I have used Acme::Bleach module to encrypt my cgi source code.

Beware, that is no encryption, just funny transliteration. Modules of the Acme namespace are generally not fit for production. There are exceptions, though - e.g. Acme::Code::Police.

after encrypting, my cgi source file just contains invisible character.

They are not invisible, they are just bleached. Perhaps rubbing them with tar adds some contrast.

Is their any specification related Acme::Bleach module and cgi.

No. You have to check the source to see where it breaks. But again, Acme::Bleach is for fun only. You might try encoding your code base64 (MIME::Base64), and have it decoded and executed on the fly on invocation. You could bleach that script... ;-)

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}