content-address hint? (was Re: intrinsic vs extrinsic identifier: toward more robustness?)

2023-10-04 Thread Simon Tournier 
Hi Ludo,

On Thu, 16 Mar 2023 at 18:45, Ludovic Courtès  wrote:

> Thanks for starting this discussion!

I feel this discussion is still pending, so I am resuming. :-)

If context is missing, the thread starts here.

    intrinsic vs extrinsic identifier: toward more robustness?
Simon Tournier 
Fri, 03 Mar 2023 19:07:23 +0100
id:87jzzxd7z8@gmail.com
https://lists.gnu.org/archive/html/guix-devel/2023-03
https://yhetil.org/guix/87jzzxd7z8@gmail.com


> Sources (fixed-output derivations) are already content-addressed, by
> definition (I prefer “content addressing” over “intrinsic
> identification” because that’s a more widely recognized term).

>From my understanding, this is correct only when the sources live in the
Guix project infrastructure.  I agree that if the source is
substitutable (= the source exists on one of substitute servers, i.e.,
Guix project servers), then the fixed-output derivation is
content-addressed,

For instance, let consider this fixed-output derivation:

--8<---cut here---start->8---
Derive
([("out","/gnu/store/n1k6jppyasn20zr6m8sfyv5ll07ibyf1-asciidoc-8.6.10.tar.gz","sha256","9e52f8578d891beaef25730a92a6e723596ddbd07bfe0d2a56486fcf63a0b983")]
 ,[]
 
,["/gnu/store/5iw2ivjw5njyyvi7avyphfcibgbqdbsc-mirrors","/gnu/store/vwyxp1dq4lb97n6b20w5cqxasy2dai79-content-addressed-mirrors"]
 ,"x86_64-linux","builtin:download",[]
 
,[("content-addressed-mirrors","/gnu/store/vwyxp1dq4lb97n6b20w5cqxasy2dai79-content-addressed-mirrors")
   ,("impureEnvVars","http_proxy https_proxy LC_ALL LC_MESSAGES LANG COLUMNS")
   ,("mirrors","/gnu/store/5iw2ivjw5njyyvi7avyphfcibgbqdbsc-mirrors")
   ,("out","/gnu/store/n1k6jppyasn20zr6m8sfyv5ll07ibyf1-asciidoc-8.6.10.tar.gz")
   ,("preferLocalBuild","1")
   ,("url","\"https://github.com/asciidoc/asciidoc/archive/8.6.10.tar.gz\";)])
--8<---cut here---end--->8---

I agree that the “url” field is useless while the content exists on the
“content-addressed-mirrors” list.  If one opens that file, then the code
reads:

--8<---cut here---start->8---
(begin
  (use-modules
   (guix base32))
  (define
(guix-publish host)
(lambda
(file algo hash)
  (string-append "https://; host "/file/" file "/"
 (symbol->string algo)
 "/"
 (bytevector->nix-base32-string hash
  (module-autoload!
   (current-module)
   (quote
(guix base16))
   (quote
(bytevector->base16-string)))
  (list
   (guix-publish "ci.guix.gnu.org")
   (lambda
   (file algo hash)
 (string-append "https://tarballs.nixos.org/;
(symbol->string algo)
"/"
(bytevector->nix-base32-string hash)))
   (lambda
   (file algo hash)
 (string-append "https://archive.softwareheritage.org/api/1/content/;
(symbol->string algo)
":"
(bytevector->base16-string hash)
"/raw/"
--8<---cut here---end--->8---

Therefore, the look-up is done with some content-addressed via these 3
servers.


> In a way, like Maxime way saying, the URL/URI is just a hint; what
> matters it the content hash that appears in the origin.

However, from my understanding, it is incorrect to speak about
content-addressed when the source (fixed-output derivation) does not
exist for whatever reason on any substitute servers.

The URL/URI is not “just a hint”.  It *is* the location from where the
data are fetched.  And it is not content-addressed.  If I am incorrect,
please could you explain?

Please note that if only one source is missing than all the castle falls
down.  Other said, robustness means the hunt of the corner cases. :-)

If I want to time-machine to d63ee94d63c667e0c63651d6b775460f4c67497d
from Sat Jan 4 2020, and need Git, then it fails because:

sha256 hash mismatch for 
/gnu/store/n1k6jppyasn20zr6m8sfyv5ll07ibyf1-asciidoc-8.6.10.tar.gz:
  expected hash: 10xrl1iwyvs8aqm0vzkvs3dnsn93wyk942kk4ppyl6w9imbzhlly
  actual hash:   1sh341j7ripkdb2wn6yf3rciln8ll89351b3d55gpkj89wypkmi2

Game over. )-:

Do we share the same understanding?


