Is there a file upload control for ASP.Net which performs a client-side checksum calculation (CRC, MD5, etc) on the file contents and transmits the checksum to allow for server-side checksum validation?
I have looked through answers on several file upload questions, but did not find this feature mentioned anywhere.
You'll need some client code to open your file, compute that check sum and to post it to your webserver with your file content; you can't do that with plain javascript, as you're not supposed to have access to your user filesystem.
But, just like @Dan Herbert commented out into your question, to use a client application like Flash, Java applet or Silverlight to execute that. I just wanted to make a more complete answer and to explain why you can't do that.
From javascript you won't be able to detect the size of a file in the client computer. Javascript runs inside a sandbox and cannot access local system files, which will be a ecurity violation.
You can use silverlight and can get the file size and calculate the sum. You can check this