Encrypt and URL disallowed characters - alphanumeric option?

[eluser]Yash[/eluser]
I'm confuse what exactly you want.

I want to avoid allowing more characters in $config[‘permitted_uri_chars’]

then add all characters you want

Is there a way to restrict the encryption to alphanumeric characters only?

don't use dohash use random generator function can only give you alphanumeric