> What’s missing, both in SWH and in Guix, is the ability to store
> multiple hashes.  SWH could certainly store several hashes, computed
> using different serialization and hash algorithm combinations.

[...]

> The other option—storing multiple hashes for each origin in Guix—doesn’t
> sound practical:

Re: intrinsic vs extrinsic identifier: toward more robustness?

2023-04-06 Thread Simon Tournier 
Hi,

On jeu., 16 mars 2023 at 18:45, Ludovic Courtès  wrote:

>> For sure, we have to fix the holes and bugs. :-)  However, I am asking
>> what we could add for having more robustness on the long term.

> Sources (fixed-output derivations) are already content-addressed, by
> definition (I prefer “content addressing” over “intrinsic
> identification” because that’s a more widely recognized term).

This is the case when you consider that the result of the fixed-output
derivation is already inside the Guix “ecosystem”…

> In a way, like Maxime way saying, the URL/URI is just a hint; what
> matters it the content hash that appears in the origin.

…but else URL/URI is not just a “hint“.  Or could you explain what you
mean by a “hint”?

Maybe I misunderstand something, from my understanding, URL/URI is a
“hint” only when substitutes is available, else Guix relies on plain
URL/URI for fetching data.

--8<---cut here---start->8---
$ guix build hello -S --no-substitutes --check
The following derivation will be built:
  /gnu/store/3hxraqxb0zklq065zjrxcs199ynmvicy-hello-2.12.1.tar.gz.drv
building /gnu/store/3hxraqxb0zklq065zjrxcs199ynmvicy-hello-2.12.1.tar.gz.drv...

Starting download of 
/gnu/store/1s6xba6nafkxb242kafkg3x10jkdn2n9-hello-2.12.1.tar.gz
>From https://ftpmirror.gnu.org/gnu/hello/hello-2.12.1.tar.gz...
following redirection to 
`https://mirror.cyberbits.eu/gnu/hello/hello-2.12.1.tar.gz'...
downloading from https://ftpmirror.gnu.org/gnu/hello/hello-2.12.1.tar.gz ...

warning: rewriting hashes in 
`/gnu/store/3dq55rw99wdc4g4wblz7xikc8a2jy7a3-hello-2.12.1.tar.gz'; cross fingers
--8<---cut here---end--->8---

Other said, when speaking about robustness (broad meaning), I think we
cannot assume that the “content addressing” provided by the derivation,

--8<---cut here---start->8---
Derive
([("out","/gnu/store/3dq55rw99wdc4g4wblz7xikc8a2jy7a3-hello-2.12.1.tar.gz","sha256","8d99142afd92576f30b0cd7cb42a8dc6809998bc5d607d88761f512e26c7db20")]
 ,[]
 
,["/gnu/store/0mxnx8l4fgigvd7gakwdk6hc6im4wnai-disarchive-mirrors","/gnu/store/ckxc05iflc8jagdxwh4z1cxc23mb6i6q-mirrors","/gnu/store/wg1yp2vx8gb7qmcgyibqnwblahpp4bjg-content-addressed-mirrors"]
 ,"x86_64-linux","builtin:download",[]
 
,[("content-addressed-mirrors","/gnu/store/wg1yp2vx8gb7qmcgyibqnwblahpp4bjg-content-addressed-mirrors")
   
,("disarchive-mirrors","/gnu/store/0mxnx8l4fgigvd7gakwdk6hc6im4wnai-disarchive-mirrors")
   ,("impureEnvVars","http_proxy https_proxy LC_ALL LC_MESSAGES LANG COLUMNS")
   ,("mirrors","/gnu/store/ckxc05iflc8jagdxwh4z1cxc23mb6i6q-mirrors")
   ,("out","/gnu/store/3dq55rw99wdc4g4wblz7xikc8a2jy7a3-hello-2.12.1.tar.gz")
   ,("preferLocalBuild","1")
   ,("url","\"mirror://gnu/hello/hello-2.12.1.tar.gz\"")])
--8<---cut here---end--->8---

is still there and instead it would mean Guix has to rely on another
system (here ’url’).  Somehow, I am proposing to optionally add more
“content addressing” than the current NAR+SHA256 (and URL/URI) to then
be able to exploit other “content addressing“ systems.


> So it seems to me that the basics are already in place.

