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edit Public-Subkey packet

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Tammi L. Coles 2023-10-27 14:37:26 +02:00
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book/source/17-zoom_certificates.md
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@ -369,7 +369,7 @@ In the following sections,we make it easier for ourselves by directly examining
### Public-Subkey packet
First, we'll look at the *Public-Subkey packet* that contains the component key data of this subkey:
We'll now look at the *Public-Subkey packet* that contains the component key data of this subkey:
```text
$ sq packet dump --hex alice.pub-4--PublicSubkey
@ -392,11 +392,12 @@ Public-Subkey Packet, new CTB, 2 header bytes + 42 bytes
00000020 35 2a 46 01 f3 cc 00 f5 4a 09 3e 3f
```
Notice that the structure of this *Public-Subkey packet* is the same as the *Public-Key Packet* of the primary key, [above](public_key). Only the content of the two packets differs in some points:
Notice that the structure of this *Public-Subkey packet* mirrors the primary key's [*Public-Key packet*](public_key) above. However, there are notable differences between the two packets:
- The packet type ID (`CTB`) in this packet shows type 14 ([*Public-Subkey packet*](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-10.html#name-public-subkey-packet-tag-14)).
- The `pk_algo` value is set to `0x19` (decimal 25), which [corresponds to](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-10.html#name-public-key-algorithms) X25519. Note that even though both the primary key and this subkey use a cryptographic mechanism based on Curve25519, this encryption key uses Curve 25519 in a different way (X25519 is a Diffie–Hellman function built out of Curve25519).
- Accordingly, the public part of the cryptographic key pair is labeled with the corresponding name: `x25519_public` (however, note that this difference only reflects the semantics of the field, which is implied by the value of `pk_algo`. The actual data consists of just 32 bytes of cryptographic key material, without any type information.)
- The `pk_algo` value is set to `0x19` (decimal 25), which [corresponds to X25519](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-10.html#name-public-key-algorithms). Notably, though both the primary key and this subkey use a cryptographic mechanism based on Curve25519, the encryption key uses Curve 25519 in a different way: namely, X25519 is a Diffie–Hellman function constructed from Curve25519.
- Accordingly, the public part of the cryptographic key pair is labeled `x25519_public`, as implied by the value (`0x19`) of `pk_algo`. However, the actual data is just 32 bytes of cryptographic key material, without any type information.
### Subkey binding signature