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57 lines
2.2 KiB
Markdown
57 lines
2.2 KiB
Markdown
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SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
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SPDX-License-Identifier: CC-BY-SA-4.0
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-->
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(encryption_chapter)=
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# Encryption
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[Encryption](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-10.html#section-2.1) is one of the core facilities of OpenPGP. It provides confidentiality.
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## High-Level overview of the message encryption process
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Encryption in OpenPGP uses a [hybrid cryptosystem](hybrid_cryptosystems).
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This means that two distinct steps are performed:
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- Encryption of the plaintext with a (secret) symmetric key, the *message key*. The (potentially large) payload only needs to be stored once: all recipients can decrypt the same symmetrically encrypted ciphertext, using this single message key.
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- This symmetric message key is then stored in encrypted form, possibly multiple times, once for each recipient.
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- Usually, the symmetric key is encrypted to a public encryption component key of the recipient.
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- Alternatively - or additionally - the secret symmetric key may also be encrypted using a passphrase, in place of an asymmetric key. This is a specialized and less commonly used mode of operation that doesn't require OpenPGP certificates.
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## Generations of encryption
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There are two generations of OpenPGP's encryption mechanism that the RFC allows for producing new encrypted messages, see [Packet Versions in Encrypted Messages](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#section-10.3.2.1).
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(SEIPDv2)=
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### SEIPD w/ AEAD (v2)
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New in OpenPGP version 6.
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### SEIPD (v1)
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## Advanced topics
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### Encrypt for multiple/single subkey per certificate?
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### "Negotiating" algorithms based on recipients preference subpackets
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#### Prevent "downgrade" -> Policy
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### Implications of how a recipient cert is "addressed" (fingerprint/key-ID vs. user-ID) (preferences, expiration, revocation)
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### AEAD modes: GCM
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```{admonition} TODO
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:class: warning
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Produce text around discussion: https://mailarchive.ietf.org/arch/msg/openpgp/ZTYD5VJsG1k2jJBbn5zIAf5o7d4/
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```
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## Zooming in: Packet structure
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### Encryption yields a 'wrapped' openpgp packet stream
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### SKESK
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Also see https://flowcrypt.com/docs/guide/send-and-receive/send-password-protected-emails.html
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