It's actually somewhat robust...sort of. It could be shorter, but at the cost of an increase in clarity (in my opinion).

#!/usr/bin/perl -lp

$?*=!$$?%,:$s;s.[g-z]|\W..gi;$;=(chomp,length);for(split//){s}
(\w)}\U$1}gx;$_=+(ord)-55if(ord>$=);$?+=(16**--$;)*$_}s;$_;$?;
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Brandan L.