Hello, Recently I got a PERL program written that will encrypt file using Blowfish.

The prefered spelling is "Perl", not "PERL".

What is difference between Blowfish and Blowfish_PP? Will the output differ if I change Blowfish to Blowfish_PP?

The file cryptdata.pl has the following line: use Crypt::Blowfish;. [...] can I change the line to use Crypt::Blowfish_PP; using NotePad?

Hopefully, speed is the only difference. Try it.

can I change the line:
my $proc = new Crypt::Blowfish $key_valid;
to
my $proc = new Crypt::BlowfishPP $key_valid;

That should be
my $proc = new Crypt::Blowfish_PP $key_valid;

The source file has: my $key = "My key" Now this key is in pure text format. How can I encrypt this key itself?

That won't accomplish what you desire, since you'd then need another plaintext key to decrypt the key.

You have two options:

• You could prompt for the key.

• You could control access to the .pl using your OS's permission system. Actually, Better yet, move the key to a seperate file and control access to both the .pl and the key file. That way, it's easier to use revisioning systems on the .pl, to make copies of the .pl, etc.

If this is not possible, then can I compile this cryptdata.pl file into an executable?

FAQ. Making an executable doesn't hide anything. It'll still be just as visible to the trained eye.