AES CTR Mode with Bouncycastle Cryptography
aes, bouncycastle, c#, cryptography, rijndaelmanaged
Solution
You don't need to use `PaddedBufferedBlockCipher` at all. Counter mode encryption is a streaming mode for a block cipher. Streaming ciphers don't need padding.
You can use `BufferedBlockCipher` to access the streaming mode as `SicBlockCipher` only lets you encrypt one block at a time.
Problem
I am trying to use to implement AES CTR encryption using the Bouncy castle cryptography library in C#. .NET provides RijndaelManaged Crypto Library but it does not support CTR mode for AES hence the selection of Bouncycastle. I haven't been able to code it properly The problem seems to be with IV. ``` public string BytesToHex(byte[] bytes) { char[] c = new char[bytes.Length * 2]; byte b; for (int bx = 0, cx = 0; bx < bytes.Length; ++bx, ++cx) { b = ((byte)(bytes[bx] >> 4)); c[cx] = (char)(b > 9 ? b + 0x37 + 0x20 : b + 0x30); b = ((byte)(bytes[bx] & 0x0F)); c[++cx] = (char)(b > 9 ? b + 0x37 + 0x20 : b + 0x30); } return new string(c); } public byte[] HexToBytes(string str) { if (str.Length == 0 || str.Length % 2 != 0) return new byte[0]; byte[] buffer = new byte[str.Length / 2]; char c; for (int bx = 0, sx = 0; bx < buffer.Length; ++bx, ++sx) { // Convert first half of byte c = str[sx]; buffer[bx] = (byte)((c > '9' ? (c > 'Z' ? (c - 'a' + 10) : (c - 'A' + 10)) : (c - '0')) << 4); // Convert second half of byte c = str[++sx]; buffer[bx] |= (byte)(c > '9' ? (c > 'Z' ? (c - 'a' + 10) : (c - 'A' + 10)) : (c - '0')); } return buffer; } private static byte[] cipherData(PaddedBufferedBlockCipher cipher, byte[] data) { int minSize = cipher.GetOutputSize(data.Length); byte[] outBuf = new byte[minSize]; int length1 = cipher.ProcessBytes(data, 0, data.Length, outBuf, 0); int length2 = cipher.DoFinal(outBuf, length1); int actualLength = length1 + length2; byte[] result = new byte[actualLength]; Array.Copy(outBuf,result,actualLength); //System.arraycopy(outBuf, 0, result, 0, result.length); return result; } private static byte[] decryptCTR(byte[] cipher, byte[] key, byte[] iv) { //Org.BouncyCastle.Crypto.Modes.SicBlockCipher PaddedBufferedBlockCipher aes = new PaddedBufferedBlockCipher(new SicBlockCipher(new AesEngine())); ParametersWithIV ivAndKey = new ParametersWithIV(new KeyParameter(key), iv); aes.Init(false, ivAndKey); return cipherData(aes, cipher); } private static byte[] encryptCTR(byte[] plain, byte[] key, byte[] iv) { PaddedBufferedBlockCipher aes = new PaddedBufferedBlockCipher(new SicBlockCipher( new AesEngine())); ParametersWithIV ivAndKey = new ParametersWithIV(new KeyParameter(key), iv); aes.Init(true, ivAndKey); return cipherData(aes, plain); } ``` And I am trying to decrypt a given cipher text using the following method ``` private void btnDecryptDirectly_Click(object sender, EventArgs e) { String encodedMsgHex = "770b80259ec33beb2561358a9f2dc617e46218c0a53cbeca695ae45faa8952aa0e311bde9d4e01726d3184c34451"; String key = "36f18357be4dbd77f050515c73fcf9f2"; byte [] keyBytes = HexToBytes(key); byte[] cipher = HexToBytes(encodedMsgHex); txtDecryptedText = BytesToHex(decryptCTR(cipher, keyBytes, IV)); rtbDecrypted.Text = txtDecryptedText; } ``` Every time I run this I get error the last block incomplete in decryption Error. Can any one please help me out.