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@ -214,19 +214,21 @@ Notably, in many algorithms, encryption and signing-related functionalities (i.e
### Algorithm preferences and feature signaling
OpenPGP has a lot of ["cryptographic agility"](https://en.wikipedia.org/wiki/Cryptographic_agility). That is, OpenPGP doesn't just use one fixed set of algorithms, but defines a suite of cryptographic primitives that users (or their applications) can pick from.
OpenPGP demonstrates significant ["cryptographic agility"](https://en.wikipedia.org/wiki/Cryptographic_agility). It doesn't rely on a single fixed set of algorithms. Instead, it defines a suite of cryptographic primitives from which users (or their applications) can choose.
This agility has the advantage that adoption of new cryptographic primitives into the standard is relatively easy, and can be done without disruption. Users can gradually migrate to using new cryptographic mechanisms.
This agility facilitates the easy adoption of new cryptographic primitives into the standard, allowing for a seamless transition. Users can gradually migrate to new cryptographic mechanisms without disruption.
However, it also means that OpenPGP software needs to figure out which mechanisms a set of communication partners can handle and prefer. To do this, there are a number of mechanisms in OpenPGP that can be negotiated between sender and recipient. Note that OpenPGP is not an online scheme, so this negotiation is effectively one-way: The active party interprets the preferences that are expressed in the certificate of the passive party.
However, this approach requires that OpenPGP software determine the cryptographic mechanisms that a set of communication partners can handle and prefer. OpenPGP employs several mechanisms for this purpose, which allow negotiation between sender and recipient. It's important to note that OpenPGP is not an online scheme; thus, this negotiation is effectively one-way. The active party interprets the preferences expressed in the certificate of the passive party.
- [Preferred Hash Algorithms](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#preferred-hashes-subpacket)
- [Preferred Symmetric Ciphers for v1 SEIPD](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#preferred-v1-seipd)
- [Preferred AEAD Ciphersuites](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#preferred-v2-seipd)
- [Features](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#features-subpacket)
- [Preferred Compression Algorithms](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#preferred-compression-subpacket)
Key negotiation mechanisms in OpenPGP include:
In addition to these explicitly expressed preferences, implementations also deduce capabilities of communication partners based on the OpenPGP version of the certificate that they write to.
- [Preferred hash algorithms](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#preferred-hashes-subpacket)
- [Preferred symmetric ciphers for v1 SEIPD](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#preferred-v1-seipd)
- [Preferred AEAD ciphersuites](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#preferred-v2-seipd)
- [Features subpacket](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#features-subpacket)
- [Preferred compression algorithms](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#preferred-compression-subpacket)
Beyond these explicitly expressed preferences, implementations also deduce capabilities of communication partners based on the version of the OpenPGP certificate they possess.
#### User ID-specific preferences