使用RSA Bouncy Castle加密/解密无法正常工作

Question

I'm trying to encryt/decrypt using RSAEngine library at bouncy castle, with a 2048 bit length key. I'm able to create the keys, store in different files and get from the files, but when I decrypt an image it makes something that I don't know that the file decrypted is not shown correctly.Files are created correctly,and I think the problem is at processBlock method while encrypting and/or decrypting.The code is the following to encrypt:

InputStream clearTextFile;
    FileOutputStream textFileProcessed=new FileOutputStream(fileName);
            //getKey is a method I implemented and works correctly
    RSAKeyParameters key=getKey(keyFileName);
    RSAEngine rsaEngine=new RSAEngine();
    rsaEngine.init(true,key);           
    clearTextFile=new FileInputStream(nameClearTextFile);
    byte[] bytesReaded;
    int nBytesReaded;
    int inputBlockSize=rsaEngine.getInputBlockSize();
    do
    {
        bytesReaded = new byte[inputBlockSize];
        nBytesReaded=clearTextFile.read(bytesReaded);
        if(nBytesReaded>-1)
        {       //This is for the last block if it's not 256 byte length
            if(nBytesReaded<inputBlockSize)
            {
                byte[] temp=new byte[nBytesReaded];
                for(int i=0;i<nBytesReaded;i++)
                {
                    temp[i]=bytesReaded[i];
                }
                byte[] encryptedText=rsaEngine.processBlock(temp,0,nBytesReaded);
                textFileProcessed.write(encryptedText);
            }
            else
            {
                byte[] encryptedText=rsaEngine.processBlock(bytesReaded,0,inputBlockSize);
                textFileProcessed.write(encryptedText); 
            }
        }
    }while(nBytesReaded>-1);
    textFileProcessed.flush();
    textFileProcessed.close();
    textFileProcessed.close();

And to decrypt:

InputStream encryptedTextFile=new FileInputStream(nameOfFile);
    OutputStream decryptedTextFile=new FileOutputStream(nameOfFile);
    RSAKeyParameters key=getKey(nameKeyFile);
    RSAEngine rsaEngine=new RSAEngine();
    rsaEngine.init(false,key);
    byte[] bytesReaded;
    int nBytesReaded;
    int inputBlockSize=rsaEngine.getInputBlockSize();
    do
    {
        bytesLeidos = new byte[inputBlockSize];
        nBytesReaded=encryptedTextFile.read(bytesReaded);
        if(nBytesReaded>-1)
        {
                byte[] decryptedText=rsaEngine.processBlock(bytesReaded,0,inputBlockSize);          
                decryptedTextFile.write(decryptedText);                 
        }
    }while(nBytesReaded>-1);
    decryptedTextFile.flush();
    decryptedTextFile.close();
    encryptedTextFile.close();

Thanks in advance

Answer 1

RSAEngine does not add padding, you will lose any leading zeros in your data blocks as a result. You need to use one of the encoding modes available as well.

I'd recommend using a symmetric key algorithm as well and just using RSA to encrypt the symmetric key. It will be a lot faster, and depending on your data, safer as well.

Regards,

David

Answer 2

I think you need to change this line:

   if(nBytesReaded>1)

to this

   if(nBytesReaded>-1)

And change this in the decypt part, maybe:

rsaEngine.init(false,clave);

to this

rsaEngine.init(false,key);

But there may be more. You aren't encrypting the whole input if the last block isn't full size.