openpgp-notes/book/source/10-encryption.md

(encryption_chapter)=

Encryption

Encryption is one of the core facilities of OpenPGP. It provides confidentiality.

High-Level overview of the message encryption process

Core concept:

• The plaintext is encrypted with a symmetric "session key."
• The "session key" itself is stored in encrypted form, possibly multiple times:
  • The session key is encrypted to the encryption keys of each intended recipient of the message.
  • Alternatively, or additionally, the session key may be encrypted using a passphrase (this mode of operation doesn't require any OpenPGP certificates.)

Generations of encryption

SEIPD w/ AEAD (v2)

SEIPD (v1)

Advanced topics

Encrypt for multiple/single subkey per certificate?

"Negotiating" algorithms based on recipients preference subpackets

Prevent "downgrade" -> Policy

Implications of how a recipient cert is "addressed" (fingerprint/key-ID vs. user-ID) (preferences, expiration, revocation)

AEAD modes: GCM

:class: warning

Produce text around discussion: https://mailarchive.ietf.org/arch/msg/openpgp/ZTYD5VJsG1k2jJBbn5zIAf5o7d4/

Zooming in: Packet structure

Encryption yields a 'wrapped' openpgp packet stream

SKESK

Also see https://flowcrypt.com/docs/guide/send-and-receive/send-password-protected-emails.html