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Re: purpose of InRelease in apt [was: non-GPG signatures; was: Rust requirements]

From Simon McVittie <smcv@debian.org>
Newsgroups linux.debian.devel
Subject Re: purpose of InRelease in apt [was: non-GPG signatures; was: Rust requirements]
Date 2025-11-10 17:10 +0100
Message-ID <LPCCR-bWGa-11@gated-at.bofh.it> (permalink)
References (5 earlier) <LMCJ3-9S05-3@gated-at.bofh.it> <LPkmC-bJVj-13@gated-at.bofh.it> <LPlC2-bKHO-13@gated-at.bofh.it> <LPqs1-bO9i-1@gated-at.bofh.it> <LPxMR-bT3e-1@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Mon, 10 Nov 2025 at 11:51:38 +0100, Simon Josefsson wrote:
>- Nice to have: don't add round-trip latency fetching multiple files.
>  This one argues for putting everyhing in one file, such as extending
>  InRelease.

My understanding is that this is not actually the purpose of InRelease, 
although it's a desirable side-effect. Instead, the point of InRelease 
is that if the top-level metadata (Release file) is served in the same 
file as its signatures and during the same http transaction, then it 
cannot possibly be inconsistent, even during a mirror resync - whereas 
for Release and Release.gpg (or Release.sigstore, or whatever other 
signature format you might want to use), when mirroring Debian onto 
commodity web servers with unspecifed cache lifetimes or downloading 
through a caching proxy with cache behaviour similarly outside our 
control, there would often a window during which your mirror serves the 
old Release but the new Release.gpg, or vice versa. The result is that 
`apt update` fails with signature verification errors, even when you are 
not actually under attack. That's harmful from the point of view of 
getting updated software promptly, and also from the point of view of 
detecting attacks.

For the rest of the tree, a new enough version of apt can download 
Packages, Sources, etc. from sha256sum-based paths (content-addressed 
storage), so mirrors can provide continuity by offering both the old and 
the new Packages files under their hash-based names for a while; and the 
actual packages (.deb, .dsc, etc.) have uniquely versioned filenames, so 
they do not have the same update atomicity concerns as the metadata. The 
InRelease file is the only one that apt needs to be able to download 
from a hard-coded path, because apt can't know what hash to expect, and 
then that provides the "map" for downloading the rest.

If I remember correctly, Flatpak has a similar design where the signed 
"summary" (its equivalent of the InRelease file) is the only hard-coded 
filename, and is served as a single blob containing both content and 
signature, for much the same reason as apt's InRelease; and then 
everything else is downloaded from a sha256-based content-addressed 
filename, so that tampering by a malicious intermediary is easy to 
detect, and accidental mismatches on a non-malicious mirror are not 
possible.