Well, there is two possible choices: (1) rely on an external service
that would be bridge the different content addressing systems (as
extending the Disarchive database or hope SWH will do it :-)) but this
other external service needs to be always available or (2) extend the
information of packages (optional fields, etc.).

Moreover about (1), all third-party channels would have to be ingested
by this external service.  About SWH, that’s possible.  About Disarchive
database, it would mean register this third-party channel or maintain
their own database.  Contrary to (2) where the identifier would be
optionally part of the package definition.


> What’s missing, both in SWH and in Guix, is the ability to store
> multiple hashes.  SWH could certainly store several hashes, computed
> using different serialization and hash algorithm combinations.

Please note that currently Guix relies on a “hint“ when SWH is used as
fallback.  For instance, consider most of the cases of git-fetch, Guix
provides to the SWH API the context (URL and Git tag) and let SWH
resolves in order to find the content addressing identifier.  It works
for many cases but it fails for history of history cases, e.g., when
upstream does in-place tag replacement.

And this strategy does not work with Subversion (svn-fetch) or Mercurial
(hg-fetch) or else.  It requires more work on our side (parse the result
of the query, extract relevant information etc.).  Nothing impossible
but far to be done, IMHO. :-)

Well, I still have mixed feelings about the SWH fallback robustness. :-)


> This is what you suggested at
> ; it was
> also discussed in the thread at
> .

Re: intrinsic vs extrinsic identifier: toward more robustness?

2023-03-16 Thread Ludovic Courtès 
Hi!

Thanks for starting this discussion!

Simon Tournier  skribis:

> For sure, we have to fix the holes and bugs. :-)  However, I am asking
> what we could add for having more robustness on the long term.
>
> It is not affordable, neither wanted, to switch from the current
> extrinsic identification to a complete intrinsic one.  Although it would
> fix many issues. ;-)

Sources (fixed-output derivations) are already content-addressed, by
definition (I prefer “content addressing” over “intrinsic
identification” because that’s a more widely recognized term).

In a way, like Maxime way saying, the URL/URI is just a hint; what
matters it the content hash that appears in the origin.

So it seems to me that the basics are already in place.

What’s missing, both in SWH and in Guix, is the ability to store
multiple hashes.  SWH could certainly store several hashes, computed
using different serialization and hash algorithm combinations.

This is what you suggested at
; it was
also discussed in the thread at
.  It
would be awesome if SWH would store Nar hashes; that would solve all our
problems, as you explained.

The other option—storing multiple hashes for each origin in Guix—doesn’t
sound practical: I can’t imagine packages storing and updating more than
one content hash per package.  That doesn’t sound reasonable.  Plus it
would be a long-term solution and wouldn’t help today.

Thoughts?

Ludo’.

Re: intrinsic vs extrinsic identifier: toward more robustness?

2023-03-07 Thread Simon Tournier 
Hi,

On Mon, 06 Mar 2023 at 13:22, Maxime Devos  wrote:

>>> For git-fetch, the value of the 'commit' field is intrinsic (except when
>>> it's a tag instead).
>> 
>> No, it is imprecise.  The exception is *not* label tag as value for the
>> ’commit’ field but the exception is Git commit hash as value.
>
> Are you referring to the fact that currently, the 'commit' field usually 
> contains a tag name, and that it containing a commit is the exception?

Yes.

> If so, that doesn't contradict my claim.

There is no contradiction but imprecision.


> I do not see how making a list of all identifiers helps with robustness 
> -- you need the object the identifiers point to, not the identifier itself.

If you have the identifiers, you have a chance to find again the
content.  For example, in addition to NAR+SHA256, we could also store
Git+SHA1 or plain SHA256 or something else.  It would help in exploiting
other content-address systems.  For instance, SWH stores,

"checksums": {
"sha1": "3a48fbd0a69c7875dc18bd48a16da04d1512ed47",
"sha1_git": "69cb76019a474330e99666f147ecb85e44de1ce6",
"sha256": 
"e62e0f13f9025642a52f9fcb12ca0c31d5e05f78e97224f55b3d70d47c73b549"
},

and maybe ’sha256_nar’ soon.  Somehow, we have a list of mirrors so why
not similarly having a list of intrinsic identifier.


> You are hashing the 'hello-2.12.1' directory

Thanks!  Having the noise too close and I missed the obvious. :-)


Cheers,
simon

Re: intrinsic vs extrinsic identifier: toward more robustness?

