title: Quickly determining if a set of files are identical in C#?
body: <p>I have the need to relatively quickly be able to determine if a set of files on a user's machine has been processed before by my application. The app in question uploads the files for the user to a server, and if the files have been uploaded before, it skips the upload. My plan so far has been to hash the files and then store the results along with an identifier of how they were uploaded to the server. The problem I think I'm going to run into is that storing this data could become quite cumbersome due to the length of the hashes. I'm expecting around 30-40 files right now but that could double or (hypothetically) even triple. </p>
  
  <p>Would this be possible to store using a Dictionary, with the hashes as the key and the server information as the value? I would then have that Dictionary stored in the App's Properties.Settings.Default object. Is that feasible to store with that system or will I run into some sort of problem there? Note that due to the nature of the application, there is <em>no</em> chance of two users ever having the same set of data, so I don't need to compare uploads between users. Additionally, what would the performance be like for this type of operation? Users are expected to have at least a Pentium-M 1.5 GHz processor with 1 GB of RAM.</p>