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ch6: rfc links

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Heiko Schaefer 2023-10-28 13:43:41 +02:00
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6
book/source/06-signatures.md
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@ -71,8 +71,8 @@ Just a cryptographic signature, combined with a signature type identifier, is of
Subpackets are well-defined data structures that can be placed into signature packets as subelements. They give additional context and meaning to a signature. Subpackets encode data in a key-value format. All possible keys are defined in the RFC as [subpacket type IDs](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-signature-subpacket-types-r), and the value format (and meaning) are defined in the RFC for each subpacket type ID. Subpackets are well-defined data structures that can be placed into signature packets as subelements. They give additional context and meaning to a signature. Subpackets encode data in a key-value format. All possible keys are defined in the RFC as [subpacket type IDs](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-signature-subpacket-types-r), and the value format (and meaning) are defined in the RFC for each subpacket type ID.
Typical examples are: Typical examples are:
- the *issuer fingerprint* subpacket, which contains the fingerprint of the issuer key, or - the [*issuer fingerprint*](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#issuer-fingerprint-subpacket) subpacket, which contains the fingerprint of the issuer key, or
- the *key flags* subpacket which defines what purpose a component key is used for, in a certificate. - the [*key flags*](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-key-flags) subpacket which defines what purpose a component key is used for, in a certificate.
Signature subpackets can reside in two different areas of a signature packet: Signature subpackets can reside in two different areas of a signature packet:
@ -88,7 +88,7 @@ Each signature subpacket has a flag that indicates whether the subpacket is *cri
Since different OpenPGP implementations might support subsets of the standard, it would be fatal if, for example, an implementation did not understand the concept of signature expiration. Such an implementation would potentially accept an already expired signature. Since different OpenPGP implementations might support subsets of the standard, it would be fatal if, for example, an implementation did not understand the concept of signature expiration. Such an implementation would potentially accept an already expired signature.
By marking the expiration date subpacket as critical, the user can indicate that implementations that do not understand this type of subpacket are supposed to reject the signature as invalid. By marking the expiration date subpacket as critical, the user can indicate that implementations that do not understand this type of subpacket are supposed to reject the signature as invalid.
Sections 5.2.3.11 - 5.2.3.36 give guidance on which subpackets are usually marked as critical. RFC Sections [5.2.3.11](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-signature-creation-time) - [5.2.3.36](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-intended-recipient-fingerpr) give guidance on which subpackets are usually marked as critical.
## Advanced topics ## Advanced topics