If you're going to do that you might as well do

#!/usr/bin/perl

@list = split //, 'ABCDEFGH';

s&&local$/;
<DATA>&e&&y&;
&&d;& s#zoTfFdDsOt##g;
while/(\D)(\d+)/gi;

sub z{(&O-&O)*((&O-&O)*(&O-&O))}
sub o{&z-((&O-&O)*(&O-&O))+&O-&O}
sub T{&z-(&O-&O)}
sub f{&T+(&O-&O)}
sub F{(&O-(&O-&O))/(&O-&O)}
sub d{print chr shift}
sub D(@){map chr,@_}
sub s{print D$1->(@list[split//,$2])}
sub O{ord shift}
sub t{&z+&O-&O(A)}
__DATA__
#t50703010o507040703002o507040703004o507040703003F01020f5070
306057t50703050t50703060o507040703003T50703010T50703040o5070
40703005F01020t50703070T50703040o507040703005t50703030F01020
T50703010f5070306057T50703060t50703020T50703040o507040703005
[download]

Proves the same point!