClient.readFully(fileBytes);

    AesCipher.init(Cipher.DECRYPT_MODE, key);
    byte[] decryptedByte = AesCipher.doFinal(fileBytes);
    bos.write(decryptedByte, 0, decryptedByte.length);
    bos.close();

然而，使用CipherInputStream和CipherOutputStream可以更好地完成加密和解密部分。您不应将整个文件加载到内存中。

请注意，file.createNewFile()之前new FileOutputStream(...)来电是多余的。

为什么加密消息摘要是另一个谜。您应该将其用作最后一步，以便在解密后与本地生成的摘要进行比较。

从InputStream JAVA读取不同的输入

1 个答案: