how to pad data before encryption with Bouncy Castle
aes, c#, cryptography
Solution
Bouncy Castle will do the padding for you, to start you need to set up your cihper as:
PaddedBufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new CbcBlockCipher(engine), new Pkcs7Padding());
For the rest of your code to work would need to use `cipher.GetOutputSize(data.Length)` `ProcessBytes`,and `DoFinal` so the padding is added correctly.
byte[] output = new byte[cipher.GetOutputSize(data.Length)];
int len = cipher.ProcessBytes(data, 0, data.Length, output, 0);
cipher.DoFinal(output, len);
I have a simple example on of using AES-GCM in Bouncy Castle on CodeReview
AES-GCM adds authenticated encryption, but the basic principle of using the api is the same.
I also have a C# port of high level encryption framework, Kecyzar, that I used Bouncy Castle as the backend, although it's a harder example, the abstracted encryption code SymmetricStream is setup for using AES-CBC in BouncyAesKey
Problem
I'm trying to encrypt my data with AES algorithm with CBC mode. For this reason I use .Net Library 'Bouncy Castle'. I have not a background in crypto, so I'm trying to use it in a straightforward way. Here is my encrypt code ``` public byte[] encrypt(byte[] key, byte[] iv,byte[] data) { IBlockCipher engine=new AesFastEngine(); KeyParameter keyParam = new KeyParameter(key); CbcBlockCipher cipher = new CbcBlockCipher(engine); ICipherParameters parameters = new ParametersWithIV(keyParam, iv); byte[] output=new byte[16+data.Length]; cipher.Init(true, parameters); cipher.ProcessBlock(data, 0, output, data.Length); //process output byte[] cipherArray = new byte[data.Length]; /* int k=0; for (int i = 0; i < output.Length; i++) { if (output[i]!= 0) { cipherArray[k++] = output[i]; } } */ return cipherArray; } ``` When I try an input that is not a multiply of 16, I get an exception. When I pad the array to the right with a number of (16-length%16) with zeros on the left, I can get a result. But the result is a problem for me as well. It gives me a result like this: ``` [0][0][0][0[111][22][33][44][66][77][33][12][32][23][0][0][0][0][0] ``` zeros on the both left and right. I thought it may be about my use of `ProcessBlock(data, 0, output, data.Length)` function. I use it with the assumption that output will be my ciphered text, but it seems that output should be longer than the input length. since I don't have a documentation about this function, I may be using it in a wrong way. Any help would be appreciated