2023-03-06 Thread Maxime Devos 

Op 05-03-2023 om 21:21 schreef Simon Tournier:

Whatever the intrinsic identifier we consider – even ones based on very
weak cryptographic hash function as MD5, or based on non-crytographic
hash function as Pearson hashing, etc. – the integrity check is
currently done by SHA256.


How about using the hash of the integrity check as an intrinsic
identifier, like is done currently?  I mean, we hash it anyway with
sha256 for the integrity check anyway, might as reuse it.


Maybe ask GNUnet folk to address by NAR+SHA256 instead on their
specification. ;-)


Obviously, Guix should replace NAR+SHA256 by GNUnet FS URIs /j.


Kidding aside, your comment rises two points of view:

  1. Guix is fetching data from elsewhere and this elsewhere is not using
 NAR+SHAR256 intrinsic identifier.  Therefore, the question is how to
 adapt the source origin for taking into account this elsewhere?

  2. Replace the NAR+SHA256 integrity checksum by what content-addressed
 systems use as intrinsic identifier.  IMHO, that’s a bad idea for
 two reasons: (a) security, for instance SHA1 as used by SWH is not
 secure and (b) it will be unmanageable in practise.


I was thinking of (1), not (2).

All that’s said, Guix uses extrinsic identifiers for almost all origins,
if not all.  Even for ’git-fetch’ method.


For git-fetch, the value of the 'commit' field is intrinsic (except when
it's a tag instead).


No, it is imprecise.  The exception is *not* label tag as value for the
’commit’ field but the exception is Git commit hash as value.


Are you referring to the fact that currently, the 'commit' field usually 
contains a tag name, and that it containing a commit is the exception?

If so, that doesn't contradict my claim.


This can be solved by placing the actual commit in the 'commit' field of
git-reference, instead of the tag name, then things are completely
unambiguous -- this and its opposite were discussed in ‘On raw strings
in  commit field’ (*), IIRC.


The thread you are referencing [1] is based on misunderstandings.  I
would like to move forward, hence my detailed email. :-)

1: 



Your email is about intrinsic identifiers and more robustness, yet it 
doesn't mention using git commits more anywhere.  As such, I do not 
follow ‘hence my detailed email’ -- it contains detail, but it misses 
some relevant detail that I pointed out in my previous response.


Also, with ‘move forward’, do you mean ‘move forward’, or ‘maintain 
status quo’?  Because given that you are replying to the proposed 
solution (that even avoids problems pointed out in those threads) by 
saying nothing of technical importance and by pointing to some 
contentious things, it really appears the latter to me.



(*) Also maybe that thread about tricking peer review.

I didn't understand the position that commit field should contain the
(indirect, fragile) tag instead of the (direct, robust) commit, but
those differences could be sidestepped by having both a 'tag' field and
a 'commit' field, IIUC.


I would not frame this way.  My view is not to replace something by
something else, instead, is to add something and/or several things.


I was thinking of adding the commit (intrinsic) to the git-reference, 
instead of only having a tag (extrinsic) in the git-reference as is 
mostly done currently.


I also want to mention that, except of a general notion of 'more 
robustness' and a specific command "guix freeze -m manifest.scm" and 
such, you never mentioned what your view was, so I had to guess.



The problem then was to somehow map the NAR hash to the FS identifier.


Yes, that’s the problem. :-) GNUnet FS identifier is one case.  And my
discussion here is: could we augment source origin to be able to deal
with various identifier?



A straightforward solution would be to just replace the https:// by
gnunet:// in the origin (like in https://issues.guix.gnu.org/44199,
except that patch doesn't support fallbacks to other URLs like url-fetch
does).


Somehow, your proposition would be to have a list as URI, right?

  (origin
(method gnunet-fetch)
(uri
 (list
   (string-append "mirror://gnu/hello/hello-" version
".tar.gz")
   
"gnunet://fs/chk/TY48PGS5RVX643NT2B7GDNFCBT4DWG692PF4YNHERR96K6MSFRZ4ZWRPQ4KVKZV29MGRZTWAMY9ETTST4B6VFM47JR2JS5PWBTPVXB0.8A9HRYABJ7HDA7B0"
   "shw:1:dir:9c1eecffa866f7cb9ffdd56c32ad0cecb11fcf2a"
(file-name "gnunet-hello-2.10.tar.gz")
(sha256
 (base32
  "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i")


Yes, though in a proper version of 44199 (which doesn't exist yet) it 
would just be integrated into url-fetch instead of having a separate 
gnunet-fetch.



