Is creating a Guid out of an MD5 hash instead of String valid?

Question

I am trying to implement a method for detecting duplicate files. I have an MD5 hashing method (let's ignore the fact that MD5 is broken) as below:

using(MD5 hasher = MD5.Create())
using(FileStream fs = File.OpenRead("SomeFile"))
{
    byte[] hashBytes = hasher.ComputeHash(fs);
    string hashString = string.Join(string.Empty, hashBytes.Select(x => x.ToString("X2"))); 
}

Instead of creating a string out of the hashBytes can I simply create a Guid out of it like so?

Guid hashGuid = new Guid(hashBytes);

Would it still be valid or will I lose uniqueness?

Answer 1

MD5 hashes and Guid essentially both express 128 bits of binary, so:

• plus: you won't lose any uniqueness
• plus: the fact that Guid is a value-type means that you avoids an allocation compared to string...
• minus: ... but if you're going to display it anywhere, you might actually end up allocating multiple strings (i.e. rendering the same Guid multiple times)
• minus: there is a semantic meaning to Guid that won't really be respected/expected here
• minus: Guid default formatting isn't the same as how MD5 hashes are usually expressed
• minus: Guid endianness is a mess, so if you want to get between raw bytes and any text representation: tread very carefully; it is not what you expect