     smcv

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Hard Rust requirements from May onward Julian Andres Klode <jak@debian.org> - 2025-10-31 21:50 +0100
  Re: Hard Rust requirements from May onward John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> - 2025-10-31 22:40 +0100
    Re: Hard Rust requirements from May onward Simon Richter <sjr@debian.org> - 2025-11-01 04:20 +0100
      Re: Hard Rust requirements from May onward Geert Stappers <stappers@stappers.nl> - 2025-11-01 08:40 +0100
        Re: Hard Rust requirements from May onward Bjørn Mork <bjorn@mork.no> - 2025-11-01 13:40 +0100
          Re: Hard Rust requirements from May onward Simon Josefsson <simon@josefsson.org> - 2025-11-01 14:40 +0100
            Re: Hard Rust requirements from May onward Andrey Rakhmatullin <wrar@debian.org> - 2025-11-01 15:40 +0100
              Re: Hard Rust requirements from May onward Simon Josefsson <simon@josefsson.org> - 2025-11-01 20:40 +0100
                Re: Hard Rust requirements from May onward Philipp Kern <pkern@debian.org> - 2025-11-01 21:10 +0100
                Re: Hard Rust requirements from May onward Holger Levsen <holger@layer-acht.org> - 2025-11-02 00:20 +0100
                Re: Hard Rust requirements from May onward Simon Josefsson <simon@josefsson.org> - 2025-11-02 10:30 +0100
                Re: Hard Rust requirements from May onward Simon Josefsson <simon@josefsson.org> - 2025-11-02 10:40 +0100
                Re: Hard Rust requirements from May onward Philipp Kern <pkern@debian.org> - 2025-11-09 21:40 +0100
                Re: Hard Rust requirements from May onward Simon Josefsson <simon@josefsson.org> - 2025-11-09 23:00 +0100
                Re: Hard Rust requirements from May onward Philipp Kern <phil@philkern.de> - 2025-11-09 23:30 +0100
                Re: Hard Rust requirements from May onward Simon Josefsson <simon@josefsson.org> - 2025-11-10 11:40 +0100
                Re: Hard Rust requirements from May onward Andrey Rakhmatullin <wrar@debian.org> - 2025-11-10 12:20 +0100
                Re: Hard Rust requirements from May onward Holger Levsen <holger@layer-acht.org> - 2025-11-10 13:40 +0100
                Re: Hard Rust requirements from May onward Simon Richter <sjr@debian.org> - 2025-11-10 04:10 +0100
                Re: Hard Rust requirements from May onward Simon Josefsson <simon@josefsson.org> - 2025-11-10 12:00 +0100
                Re: Hard Rust requirements from May onward Simon Richter <sjr@debian.org> - 2025-11-10 15:00 +0100
                Re: Hard Rust requirements from May onward David Kalnischkies <david@kalnischkies.de> - 2025-11-10 17:50 +0100
                Re: Hard Rust requirements from May onward Simon Josefsson <simon@josefsson.org> - 2025-11-10 20:20 +0100
                Re: Hard Rust requirements from May onward Simon Josefsson <simon@josefsson.org> - 2025-11-10 20:30 +0100
                Re: purpose of InRelease in apt [was: non-GPG signatures; was: Rust  requirements] Simon McVittie <smcv@debian.org> - 2025-11-10 17:10 +0100
                Re: purpose of InRelease in apt [was: non-GPG signatures; was: Rust  requirements] Stefano Rivera <stefanor@debian.org> - 2025-11-13 13:20 +0100
                Re: purpose of InRelease in apt [was: non-GPG signatures; was: Rust  requirements] Simon Josefsson <simon@josefsson.org> - 2025-11-13 18:20 +0100
          Re: Hard Rust requirements from May onward Russ Allbery <rra@debian.org> - 2025-11-01 17:50 +0100
          Re: Hard Rust requirements from May onward Christoph Biedl <debian.axhn@manchmal.in-ulm.de> - 2025-11-05 09:10 +0100
        Re: Re: Hard Rust requirements from May onward John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> - 2025-11-02 11:20 +0100
    Re: Hard Rust requirements from May onward Antoni Boucher <bouanto@zoho.com> - 2025-11-01 16:30 +0100
      Re: Hard Rust requirements from May onward John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> - 2025-11-02 11:50 +0100
        Re: Hard Rust requirements from May onward Antoni Boucher <bouanto@zoho.com> - 2025-11-02 16:30 +0100
  Re: Hard Rust requirements from May onward Julian Andres Klode <jak@debian.org> - 2025-10-31 22:50 +0100
  Re: Hard Rust requirements from May onward Paul Tagliamonte <paultag@debian.org> - 2025-11-01 15:20 +0100
    Re: Hard Rust requirements from May onward Paul Tagliamonte <paultag@debian.org> - 2025-11-01 15:20 +0100
    Re: Re: Hard Rust requirements from May onward John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> - 2025-11-02 11:30 +0100