It is not affordable, neither wanted, to switch from the current
extrinsic identification to a complete intrinsic one.  Although it would
fix many issues. ;-)


How

Re: intrinsic vs extrinsic identifier: toward more robustness?

2023-03-05 Thread Simon Tournier 
Hi Maxime,

Thanks for your comments.

On Sat, 04 Mar 2023 at 01:08, Maxime Devos  wrote:

> To my understanding, there is only one 'real' identifier in Guix: the 
> (sha256sum (base32 ...)) (*).  Those other identifiers like the URL in 
> url-fetch and git-fetch are just hints on where to find the object -- 
> very important hints without which finding the object is much more 
> likely to fail, but just hints nonetheless.

I am not sure to understand why you mean by “hint”.  I would not call
URLs something like “just hints on where to find the object”.

NAR+SHA256 is only the ’real’ identifier when you allow
substitutes. Otherwise, Guix fetches using the ’uri’ from the field
’origin’.  And that’s the scenario I am envisioning here: for whatever
reasons, all the data in the stores Bordeaux and Berlin are gone, then
it is hard time for “guix time-machine”.


>> Intrinsic identifier also relies on a (trusted) map but collisions are
>> avoided as much as possible.  Somehow it strongly reduces the power of
>> the authority and it is often more robust.
>
> Who is 'the authority' here, how does the absence of collision reduces 
> the power of the authority, and what is your point about reducing the 
> power of the authority?

Considering intrinsic identifier, the “authority” is the data itself,
somehow.  In content-addressed systems, the “authority” is diluted or
absent.


>> Whatever the intrinsic identifier we consider – even ones based on very
>> weak cryptographic hash function as MD5, or based on non-crytographic
>> hash function as Pearson hashing, etc. – the integrity check is
>> currently done by SHA256.
>
> How about using the hash of the integrity check as an intrinsic 
> identifier, like is done currently?  I mean, we hash it anyway with 
> sha256 for the integrity check anyway, might as reuse it.

Maybe ask GNUnet folk to address by NAR+SHA256 instead on their
specification. ;-)

Kidding aside, your comment rises two points of view:

 1. Guix is fetching data from elsewhere and this elsewhere is not using
NAR+SHAR256 intrinsic identifier.  Therefore, the question is how to
adapt the source origin for taking into account this elsewhere?

 2. Replace the NAR+SHA256 integrity checksum by what content-addressed
systems use as intrinsic identifier.  IMHO, that’s a bad idea for
two reasons: (a) security, for instance SHA1 as used by SWH is not
secure and (b) it will be unmanageable in practise.


>> All that’s said, Guix uses extrinsic identifiers for almost all origins,
>> if not all.  Even for ’git-fetch’ method.
>
> For git-fetch, the value of the 'commit' field is intrinsic (except when 
> it's a tag instead).

No, it is imprecise.  The exception is *not* label tag as value for the
’commit’ field but the exception is Git commit hash as value.


> This can be solved by placing the actual commit in the 'commit' field of 
> git-reference, instead of the tag name, then things are completely 
> unambiguous -- this and its opposite were discussed in ‘On raw strings 
> in  commit field’ (*), IIRC.

The thread you are referencing [1] is based on misunderstandings.  I
would like to move forward, hence my detailed email. :-)

1: 



> (*) Also maybe that thread about tricking peer review.
>
> I didn't understand the position that commit field should contain the 
> (indirect, fragile) tag instead of the (direct, robust) commit, but 
> those differences could be sidestepped by having both a 'tag' field and 
> a 'commit' field, IIUC.

I would not frame this way.  My view is not to replace something by
something else, instead, is to add something and/or several things.


> The problem then was to somehow map the NAR hash to the FS identifier.

Yes, that’s the problem. :-) GNUnet FS identifier is one case.  And my
discussion here is: could we augment source origin to be able to deal
with various identifier?


> A straightforward solution would be to just replace the https:// by 
> gnunet:// in the origin (like in https://issues.guix.gnu.org/44199, 
> except that patch doesn't support fallbacks to other URLs like url-fetch 
> does).

Somehow, your proposition would be to have a list as URI, right?

