Re: a problem with encryption

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Date: Tue, 10 Aug 2004 13:32:19 -0700

>The problem is that you're assuming the decrypted size will be the same
as the encrypted size - it's not. You're only actually reading 15 bytes
(and moreover, you're assuming they'll all be read in one go, which is a
bad idea) but passing the encoding a buffer 16 bytes long.
>*Always* use the return value of Stream.Read.

Well, the problem was not in network operations and data send. It was in
decrypted data.
The problem was I did always get n to 16 bytes filled with zeros.

So I've just swapped line:

roundtrip = textConverter.GetString(fromEncrypt);

with:

roundtrip =
textConverter.GetString(fromEncrypt).TrimEnd(Convert.ToChar(0));

That way I always get the original data I've encrypted.

Thanks btw.

I have another question:
When I'm sending this data trough network stream from client to server,
I always create byte type array big enough to accept possible data from
the client application.
Do I have to always create it big enough to support any possible data
size, or I can read everything in blocks and then merge it to a single
byte array for example.

This is how it is done by now:

client code:
(this is a connection thread code cut from the main code:)

try
{
this.hostName = this.textBox2.Text;
TcpClient client = new TcpClient(hostName, portNum);

NetworkStream ns = client.GetStream();

//size of response buffer
byte[] bytes = new byte[1024];

//using custom encryption class to encrypt given data
bit256_RijndaelEnCryptorC enkripted = new bit256_RijndaelEnCryptorC();

//encrypt string from the textbox
encrypted.EnCrypt(this.textBox1.Text);

//create data-to-be-sent buffer
byte[] byteTime = new byte[encrypted.ReleaseEnCrypted).Length];

//fill it
byteTime = encrypted.ReleaseEnCrypted();

//write it trough stream
ns.Write(byteTime, 0, byteTime.Length);

//receive a response
int bytesRead = ns.Read(bytes, 0, bytes.Length);

client.Close();

}

server code:

TcpClient client = listener.AcceptTcpClient();

NetworkStream ns = client.GetStream();

//buffer for incoming data
byte[] bytes = new byte[4096];

//read data from the ns
int bytesRead = ns.Read(bytes, 0, bytes.Length);

//input data in a work buffer
byte[] returned = new byte[bytesRead];

for (int u=0; u<bytesRead; u++)
{
    returned[u]=bytes[u];
}

//create data variables to be used in encryption process
byte[] key = new byte[32];
byte[] IV = new byte[16];
byte[] encrypted = new byte[returned.Length-48];

//strip usable data from the incoming stream
for (int i=0; i<32; i++)
{
    key[i]=returned[i];
}
for (int i=32; i<48; i++)
{
    IV[i-32]=returned[i];
}
for (int i=48; i<returned.Length; i++)
{
    encrypted[i-48]=returned[i];
}

//create a custom encryption (this time decryption) class
bit256_RijndaelEnCryptorC dekripted = new
bit256_RijndaelEnCryptorC(key,IV,encrypted);
encrypted.DeCrypt();

string result = encrypted.ReleaseDeCrypted();

byte[] byteTime = Encoding.ASCII.GetBytes("server performed
operations!");

try
{
    ns.Write(byteTime, 0, byteTime.Length);
    ns.Close();
}
client.Close();

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• Previous message: Bob Powell [MVP]: "Re: REPOST: Displaying and Editing a Time value in a PropertyGrid"
• In reply to: Jon Skeet [C# MVP]: "Re: a problem with encryption"
• Next in thread: Jon Skeet [C# MVP]: "Re: a problem with encryption"
• Reply: Jon Skeet [C# MVP]: "Re: a problem with encryption"
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