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Clarify explanation of comparing fingerprints

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Andrew David Wong 2023-12-18 18:08:46 -08:00
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project-security/verifying-signatures.md
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@ -171,26 +171,61 @@ Fedora, `dnf install distribution-gpg-keys` will get you the QMSK along with
several other Qubes keys. On Debian, your keyring may already contain the
necessary keys.
Perhaps the most common route is to rely on the key's fingerprint. Every PGP
key has a fingerprint that uniquely identifies it among all PGP keys (viewable
with `gpg2 --fingerprint <KEY_ID>`). Therefore, if you know the genuine QMSK
Perhaps the most common route is to rely on the key's fingerprint, which is a
string of 40 alphanumeric characters, like this:
```
427F 11FD 0FAA 4B08 0123 F01C DDFA 1A3E 3687 9494
```
Every PGP key has one of these fingerprints, which uniquely identifies it among
all PGP keys. (On the command line, you can view a key's fingerprint with the
`gpg2 --fingerprint <KEY_ID>` command.) Therefore, if you know the genuine QMSK
fingerprint, then you always have an easy way to confirm whether any purported
copy of it is authentic, simply by comparing the fingerprints.
For example, here is the QMSK fingerprint:
```shell_session
pub 4096R/36879494 2010-04-01
Key fingerprint = 427F 11FD 0FAA 4B08 0123 F01C DDFA 1A3E 3687 9494
uid Qubes Master Signing Key
```
But how do you know that this is the real fingerprint? After all, [this website
But how do you know which fingerprint is the real one? After all, [this website
could be compromised](/faq/#should-i-trust-this-website), so the fingerprint
you see here may not be genuine. That's why we strongly suggest obtaining the
fingerprint from *multiple independent sources in several different ways*.
fingerprint from *multiple independent sources in several different ways*, then
comparing the strings of letters and numbers to make sure they match.
Here are some ideas for how to do that:
When it comes to PGP fingerprints, spaces and capitalization don't matter. In
other words, all of these fingerprints are considered the same:
```
427F 11FD 0FAA 4B08 0123 F01C DDFA 1A3E 3687 9494
427f 11fd 0faa 4b08 0123 f01c ddfa 1a3e 3687 9494
427F11FD0FAA4B080123F01CDDFA1A3E36879494
427f11fd0faa4b080123f01cddfa1a3e36879494
```
Instead, what matters is that *all* the characters are present in *exactly* the
same order. If even one character is different, the fingerprints do not match.
Even if two fingerprints have all the same characters, if any of those
characters are in a different order, sequence or position, then the
fingerprints do not match.
Note: You may sometimes see the entire fingerprint prefixed with `0x`, as in:
```
0x427F11FD0FAA4B080123F01CDDFA1A3E36879494
0x427f11fd0faa4b080123f01cddfa1a3e36879494
```
The `0x` prefix is sometimes used to indicate that the string following it is a
hexadecimal value, and some PGP-related tools may require this prefix. For the
purpose of comparing fingerprints as described here, you may safely ignore the
`0x` prefix, as it is not part of the fingerprint. As long as the 40-character
string after the `0x` matches exactly, the fingerprint is the same.
The general idea of "comparing fingerprints" is to go out into the world
(whether digitally, physically, or both) and find other 40-character strings
purporting to be the QMSK fingerprint, then compare them to your own purported
QMSK fingerprint to ensure that the sequence of alphanumeric characters is
exactly the same (again, regardless of spaces or capitalization). If any of the
characters do not match or are not in the same order, then at least one of the
fingerprints is a forgery. Here are some ideas to get you started:
- Check the fingerprint on various websites (e.g., [mailing
lists](https://groups.google.com/g/qubes-devel/c/RqR9WPxICwg/m/kaQwknZPDHkJ),
@ -204,10 +239,10 @@ Here are some ideas for how to do that:
talk](https://hyperelliptic.org/PSC/slides/psc2015_qubesos.pdf), on a
[T-shirt](https://twitter.com/legind/status/813847907858337793/photo/2), or
in the [recording of a presentation](https://youtu.be/S0TVw7U3MkE?t=2563)).
- Download old Qubes ISOs from different sources and check the included Qubes
Master Signing Key.
- Ask people to post the fingerprint on various mailing lists, forums, and chat
rooms.
- Download old Qubes ISOs from different sources and check the included Qubes
Master Signing Key.
- Repeat the above over Tor.
- Repeat the above over various VPNs and proxy servers.
- Repeat the above on different networks (work, school, internet cafe, etc.).
@ -215,11 +250,11 @@ Here are some ideas for how to do that:
confirm the fingerprint.
- Repeat the above from different computers and devices.
Once you've obtained the fingerprint from enough independent sources in enough
different ways that you feel confident that you know the genuine fingerprint,
keep it in a safe place. Every time you need to check whether a key claiming to
be the QMSK is authentic, compare that key's fingerprint to your trusted copy
and confirm they match.
Once you've observed enough matching fingerprints from enough independent
sources in enough different ways that you feel confident that you have the
genuine fingerprint, keep it in a safe place. Every time you need to check
whether a key claiming to be the QMSK is authentic, compare that key's
fingerprint to your trusted copy and confirm they match.
Now that you've imported the authentic QMSK, set its trust level to "ultimate"
so that it can be used to automatically verify all the keys signed by the QMSK