Is there any restriction of my Key Length passed to encoding using ASCIIEncoding in .NET 4.0?

Question

I am using C# 4.0 Windows Application.I want to give encryption key to protect my file using System.Text.ASCIIEncoding.So, Here my encryption key is SARAVANAN and key length of this is 9.

 String enKey="SARAVANAN";
 DESCryptoServiceProvider des = new DESCryptoServiceProvider();
 des.Key = ASCIIEncoding.ASCII.GetBytes(enKey);

it raised the exception like "Specified key is not a valid size for this algorithm".But it is working good at length of 8 only.So,i would like to know is there any restriction to this length due to this ASCII ENCODING...

Please guide me get out of this issue?

Answer 1

64 bits is the only valid key size for the DES encryption algorithm.

ASCII encoding uses 8 bits per character, therefore 8 ASCII characters == 64 bits.

Answer 2

It's got nothing to do with ASCIIEncoding. It's to do with DESCryptoServiceProvider. From the documentation:

This algorithm supports a key length of 64 bits.

In other words, the key you pass in should be 64 bits, or 8 bytes. How you get those 8 bytes is up to you - but the ASCII-encoded form of a 9-ASCII-letter string is going to be 9 bytes (72 bits).

Answer 3

If you take a look at MSDN you can see This algorithm supports a key length of 64 bits. So the only valid length for a key is 8 characters.