vanitasvitae/openpgp-notes
1
0
Fork 0
mirror of https://codeberg.org/openpgp/notes.git synced 2024-11-22 23:52:05 +01:00
Code Issues Projects Releases Packages Wiki Activity

edit on ch6 verifying packet section and subpackets

Browse source
This commit is contained in:
Tammi L. Coles 2023-11-10 15:41:11 +01:00
parent 3dcc962c57
commit 18a621c827
1 changed files with 6 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

11
book/source/06-signatures.md
View file

@ -101,13 +101,14 @@ Verifying a signature in OpenPGP
(signature_subpackets)=
## Signature subpackets
A bare cryptographic signature - even when combined with a signature type ID - is usually not sufficiently expressive. So, to encode additional metadata in signature packets, the OpenPGP protocol introduced signature subpackets (in [RFC 2440](https://datatracker.ietf.org/doc/html/rfc2440)).
In the OpenPGP protocol, signature subpackets enhance the expressiveness of a signature beyond what is conveyed by just the bare cryptographic signature and the signature type ID. These subpackets, introduced in [RFC 2440](https://datatracker.ietf.org/doc/html/rfc2440), are essential for embedding additional metadata within signature packets.
Subpackets are well-defined data structures that can be placed into signature packets as sub-elements. They provide additional context and meaning for a signature. Subpackets encode data in a key-value format. The RFC defines all possible keys as [subpacket type IDs](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-signature-subpacket-types-r) and provides the value format (and meaning) for all of them.
Signature subpackets serve as sub-elements within signature packets, providing extra context and meaning to a signature.
They are formatted as key-value pairs, where the keys are defined as [subpacket type IDs](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-signature-subpacket-types-r) by the RFC. The RFC also provides the format and interpretation of the values.
Typical examples are:
- The [*issuer fingerprint*](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#issuer-fingerprint-subpacket) subpacket, which encodes the fingerprint of the component key that issued the signature, or
- The [*key flags*](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-key-flags) subpacket, that defines which capabilities are assigned to a component key, in a certificate.
### Examples of signature subpackets:
- The [*issuer fingerprint*](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#issuer-fingerprint-subpacket) subpacket encodes the fingerprint of the component key that issued the signature.
- The [*key flags*](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-key-flags) subpacket defines the capabilities are assigned to a component key within a certificate.
### Hashed and unhashed signature subpackets