From: ludo@gnu.org (Ludovic Courtès)
To: Nikita Karetnikov <nikita@karetnikov.org>
Cc: guix-devel@gnu.org
Subject: Re: Signed archives (preliminary patch)
Date: Fri, 28 Feb 2014 23:05:02 +0100 [thread overview]
Message-ID: <87ob1qyju9.fsf@gnu.org> (raw)
In-Reply-To: <87a9dbj5km.fsf@karetnikov.org> (Nikita Karetnikov's message of "Sat, 01 Mar 2014 01:22:17 +0400")
Nikita Karetnikov <nikita@karetnikov.org> skribis:
>> There’s an important check missing here: the code verifies that BODY* is
>> a valid signature, but it doesn’t check whether what it signs
>> corresponds to this narinfo up to but excluding the ‘Signature’ field.
>
> Oh, indeed.
>
>> 5. pass the hash to the signature verification procedure.
>
> Then, it should extract the other hash from the Signature line, compare
> the hashes, and run the rest of the checks, right?
The signature is computed over a hash of the narinfo up to the Signature
line, not included.
So the substituter must keep a string containing said lines, and compute
the hash of the UTF-8/ASCII representation of this string.
Then, for verification purposes, it must make sure that the hash found
in the signature sexp is the same as the hash computed as above.
>>> + ("Signature" . ,(lambda (narinfo)
>>> + (let ((sig (narinfo-signature narinfo)))
>>> + (string-append
>>> + (number->string (signature-version sig))
>>> + ";"
>>> + (signature-key-id sig)
>>> + ";"
>>> + (base64-encode
>>> + ;; XXX: Can we assume UTF-8 here?
>>> + (string->utf8
>>> + (canonical-sexp->string
>>> + (signature-body sig)))))))))
>
>> It’s important to keep the original signatures intact.
>
> Not sure I follow. Can I simply use ("Signature" . ,narinfo-signature)?
>
>> To fix this, the <narinfo> record must include an additional field to
>> contain the original narinfo string.
>
> Please elaborate. Which string are you talking about?
The narinfo.
Suppose the signature is computed over a hash of this:
--8<---------------cut here---------------start------------->8---
StorePath: /nix/store/phw82pzgl32ygpaa1z2v3l04afni7f28-gdbm-1.10
URL: nar/phw82pzgl32ygpaa1z2v3l04afni7f28-gdbm-1.10
Compression: bzip2
NarHash: sha256:1mn4rm7gs71dsqdm1gilw3h3krgfgbjsmni9yz9dziw1jpcrk3x1
NarSize: 372720
References: 9fnjjsbarscbmakr44ixfv9yhg6z12mw-glibc-2.17 lwc6sygaglzfk17v3w15cc2xv97fjgci-gcc-4.7.2 phw82pzgl32ygpaa1z2v3l04afni7f28-gdbm-1.10
Deriver: ykf90hcbvn3nm9ai7ikpw992vdq6l95k-gdbm-1.10.drv
System: x86_64-linux
--8<---------------cut here---------------end--------------->8---
The following narinfo, although semantically equivalent, would fail
signature verification:
--8<---------------cut here---------------start------------->8---
NarSize: 372720
StorePath: /nix/store/phw82pzgl32ygpaa1z2v3l04afni7f28-gdbm-1.10
References: 9fnjjsbarscbmakr44ixfv9yhg6z12mw-glibc-2.17 lwc6sygaglzfk17v3w15cc2xv97fjgci-gcc-4.7.2 phw82pzgl32ygpaa1z2v3l04afni7f28-gdbm-1.10
Deriver: ykf90hcbvn3nm9ai7ikpw992vdq6l95k-gdbm-1.10.drv
System: x86_64-linux
URL: nar/phw82pzgl32ygpaa1z2v3l04afni7f28-gdbm-1.10
NarHash: sha256:1mn4rm7gs71dsqdm1gilw3h3krgfgbjsmni9yz9dziw1jpcrk3x1
Compression: bzip2
--8<---------------cut here---------------end--------------->8---
That’s why the <narinfo> must include a copy of the exact textual
representation of the narinfo that was signed. Then, ‘write-narinfo’
must simply write out that string, unchanged (including the ‘Signature’
line.)
HTH,
Ludo’.
next prev parent reply other threads:[~2014-02-28 22:05 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-26 14:13 ‘guix archive’ doesn’t work over ‘./pre-inst-env’ Nikita Karetnikov
2014-01-26 14:52 ` Ludovic Courtès
2014-01-26 16:09 ` Signed archives (was: ‘guix archive’ doesn’t work over ‘./pre-inst-env’) Nikita Karetnikov
2014-01-26 19:36 ` Signed archives Ludovic Courtès
2014-01-27 15:36 ` Nikita Karetnikov
2014-01-27 15:56 ` Ludovic Courtès
2014-02-03 10:45 ` Nikita Karetnikov
2014-02-04 13:12 ` Ludovic Courtès
2014-02-20 9:54 ` Nikita Karetnikov
2014-02-21 21:17 ` Ludovic Courtès
2014-02-27 20:48 ` Signed archives (preliminary patch) Nikita Karetnikov
2014-02-27 22:43 ` Ludovic Courtès
2014-02-28 9:21 ` Mark H Weaver
2014-02-28 10:37 ` Ludovic Courtès
2014-02-28 18:46 ` Nikita Karetnikov
2014-02-28 21:22 ` Nikita Karetnikov
2014-02-28 22:05 ` Ludovic Courtès [this message]
2014-03-03 22:54 ` Nikita Karetnikov
2014-03-04 21:59 ` Ludovic Courtès
2014-03-08 22:38 ` Nikita Karetnikov
2014-03-08 22:46 ` Nikita Karetnikov
2014-03-09 17:22 ` Ludovic Courtès
2014-03-09 22:35 ` Ludovic Courtès
2014-03-11 9:51 ` Nikita Karetnikov
2014-03-12 11:57 ` Nikita Karetnikov
2014-03-12 14:25 ` Ludovic Courtès
2014-03-12 23:37 ` [PATCH 2/2] guix substitute-binary: Support the Signature field of a narinfo file. (was: Signed archives (preliminary patch)) Nikita Karetnikov
2014-03-13 21:38 ` [PATCH 2/2] guix substitute-binary: Support the Signature field of a narinfo file Ludovic Courtès
2014-03-13 21:55 ` Nikita Karetnikov
2014-03-13 22:53 ` Ludovic Courtès
2014-03-15 12:24 ` Nikita Karetnikov
2014-03-31 21:54 ` Signed archives (preliminary patch) Ludovic Courtès
2014-02-21 22:10 ` Applying the GPG web-of-trust to Guix (was Re: Signed archives) Mark H Weaver
2014-02-21 23:10 ` Ludovic Courtès
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