About the passphrase

Hello there. I have a question about the passphrase process.
As far as I could see, when I generate the private key and the public key, the passphrase is used to encrypt this private key, right? This would be a symetric encryption algorithm then. What is this algorithm? AES? What is the size of the key?
I’m asking this because I want to understand the difficulty in cheating the system when you have other person’s public and private key but not the passphrase.
Thanks a lot.

Andre - Brazil

I think is really a question which should go
to the gnupg-devel or gnupg-users mailing lists.
There, all the crypto experts hang around and
can answer base cryptography questions.
I also guess, there must exist some documentation
about this question already, because it is
a typical question.
Have you tried search engines already?

Thanks for answering Jan, I did tried to google it but all I find is those ordinary explanation about PGP and assymetric criptography. I’ll try to post this into this lists you recommended.

I just searched in the www and found this german page:
(German GnuPG Manual)
There is written that the default hash algorithm of the passphrase is SHA-1, and then the private key is symmetrically encrypted with CAST-5. You can overwrite these defaults with s2k-digest-algo Name and s2k-cipher-algo Name.