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33 lines
1.7 KiB
Markdown
33 lines
1.7 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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# Advanced material: Encryption
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## Encrypt to multiple/single subkey per certificate?
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A recipient's certificate can contain more than one usable encryption subkey.
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This raises the question, should the message be encrypted for all of them?
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There is the argument that a powerful attacker might have managed to add an attacker-controlled encryption subkey to the victim's certificate.
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In this case, only encrypting to the "newest" encryption key would help uncover such an attack. However, a powerful attacker could just MitM any sent messages and just add a PKESK for the victim-controlled encryption keys to hide the fact that the sender used a different key.
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On the other hand, a user might have multiple encryption subkeys on purpose.
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Picture, for example, a scenario where the same certificate is used on multiple devices, but each device has dedicated encryption subkeys to allow for smoother revocation in case of a lost device.
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In this scenario, it is important that the sender encrypts the message to all available encryption subkeys.
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## "Negotiating" algorithms based on recipients preference subpackets
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### Prevent "downgrade" -> Policy
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Each implementation should define a "minimum" level of security when it comes to algorithms and key lengths.
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If the lowest common denominator of symmetric encryption algorithms preferred by a set of recipients provides too little security, the implementation should either use a configured fallback algorithm instead, or fail to produce a message at all.
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## AEAD modes in v2 SEIPD: GCM
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```{note}
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This section is still about to be written.
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```
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