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edit ch7 cleartext signature

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book/source/07-signing_data.md
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@ -87,14 +87,14 @@ Important to note, the signer's public key, critical for the final verification
### Cleartext signatures
The *Cleartext Signature Framework* (CSF) is an OpenPGP mechanism that combines two goals:
The *Cleartext Signature Framework* (CSF) in OpenPGP accomplishes two primary objectives:
- It leaves the message in clear text format, so that it can be viewed directly by a human in a program that knows nothing about OpenPGP.
- At the same time, it adds an OpenPGP signature that allows verification of that message by users whose software supports OpenPGP.
- maintaining the message in a human-readable cleartext format, accessible without OpenPGP-specific software
- incorporating an OpenPGP signature for authentication by users with OpenPGP-compatible software
#### Example
In {numref}`cleartext` we inspect an example of a cleartext signature in detail. Let's have a brief look at this example, here, to get a sense of what a cleartext signature looks like:
Below is a detailed example of a {numref}`cleartext` signature:
```text
-----BEGIN PGP SIGNED MESSAGE-----
@ -111,15 +111,11 @@ r13/eqMN8kfCDw==
-----END PGP SIGNATURE-----
```
The cleartext signature consists of two blocks, which contain the message and a signature, respectively. In this case, the message consists of the text "hello world".
This signature is split into two parts: a message ("hello world") and an ASCII-armored OpenPGP signature. The message is immediately comprehensible to a human reader, while the signature block allows for the message's authenticity verification via OpenPGP software.
Notice that this message is readable by a human reader, without requiring additional software tools, as long as the reader understands which elements to ignore.
#### Use case
The message is followed by a block that contains an ASCII-armored OpenPGP signature for the message. Using this signature, OpenPGP software can verify the authenticity of the message in the first block.
#### Use-case
One use-case for cleartext signatures is: Asking someone to sign some piece of data. The person who is asked to sign the data can easily inspect it with simple commandline tools, such as `cat`, and verify that they agree with the data they are asked to sign.
A common use case is requesting someone to sign data. The signer can easily inspect the data using simple command line tools (e.g., `cat`) to verify that they agree with the content of the data before deciding to sign it.
```{admonition} TODO
:class: warning
@ -139,14 +135,10 @@ explain text transformations for cleartext signatures (LF->CRLF and additional e
#### Pitfalls
Cleartext signatures are popular and have useful applications.
At the same time, they are considered a "legacy method"[^csf-gnupg] by some.
While widely used, cleartext signatures are sometimes considered a "legacy method"[^csf-gnupg]. The RFC outlines [pitfalls of cleartext signatures](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-issues-with-the-cleartext-s) and advises that inline and detached signature forms are often preferable.
[^csf-gnupg]: https://lists.gnupg.org/pipermail/gnupg-devel/2023-November/035428.html
The RFC points out a number of specific [pitfalls of cleartext signatures](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-issues-with-the-cleartext-s), and how to avoid them. It advises that in many cases, the inline and detached signature forms are preferable.
## Advanced topics
### Nesting of one-pass signatures