 (origin
   (method gnunet-fetch)
   (uri
(list
  (string-append "mirror://gnu/hello/hello-" version
   ".tar.gz")
  
"gnunet://fs/chk/TY48PGS5RVX643NT2B7GDNFCBT4DWG692PF4YNHERR96K6MSFRZ4ZWRPQ4KVKZV29MGRZTWAMY9ETTST4B6VFM47JR2JS5PWBTPVXB0.8A9HRYABJ7HDA7B0"
  "shw:1:dir:9c1eecffa866f7cb9ffdd56c32ad0cecb11fcf2a"
   (file-name "gnunet-hello-2.10.tar.gz")
   (sha256
(base32
 "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i")



>> It is not affordable, neither wanted, to switch from the current
>> extrinsic identification to a complete intrinsic one.  Although it would
>> fix many issues. ;-)
>
> How about in-between: include

Re: intrinsic vs extrinsic identifier: toward more robustness?

2023-03-03 Thread Maxim Cournoyer 
Hi Maxime (it's been some time, welcome back!)

Maxime Devos  writes:

[...]

> I think nar stuff should be kept outside SWH.  It doesn't seem
> scalable to me for SWH to support the format of every distribution.
> Likewise, I think that SWH identifiers should _not_ become an
> intrinsic identifier that is recorded in package definitions -- if
> there are other archives that are somewhat SWH-like archives, then
> Guix should support them too even if they don't use SWH identifiers
> for whatever reason, and including the identifier of every single
> archive seems unscalable to me.
>
> I believe I have a solution on how to solve the ‘everyone uses
> different identifiers, how to map between them’ problem, but it will
> take some paragraphs:
>
> At some point in the past, when thinking about downloading source code
> over GNUnet File-sharing (FS), I had the problem that Guix and GNUnet
> uses different intrinsic identifiers -- Guix uses the NAR hash for
> querying substitute servers, whereas FS has a system of its own that's
> more convenient for P2P file-sharing stuff.
>
> The problem then was to somehow map the NAR hash to the FS identifier.
> I couldn't do this the Disarchive way, because the point was to be
> _P2P_ and Disarchive ... isn't.
>
> A straightforward solution would be to just replace the https:// by
> gnunet:// in the origin (like in https://issues.guix.gnu.org/44199,
> except that patch doesn't support fallbacks to other URLs like
> url-fetch does).
>
> The problem was that people demanded that gnunet:// should only be
> supported once there is actually source code on GNUnet and GNUnet is
> stable, but why would people put source code on GNUnet when no
> distribution supports it and how would GNUnet become stable without
> any users?
>
> To work-around these circular demands, I started 'rehash':
> 
> (current location: https://notabug.org/maximed/rehash).  It is a
> (P2P!) GNUnet service that maintains a 'SHA1512<->GNUnet FS URI'
> mapping, or more generally, a 'this hash type<->that hash type'
> mapping.
>
> (It is just a service on top of the DHT, so the same could easily be
> done for BitTorrent or IPFS.)
>
> It's rather incomplete at the moment (there is no verification or
> reputation mechanism at all so the network could be flooded with bogus
> mappings, mappings are only in DHT, not stored on disk, so they are
> lost on reboot, the POC Guix integretation is a bit limited), but the
> basics are there -- the POC successfully downloaded a substitute over
> GNUnet _without_ having to include FS URI in the narinfo (*)!.
>
> I'm writing about substitutes here, but the exact same approach could
> be done for plain source code.
>
> (*) I might have misremembered; I can't find the POC on
> issues.guix.gnu.org again, and I'm not sure if the POC used rehash or
> if it just included the FS URI in the narinfo.
>
> (TBC, I haven't been working on Rehash lately, but rather
> Scheme-GNUnet: a Scheme port of the GNUnet libraries that's less
> limited than Guile-GNUnet.  Idea is to make GNUnet-FS and rehash more
> convenient to use from Scheme, and in particular, in Guix.)

Thanks for sharing your efforts on the P2P in Guix/GNUnet front!  P2P
seems like it'd make substitutes mirroring easy and improve robustness
as the network gets populated.  It's very interesting; it'd definitely
make an interesting summer internship :-).

Keep up the good and inspiring hacks!

-- 
Thanks,
Maxim

Re: intrinsic vs extrinsic identifier: toward more robustness?

2023-03-03 Thread Maxime Devos 



Op 03-03-2023 om 19:07 schreef Simon Tournier:

Hi,

I would like to open a discussion about how we identify the source
origin (fixed output).  It is of vitally importance for being robust on
the long-term (say 3-5 years).  It matters in Reproducible Research
context, but not only.

# First thing first
===

## What is an intrinsic identifier or an extrinsic one?
===

  - extrinsic: use a register to keep the correspondence between the
identifier and the object; say label version as Git tag.

