Well, not sure about the encryption algorithm, but I don't think you want to unpack the thing as one giant hex number, which is what that unpack statement will do.

If these are 1-byte characters, the following will split up the string into chunks, pass them into unpack, then get the character represented:

print map { chr($_) } map {unpack("H2",$_) } $str =~ m/../g;
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For me, this yields the following string:

A$ A#??$'@& %&&=!=>B'@ @>>?BA&'B?%$= ==&"$@> "'"A'%@">&
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Is that closer to what you were looking for, or am I way off? :)