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Simplify "nesting" section

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Heiko Schaefer 2023-12-27 03:40:21 +01:00
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18
book/source/adv/signing_data.md
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@ -96,25 +96,19 @@ Important to note, the {term}`signer`'s {term}`public key<OpenPGP Certificate>`,
A {term}`one-pass signed message` can contain multiple signatures.
There are two subtly different use cases for this:
- Multiple signers can issue cryptographic signatures that can be stored in one shared (and thus space-efficient) inline signed message. In this case, each signer makes a cryptographic statement about just the signed message. The individual signatures are independent of each other.
- Alternatively, a later signer can sign not just the input message, but also include a previous signature in their signature. In this case, the second signer notarizes the previous signer's signature combined with the signed message.
```{note}
One-pass signatures are nested. The outermost one-pass signature packet corresponds to the outermost signature packet.
```
There is one exception, though.
```{note}
Of course there is.
```
There are two subtly different use cases for inline signatures that contain multiple signatures:
- Multiple signers can issue cryptographic signatures that can be stored in one shared (and thus space-efficient) inline signed message. In this case, each signer makes a cryptographic statement about just the signed message. The individual signatures are independent of each other.
- Alternatively, a later signer can sign not just the input message, but also include a previous signature in their signature. In this case, the second signer attests the previous signer's signature combined with the signed message.
To specify which of these two functions a signature performs, the {term}`one-pass signature packet` has a ["nested" flag](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#section-5.4-3.8.1), with a value of either `1` or `0`.
The OPS packet has a "nested" flag[^nested-flag], which can either be `1` or `0`.
If this flag is set to `0`, it indicates that further OPSs will follow this packet, which are calculated over the same plaintext data as this OPS is. A value of `1` indicates, that either no further OPS packets will follow (this OPS is the last), or that this OPS is calculated over the usual plaintext data, but wrapped inside any OPS+Signature combinations that follow this OPS.
[^nested-flag]: See [description of the nested flag](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#section-5.4-3.8.1).
This mechanism enables attested signatures, where the signer signs an already one-pass signed message including the already contained signature.
As a practical example, consider the following notation: