I know question #2, chr() and ord()

#!/usr/bin/perl -w
use strict;

printf "%X\n", ord('a');  #61
printf "%X\n", ord('b');  #62
print chr(0x61);          #a
[download]

still working on the best formulation for question #1. An issue is how to make it efficient.

Update: I think Moritz is on it.

pack() and unpack() are cool critters, but sometimes you have to stare at it for awhile. Example from the doc's:
sub ordinal { unpack("W",$_[0]); } # same as ord()

ord() and chr() are pretty "lightweight" critters. Without testing, I don't know if some kind of substr() based approach would be slower or faster. I assume for crypto, speed would be a major factor. On this performance point, I just don't know at the moment.