After it was working the way I liked, I did a search through past obfuscations at Perlmonks to make sure nobody else had done this before.  The only other submission I found which uses crypt was this one, but its method is significantly different.

One of the nice things about using crypt is that running perl -MO=Deparse on it doesn't give anything away.

(I decided to create a signature based on the idea, too, which I'll use for the first time here).

@::=qw'79 11 34 69 41 27 2 4 4 2 5 4';
@::_=map{$x=pop@::;(crypt$_.' ',shift@::)=~/..(.{$x}).*/g}
split/ /, 'writing Library. Building consider TO($FOO) *binary*';
map{print;/^[Hea]/ or print ' '}(@::_,',',$/)
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