[Someone1234]

Not that this matters to your overall point, but base64 isn't actually a valid format to use in a parameter as a base64 string can legally contain: '+', '/' and '=' which would be interpreted and corrupt the data.

In the .Net world you'll want to use something like HttpServerUtility.UrlTokenEncode()/UrlTokenDecode() since it gives you a base64-like string with '+', '/' and '=' replaced or removed.

[kej]

You can use base 64 with a URL-safe alphabet, as specified in RFC 4648: http://tools.ietf.org/html/rfc4648#page-7