key file support

[clach04]

1. PT (like Tombo, VimVry6, and AESZip) use a passphrase only (possibly with key derivation function) for encryption/decryption
2. Many tools (like Opengpg, age, etc.) Use a key file (typically on disk, but not always) that is protected by a passphrase (typically, but not always) that maybe accessed via an agent or keyring. For:
   a. Symmetric encryption/decryption.
   b. Public/private key pair encryption/decryption.

Many tools transparently will handle 2.b. for decryption.
For 2.a and 2.b (for encryption) what would the work flow/UX be for an end user of PT?

[clach04]

Environment variables

Environment variables could name key, either generic variable or one variable per encryption backend. Example:

• gpg - PT_KEY_GPG
• age - PT_KEY_AGE
• etc.

Config file

Right now, encryption classes do not have access to config.

overload passphrase

Passphrase could be keyname:passphrase for key.