  - intrinsic: intimately bound to the designated object itself; say hash
as Git blob or tree and at some extent commit.

>
> [... some reordering for convenience of replying ...]
>
> Please note that the identification and the integrity is not the same.
> Since intrinsic identifier often uses cryptographic hash functions and
> integrity too, it is often confusing.

To my understanding, there is only one 'real' identifier in Guix: the 
(sha256sum (base32 ...)) (*).  Those other identifiers like the URL in 
url-fetch and git-fetch are just hints on where to find the object -- 
very important hints without which finding the object is much more 
likely to fail, but just hints nonetheless.


While identification and integrity might be different concepts, 
content-based identifiers like (sha256 (base32 ...)) accomplish both at 
the same time.


(*) FWIW, I would like to point out that Guix theoretically supports 
some other hashes as well, though they aren't used for any in-tree packages.



The register must be a trusted authority and it resolves by mapping the
key identifier to the object.  Having the object at hand does not give
any clue about the key identifier.  And collisions are very frequent;
two key identifiers resolve to the same content – hopefully! we call
that mirrors. ;-)


I first thought you where writing about 'extrinsic -> intrinsic (e.g. 
hash-based)' registers, so I was confused by your comment about 
collisions -- to my understanding, no sha256sum collisions are known. 
Going by your comment about mirrors, I think you meant an 'intrinsic -> 
extrinsic' map instead, e.g. 'sha256 -> a bunch of appropriate URLs'.



Intrinsic identifier also relies on a (trusted) map but collisions are
avoided as much as possible.  Somehow it strongly reduces the power of
the authority and it is often more robust.


Who is 'the authority' here, how does the absence of collision reduces 
the power of the authority, and what is your point about reducing the 
power of the authority?  I was thinking of ‘the authority=Guix package 
definition’, but then only the 'more robust' part of your conclusion 
makes sense to me.  Also, as you used 'but' instead of 'and', it appears 
you consider relying on a trusted map to be a bad thing, but that 
appears basic security and patch review to me.



Whatever the intrinsic identifier we consider – even ones based on very
weak cryptographic hash function as MD5, or based on non-crytographic
hash function as Pearson hashing, etc. – the integrity check is
currently done by SHA256.


How about using the hash of the integrity check as an intrinsic 
identifier, like is done currently?  I mean, we hash it anyway with 
sha256 for the integrity check anyway, might as reuse it.



## For example, consider this source origin,
==

 (source (origin
   (method url-fetch)
   (uri (string-append "mirror://gnu/hello/hello-" version
   ".tar.gz"))
   (sha256
(base32
 "086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd"

where ’mirror://gnu’ is resolved by Guix itself.  Or this one,

 (source
  (origin
(method git-fetch)
(uri (git-reference
  (url "https://github.com/FluxML/Zygote.jl;)
  (commit (string-append "v" version
(file-name (git-file-name name version))
(sha256
 (base32 "02bgj6m1j25sm3pa5sgmds706qpxk1qsbm0s2j3rjlrz9xn7glgk"

where Guix clones then checks out at the specification of the field
’commit’.

Here both are extrinsic identifiers.  For the first example, the register
is defined by ’%mirrors’.  For the second example, the register is the
folder ’.git/’.

Intrinsic identifier could be plain hash or hashed serialized data.
Using Guix b8f6ead:

--8<---cut here---start->8---
$ guix hash -S none -H sha256 -f nix-base32 -x $(guix build hello -S)
086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd

$ guix hash -S git -H sha256 -f nix-base32 -x $(guix build hello -S)
11kaw6m19rdj3d55y4cygk6k9zv6sn2iz4gpimx0j99ps87ij29l

$ guix hash -S nar -H sha256 -f nix-base32 -x 
/gnu/store/3dq55rw99wdc4g4wblz7xikc8a2jy7a3-hello-2.12.1.tar.gz
1lvqpbk2k1sb39z8jfxixf7p7v8sj4z6mmpa44nnmff3w1y6h8lh
--8<---cut here---end--->8---

Or some Git-like tree md5 of the

intrinsic vs extrinsic identifier: toward more robustness?

2023-03-03 Thread Simon Tournier 
Hi,

I would like to open a discussion about how we identify the source
origin (fixed output).  It is of vitally importance for being robust on
the long-term (say 3-5 years).  It matters in Reproducible Research
context, but not only.

# First thing first
===

## What is an intrinsic identifier or an extrinsic one?
===

 - extrinsic: use a register to keep the correspondence between the
   identifier and the object; say label version as Git tag.

