asc and pgp

These are definitions you will get if you Google.

- An ASC file is an armored ASCII file used by Pretty Good Privacy (PGP), an encryption program utilized for secure communication. It contains a digitally signed message and may store plain-text written information, as well as binary information encoded as text.

- Pretty Good Privacy is an encryption program that provides cryptographic privacy and authentication for data communication. PGP is used for signing, encrypting, and decrypting texts, e-mails, files, directories, and whole disk partitions and to increase the security of e-mail communications.

If you can't understand the above (I can't too :P), according to me in layman's language it means PGP encryption is used for encrypting communications (SSH is also a way to communicate). ASC file is used by PGP. With the passphrase we get after decrypting asc file, can be used to decrypt pgp keys.