A specification would be helpful in how this is to be implemented. The best I could find was http://en.wikipedia.org/wiki/Unicode#Input_methods and http://en.wikipedia.org/wiki/Alt_codes; though these are a little vague as to e.g. how long Alt must be held down, or whether decimal or hexadecimal, and neither mentions Ctrl key.
(Incidentally, you may also be interested in the Gnome Character Map program gucharmap, and http://en.wikipedia.org/wiki/Compose_key (useful for keyboard entry of common symbols like ‘’“”é槶™⁸⁹«»), and http://en.wikipedia.org/wiki/List_of_input_methods_for_UNIX_platforms for entering extended portions of text in other languages including CJK and indic.) pjrm.