And expensive, creating a string for each hex digit.  It'd be better to do something like https://github.com/dotnet/corefx/blob/2ea446cc13790ae5ccdff1b2df155d2d6680e6d9/src/System.Security.Cryptography.X509Certificates/src/Internal/Cryptography/Helpers.cs#L38 but without all of the whitespace goo stuff. 