https://github.com/jruby/jruby/blob/master/lib/ruby/shared/krypt.rb contains require_relative, so it is not 1.8-compatible. I haven't looked at the code in detail, so I am not sure how reliant krypt is on 1.9 features.

If we can't bend it to fit, we should postpone incorporating it until we drop the 1.8 support, or devise a means to disable krypt in the 1.8 mode.