"Length of the data to decrypt is invalid." exception during Rijndael decryption - exception

Question

I get "Length of the data to decrypt is invalid." exception when i try to decrypt a memory stream. I am beginner, cant figure out whats wrong. whats wrong?
public bool EncryptStream()
{
string password = #"myKey123"; // Your Key Here
UnicodeEncoding UE = new UnicodeEncoding();
byte[] key = UE.GetBytes(password);
s_EncryptedStream = new MemoryStream();
int NoOfBytes;
byte[] b_Buffer = new byte[8192];
s_MemoryStream.Seek(0, SeekOrigin.Begin);
RijndaelManaged RMCrypto = new RijndaelManaged();
s_CrytpoStream = new CryptoStream(s_EncryptedStream,
RMCrypto.CreateEncryptor(key, key),
CryptoStreamMode.Write);
while (s_MemoryStream.Length < s_MemoryStream.Position)
{
NoOfBytes = s_MemoryStream.Read(b_Buffer, 0, 8192);
s_CrytpoStream.Write(b_Buffer, 0, NoOfBytes);
}
s_MemoryStream.Seek(0, SeekOrigin.Begin);
while (s_EncryptedStream.Position < s_EncryptedStream.Length)
{
NoOfBytes = s_EncryptedStream.Read(b_Buffer, 0, 8192);
s_MemoryStream.Write(b_Buffer, 0, NoOfBytes);
}
s_CrytpoStream.Flush();
s_CrytpoStream.Close();
return true;
}
public bool DecryptStream()
{
string password = #"myKey123"; // Your Key Here
UnicodeEncoding UE = new UnicodeEncoding();
byte[] key = UE.GetBytes(password);
int NoOfBytes;
byte[] b_Buffer = new byte[8192];
s_DecryptedStream = new MemoryStream();
RijndaelManaged RMCrypto = new RijndaelManaged();
s_CrytpoStream = new CryptoStream(s_MemoryStream,
RMCrypto.CreateDecryptor(key, key),
CryptoStreamMode.Read);
s_MemoryStream.Seek(0, SeekOrigin.Begin);
while (s_MemoryStream.Length > s_MemoryStream.Position)
{
NoOfBytes = s_CrytpoStream.Read(b_Buffer, 0, 8192);
s_DecryptedStream.Write(b_Buffer, 0, NoOfBytes);
}
s_DecryptedStream.Seek(0, SeekOrigin.Begin);
s_MemoryStream.Seek(0, SeekOrigin.Begin);
while (s_DecryptedStream.Position < s_DecryptedStream.Length)
{
NoOfBytes = s_DecryptedStream.Read(b_Buffer, 0, 8192);
s_MemoryStream.Write(b_Buffer, 0, NoOfBytes);
}
s_CrytpoStream.Flush();
s_CrytpoStream.Close();
return true;
}

Answer 1

For a start, this while loop condition is never right:
while (s_MemoryStream.Length < s_MemoryStream.Position)
How can the position be beyond the length?
Rather than using the length of a stream, the usual pattern to copy a stream is to read repeatedly until the value returned isn't positive. As you're doing that twice in this code anyway, you might as well encapsulate it:
public static void CopyStream(Stream input, Stream output)
{
byte[] buffer = new byte[8192];
int read;
while ( (read = input.Read(buffer, 0, buffer.Length)) > 0)
{
output.Write(buffer, 0, read);
}
}
It's also best to use using statements to clean up strings. Additionally, the Encoding.Unicode property means you don't have to create a new UnicodeEncoding yourself. Also, I generally find that setting the Position property is more readable than using Seek. Finally, there's no point in a method returning a value if it's always going to be true. So, your code would become:
public void EncryptStream()
{
string password = #"myKey123"; // Your Key Here
byte[] key = Encoding.Unicode.GetBytes(password);
s_EncryptedStream = new MemoryStream();
s_MemoryStream.Position = 0;
RijndaelManaged RMCrypto = new RijndaelManaged();
using (Stream crytpoStream = new CryptoStream(s_EncryptedStream,
RMCrypto.CreateEncryptor(key, key),
CryptoStreamMode.Write))
{
CopyStream(s_MemoryStream, cryptoStream);
}
s_MemoryStream.Position = 0;
s_EncryptedStream.Position = 0;
CopyStream(s_EncryptedStream, s_MemoryStream);
}
public void DecryptStream()
{
string password = #"myKey123"; // Your Key Here
byte[] key = Encoding.Unicode.GetBytes(password);
s_DecryptedStream = new MemoryStream();
s_MemoryStream.Position = 0;
RijndaelManaged RMCrypto = new RijndaelManaged();
using (Stream crytpoStream = new CryptoStream(s_MemoryStream,
RMCrypto.CreateDecryptor(key, key),
CryptoStreamMode.Read))
{
CopyStream(cryptoStream, s_DecryptedStream);
}
s_DecryptedStream.Position = 0;
s_MemoryStream.Position = 0;
CopyStream(s_DecryptedStream, s_MemoryStream);
}
Even after amending this code, it feels like you've got way too many non-local variables here. I can't see why any of this should be in instance variables. Make the stream to be encrypted or decrypted a parameter (along with the password) and return a memory stream with the encrypted/decrypted data in, or just a byte array.

Answer 2

You may need to call the FlushFinalBlock method on the CryptoStream after you have finished reading the input data. (ie. crytpoStream.FlushFinalBlock() after CopyStream)

Answer 3

I have come up with a solution and I have it posted on my new Blog
constotech.blogspot.com/2009/05/net-encryption-using-symmetricalgorithm.html