 - intrinsic: intimately bound to the designated object itself; say hash
   as Git blob or tree and at some extent commit.

The register must be a trusted authority and it resolves by mapping the
key identifier to the object.  Having the object at hand does not give
any clue about the key identifier.  And collisions are very frequent;
two key identifiers resolve to the same content – hopefully! we call
that mirrors. ;-)

Intrinsic identifier also relies on a (trusted) map but collisions are
avoided as much as possible.  Somehow it strongly reduces the power of
the authority and it is often more robust.

Please note that the identification and the integrity is not the same.
Since intrinsic identifier often uses cryptographic hash functions and
integrity too, it is often confusing.

Whatever the intrinsic identifier we consider – even ones based on very
weak cryptographic hash function as MD5, or based on non-crytographic
hash function as Pearson hashing, etc. – the integrity check is
currently done by SHA256.

## For example, consider this source origin,
==

(source (origin
  (method url-fetch)
  (uri (string-append "mirror://gnu/hello/hello-" version
  ".tar.gz"))
  (sha256
   (base32
"086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd"

where ’mirror://gnu’ is resolved by Guix itself.  Or this one,

(source
 (origin
   (method git-fetch)
   (uri (git-reference
 (url "https://github.com/FluxML/Zygote.jl;)
 (commit (string-append "v" version
   (file-name (git-file-name name version))
   (sha256
(base32 "02bgj6m1j25sm3pa5sgmds706qpxk1qsbm0s2j3rjlrz9xn7glgk"

where Guix clones then checks out at the specification of the field
’commit’.

Here both are extrinsic identifiers.  For the first example, the register
is defined by ’%mirrors’.  For the second example, the register is the
folder ’.git/’.

Intrinsic identifier could be plain hash or hashed serialized data.
Using Guix b8f6ead:

--8<---cut here---start->8---
$ guix hash -S none -H sha256 -f nix-base32 -x $(guix build hello -S)
086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd

$ guix hash -S git -H sha256 -f nix-base32 -x $(guix build hello -S)
11kaw6m19rdj3d55y4cygk6k9zv6sn2iz4gpimx0j99ps87ij29l

$ guix hash -S nar -H sha256 -f nix-base32 -x 
/gnu/store/3dq55rw99wdc4g4wblz7xikc8a2jy7a3-hello-2.12.1.tar.gz
1lvqpbk2k1sb39z8jfxixf7p7v8sj4z6mmpa44nnmff3w1y6h8lh
--8<---cut here---end--->8---

Or some Git-like tree md5 of the decompressed data, e.g.,

--8<---cut here---start->8---
$ guix hash -S git -H md5 -f hex -x hello-2.12.1
3db60bcfecf17a5dd81e3fb5bfb1c191
--8<---cut here---end--->8---

Or some others.

--8<---cut here---start->8---
$ git clone https://github.com/FluxML/Zygote.jl
$ git -C Zygote.jl checkout v0.6.41

$ guix hash -S nar -H sha256 -f nix-base32 -x Zygote.jl
02bgj6m1j25sm3pa5sgmds706qpxk1qsbm0s2j3rjlrz9xn7glgk

$ guix hash -S git -H sha1 -f hex -x Zygote.jl
3cfdb31b517eec4173584fba2b1aa65daad46e09
--8<---cut here---end--->8---


# Second thing second
=

All that’s said, Guix uses extrinsic identifiers for almost all origins,
if not all.  Even for ’git-fetch’ method.

Consider that GitHub disappears and the default build farms ci.guix and
bordeaux.guix are unreachable for whatever reason.  Then Guix will
fallback to Software Heritage and will exploits its resolver.

--8<---cut here---start->8---
Initialized empty Git repository in 
/gnu/store/ns1f3b4wm5n470bczd2k5li6xpgbqkz7-julia-zygote-0.6.41-checkout/.git/
fatal: unable to access 'https://github.com/FluxML/Zygote.jl/': Could not 
resolve host: github.com
Failed to do a shallow fetch; retrying a full fetch...
fatal: unable to access 'https://github.com/FluxML/Zygote.jl/': Could not 
resolve host: github.com
git-fetch: 
'/gnu/store/55ba5ragbd5sd4r45n0q24vrxx9rigrm-git-minimal-2.39.1/bin/git fetch 
origin' failed with exit code 128
Trying content-addressed mirror at berlin.guix.gnu.org...
Trying content-addressed mirror at berlin.guix.gnu.org...
Trying to download from Software Heritage...
SWH: found revision