    Re: Hard Rust requirements from May onward Bill Allombert <ballombe@debian.org> - 2025-11-02 15:40 +0100
  Re: Hard Rust requirements from May onward Joerg Jaspert <joerg@debian.org> - 2025-11-02 13:10 +0100
    Re: Hard Rust requirements from May onward Richard Lewis <richard.lewis.debian@googlemail.com> - 2025-11-02 16:20 +0100
      Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-02 18:10 +0100
    Re: Hard Rust requirements from May onward Julian Andres Klode <jak@debian.org> - 2025-11-02 17:30 +0100
      Re: Hard Rust requirements from May onward Joerg Jaspert <joerg@debian.org> - 2025-11-02 17:40 +0100
    Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-03 23:20 +0100
      Re: Hard Rust requirements from May onward Ansgar 🙀 <ansgar@debian.org> - 2025-11-04 07:30 +0100
        Re: Hard Rust requirements from May onward Mike Hommey <mh@glandium.org> - 2025-11-04 08:10 +0100
        Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-04 11:50 +0100
          Re: Hard Rust requirements from May onward Simon Richter <sjr@debian.org> - 2025-11-04 12:10 +0100
            Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-04 13:30 +0100
              Vendoring Simon Richter <sjr@debian.org> - 2025-11-04 13:50 +0100
          Re: Hard Rust requirements from May onward Holger Levsen <holger@layer-acht.org> - 2025-11-04 13:20 +0100
            Re: Hard Rust requirements from May onward Simon Richter <sjr@debian.org> - 2025-11-04 13:30 +0100
            Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-04 16:00 +0100
              Re: Hard Rust requirements from May onward Holger Levsen <holger@layer-acht.org> - 2025-11-04 16:50 +0100
                Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-04 19:40 +0100
        Re: Hard Rust requirements from May onward Stephan Verbücheln <verbuecheln@posteo.de> - 2025-11-04 15:30 +0100
          Re: Hard Rust requirements from May onward Fabian Grünbichler <debian@fabian.gruenbichler.email> - 2025-11-04 18:40 +0100
      Re: Hard Rust requirements from May onward Fabian Grünbichler <debian@fabian.gruenbichler.email> - 2025-11-04 18:30 +0100
        Re: Hard Rust requirements from May onward Sebastian Ramacher <sramacher@debian.org> - 2025-11-04 19:10 +0100
          Re: Hard Rust requirements from May onward Fabian Grünbichler <debian@fabian.gruenbichler.email> - 2025-11-04 19:40 +0100
        Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-04 20:10 +0100
          Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-04 21:50 +0100
          Re: Hard Rust requirements from May onward Fabian Grünbichler <debian@fabian.gruenbichler.email> - 2025-11-05 07:50 +0100
            Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-05 12:10 +0100
        Re: Hard Rust requirements from May onward Adrian Bunk <bunk@debian.org> - 2025-11-05 18:40 +0100
        Re: Hard Rust requirements from May onward Philipp Kern <pkern@debian.org> - 2025-11-06 22:10 +0100
    Re: Hard Rust requirements from May onward Sean Whitton <spwhitton@spwhitton.name> - 2025-11-05 16:00 +0100
  Re: Hard Rust requirements from May onward David Kalnischkies <david@kalnischkies.de> - 2025-11-03 13:40 +0100
    apt-ftparchive alternatives (was: Hard Rust requirements from May  onward) Jeremy Stanley <fungi@yuggoth.org> - 2025-11-03 19:00 +0100
      Re: apt-ftparchive alternatives (was: Hard Rust requirements from  May onward) nick black <dankamongmen@gmail.com> - 2025-11-03 19:50 +0100
        Re: apt-ftparchive alternatives (was: Hard Rust requirements from  May onward) Jeremy Stanley <fungi@yuggoth.org> - 2025-11-03 20:00 +0100
          Re: apt-ftparchive alternatives (was: Hard Rust requirements from  May onward) Peter Pentchev <roam@ringlet.net> - 2025-11-03 21:00 +0100
          Re: apt-ftparchive alternatives Richard Lewis <richard.lewis.debian@googlemail.com> - 2025-11-15 14:00 +0100
      Re: apt-ftparchive alternatives (was: Hard Rust requirements from  May onward) David Kalnischkies <david@kalnischkies.de> - 2025-11-05 16:10 +0100
        Re: apt-ftparchive alternatives Ahmad Khalifa <ahmad@khalifa.ws> - 2025-11-06 22:20 +0100
          Re: apt-ftparchive alternatives David Kalnischkies <david@kalnischkies.de> - 2025-11-09 17:00 +0100
            Re: apt-ftparchive alternatives Ahmad Khalifa <ahmad@khalifa.ws> - 2025-11-09 21:50 +0100
              Re: apt-ftparchive alternatives David Kalnischkies <david@kalnischkies.de> - 2025-11-10 14:00 +0100

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