I think holli is right. You need to do some reading on the basics of how public-key cryptography works. The whole point is that you can safely exchange your public keys with anyone.

Now, that being said, you might want to use conventional (symetric) encryption, which does use one, shared private key/password to decrypt. That's entirely different, and a bit problematic on the internet. (If you have a safe way to send your shared password out, then you also have a safe way to send your message in the first place.)

You definitely need to bone up on cryptography before you start asking perl questions.

Wikipedia on PGP

If you want to do symetric encryption with perl, I suggest Crypt::Blowfish.

Finally the standard book on all things crypto is Schneier's Applied Cryptography

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