Question

我正在尝试使用包含在RSA密钥对中的AES密钥加密文件..

我正在尝试将包装好的密钥放在文件的开头，然后为了解密，我将包装密钥的前256个字节用于获取它。

问题是我正在以1024字节的块加密文件。因此，对于解密，我需要获取文件的最后一个字节（不是前256个，因为它们是关键）

所以在this image中你可以看到过程

<a href='http://postimg.org/image/htmelww63/' target='_blank'><img src='http://s1.postimg.org/htmelww63/Blank_Flowchart_New_Page.jpg' border='0' alt="Blank Flowchart New Page" /></a>

所以问题是当我需要解密除前256个字节之外的文件。我找不到一个有效的算法...

这里是加密代码：

public static void fileEncripWrapped(File in, File out, PublicKey pub, byte [] key) {  

    try {
        SecretKeySpec keySpec = new SecretKeySpec(key, "AES");

        //Encrypting wrapped key      
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.WRAP_MODE, pub);
        byte[] encKey = cipher.wrap(keySpec);

        FileOutputStream osAppend  = new FileOutputStream(out);

        osAppend.write(encKey);
        osAppend.close();


        // Crypting the file 
         cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
        cipher.init(Cipher.ENCRYPT_MODE, keySpec);

        FileInputStream is = new FileInputStream(in);
        CipherOutputStream os = new CipherOutputStream(new FileOutputStream(out, true), cipher);

        copy(is, os);

        is.close();
        os.close();

    } catch (Exception ex) {
        System.err.println("Ha succeït un error xifrant: " + ex);
    }
}

这是我用于将inputStream以1024字节为单位复制到outputStream的代码。

private static void copy(InputStream is, OutputStream os) throws IOException {
    int i;
    byte[] b = new byte[1024];
    while((i=is.read(b))!=-1) {
       os.write(b, 0, i);
    }
}

现在问题在于解密：

public static void fileUncryptWrapped(File in, File out, PrivateKey priv) { 

   try {

       Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
       cipher.init(Cipher.UNWRAP_MODE, priv);

       //First we must to take the wrapped key in the first 256 bytes of the file: 
       byte[] bufferKey = new byte[256];
       InputStream is = new FileInputStream(in);
       if (is.read(bufferKey) != bufferKey.length) { 

       }
       is.close();

       Key ky = cipher.unwrap(bufferKey, "AES", Cipher.SECRET_KEY);¡

       // Now we must to uncrypt the rest of the file
       cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
       cipher.init(Cipher.DECRYPT_MODE, ky);

       CipherInputStream ix = new CipherInputStream(new FileInputStream(in), cipher);
       FileOutputStream os = new FileOutputStream(out);

       copy(ix, os);

       ix.close();
       os.close();

   } catch (Exception ex) {
       System.err.println("Ha succeït un error xifrant: " + ex);
   }
}

我需要在复制函数中进行哪些修改才能获取前256个字节后的字节数？我尝试了类似的东西，但它不起作用......

// Get the size of the file
long streamLength = inputStream.available();

if (streamLength > Integer.MAX_VALUE) {
    // File is too large
}

// Create the byte array to hold the data
byte[] bytes = new byte[1024];

// Read in the bytes
int block_size = 1024;
int offset = 256;
int numRead = 0;
while (offset < (int) streamLength && (numRead = inputStream.read(bytes, offset,  block_size)) >= 0) {
    offset += numRead;
    outputStream.write(bytes, 0 , block_size );
 }

Answer 1

您的解密代码应如下所示：

public static void fileDecryptWrapped(File in, File out, PrivateKey priv)
        throws GeneralSecurityException, IOException {

    Signature signature = Signature.getInstance("SHA1WITHRSA");
    signature.initSign(priv);
    signature.update("test".getBytes());
    byte[] bufferKey = signature.sign();

    // First we must to take the wrapped key in the first bufferKey.length bytes of the file
    InputStream is = new FileInputStream(in);
    if (is.read(bufferKey) != bufferKey.length) { 
        is.close();
        throw new IllegalStateException("Too short file");
    }

    Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
    cipher.init(Cipher.UNWRAP_MODE, priv);
    Key aesKey = cipher.unwrap(bufferKey, "AES", Cipher.SECRET_KEY);

    // Now we must to decrypt the rest of the file
    cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
    cipher.init(Cipher.DECRYPT_MODE, aesKey);

    CipherInputStream ix = new CipherInputStream(is, cipher);
    FileOutputStream os = new FileOutputStream(out);

    copy(ix, os);

    ix.close();
    os.close();
}

请注意，读取密钥后的FileInputStream传递给CipherInputStream而不做任何修改。

我用你的方法看到的问题，加密文件中没有结构。例如，使用非2K RSA密钥将严重失败，因为解密算法总是需要256字节的包装密钥。

加密在独特文件中附加包装密钥的文件

1 个答案: