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Old 07-02-2012, 06:34 PM
 
Default TLS encrypted source for Debian iso signing keys?

Is there any TLS encrypted source for downloading the Debian iso signing
keys?

Of course, from a source verified by a common root certificate. Not from
the Debian CA, because there is no way to get this one from a trusted
source either, or is there?

If the answer is no, which were to correct component to file a bug
against?

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Old 07-02-2012, 08:06 PM
Roger Leigh
 
Default TLS encrypted source for Debian iso signing keys?

On Mon, Jul 02, 2012 at 11:34:15AM -0700, anotst01@fastmail.fm wrote:
> Is there any TLS encrypted source for downloading the Debian iso signing
> keys?
>
> Of course, from a source verified by a common root certificate. Not from
> the Debian CA, because there is no way to get this one from a trusted
> source either, or is there?

The ISO images, like the rest of the archive, are signed using
OpenPGP (GnuPG) signatures. You can obtain the signing key from
db.debian.org or the public keyservers.

> If the answer is no, which were to correct component to file a bug
> against?

None. The signing is rather more secure than what a TLS connection
would give you. It's signed by a number of Debian developers, and
backed by the entire web of trust (many thousands of signatures).
You don't need to download the signing (public) key securely in
order to validate that you have the correct one--it's not rooted
in a single place.

If you go and meet some developers and sign each other's keys, you
can be a part of this web of trust. i.e. trace the signature all
the way back to *your* key. This is real trust, based upon real
people trusting each other, rather than just having some purchased
certificate--how much trust do you place in one of those?


Regards,
Roger

--
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`. `' schroot and sbuild http://alioth.debian.org/projects/buildd-tools
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Old 07-02-2012, 08:49 PM
Jochen Spieker
 
Default TLS encrypted source for Debian iso signing keys?

anotst01@fastmail.fm:
>
> Is there any TLS encrypted source for downloading the Debian iso signing
> keys?

None that I know of, but I don't see a need for that either. Sure, you
could use one of the built-in certificates in your browser to bootstrap
the chain of trust to the signing keys. But that's not how PGP is
designed. If you don't own a PGP key that is somehow connected to the
Debian signing key, you can do something like this:

- Fetch the ISO + signature file (MD5SUMS, MD5SUMS.sign)
- Fetch the key used to sign the ISO and verify the signature
- See how this key is connected to other keys you may have reason to
trust (e.g. because you already have software installed that is signed
by a key that also signed the key used to sign the ISO)

The last step is a little awkward and unfortunately I didn't find a
(functional) web page that helps in tracking down trust paths easily.
The sites I found are either broken or use a hopelessly outdated key
set.

On the other hand, the model used by SSL/TLS depends on you trusting all
of the various, mostly unknown entities that somehow managed to have
their certificate shipped by your browser vendor. Remember that there's
no limit on which sites a certificate my sign. The past two years have
shown that this security model does not deserve as much trust as people
put into it.

> If the answer is no, which were to correct component to file a bug
> against?

If I were to file this bug I would report it against d-i. But I don't
think it will be solved in a satisfying way for you.

What I find more interesting is that the key 0x6294BE9B ("Debian CD
signing key") only has nine signatures and only one from someone using
his "official" @debian org address (0x3442684E, Steve McIntyre). That
could surely be improved. I am a little bit disappointed to learn that
even my fairly well-connected key doesn't help in finding a trust path
to the CD signing key.

J.
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Old 07-02-2012, 09:08 PM
 
Default TLS encrypted source for Debian iso signing keys?

I still do believe a TLS encrypted source to obtain the iso signing keys
is necessary.

What about the people who live many miles away from the next developer?
Someone living on an isle should take the next flight just to get the
gpg keys?

What about the people who are unable to meet with the next developer?
Example: Disabled ones or poor ones (journeys are expensive), etc...

The root CA's are not that bad. How many people do not get MITMed while
doing stuff like online banking... Scammers use (spear)fishing, breaks
in root CA's happen but are rare.

There are already free (as in free beer) root CA's (startssl). It won't
cost anything but requesting and installing the free certificate.
Without scarifying anything else.

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Old 07-02-2012, 09:37 PM
Roger Leigh
 
Default TLS encrypted source for Debian iso signing keys?

On Mon, Jul 02, 2012 at 10:49:14PM +0200, Jochen Spieker wrote:
> What I find more interesting is that the key 0x6294BE9B ("Debian CD
> signing key") only has nine signatures and only one from someone using
> his "official" @debian org address (0x3442684E, Steve McIntyre). That
> could surely be improved. I am a little bit disappointed to learn that
> even my fairly well-connected key doesn't help in finding a trust path
> to the CD signing key.

% gpg --list-sigs 6294BE9B
pub 4096R/6294BE9B 2011-01-05
uid Debian CD signing key <debian-cd@lists.debian.org>
sig 1B3045CE 2011-01-07 Colin Tuckley <colin@tuckley.org>
sig 3442684E 2011-01-05 Steve McIntyre <steve@einval.com>
sig A40F862E 2011-01-05 Neil McGovern <neil@halon.org.uk>
sig C542CD59 2011-01-05 Adam D. Barratt <adam@adam-barratt.org.uk>
sig 63C7CC90 2011-01-05 Simon McVittie <smcv@pseudorandom.co.uk>
sig 3 6294BE9B 2011-01-05 Debian CD signing key <debian-cd@lists.debian.org>
sub 4096R/11CD9819 2011-01-05
sig 6294BE9B 2011-01-05 Debian CD signing key <debian-cd@lists.debian.org>

All of the above named individuals are Debian developers. Note
that the UID shown is just one of several on their key:

% gpg --list-keys 1B3045CE 3442684E A40F862E C542CD59 63C7CC90
pub 1024D/1B3045CE 1999-07-09
uid Colin Tuckley <colin@tuckley.org>
uid [jpeg image of size 2652]
uid Colin Tuckley <colint@debian.org>
sub 2048g/5C5B9D12 1999-07-09

pub 4096R/3442684E 2009-05-09
uid Steve McIntyre <steve@einval.com>
uid Steve McIntyre <93sam@debian.org>
uid Steve McIntyre <stevem@chiark.greenend.org.uk>
sub 4096R/E2C26E29 2009-05-09

pub 4096R/A40F862E 2009-05-11
uid Neil McGovern <neil@halon.org.uk>
uid Neil McGovern <neilm@debian.org>
uid Neil McGovern <neil.mcgovern@collabora.com>
sub 4096R/B999855D 2009-05-11

pub 4096R/C542CD59 2009-07-11
uid Adam D. Barratt <adam@adam-barratt.org.uk>
uid Adam D. Barratt <adsb@debian.org>
uid Adam D. Barratt <adam@funky-badger.org>
sub 4096R/EC0E8DA0 2009-07-11

pub 4096R/63C7CC90 2009-05-08
uid Simon McVittie <smcv@pseudorandom.co.uk>
uid Simon McVittie <smcv@debian.org>
uid Simon James McVittie (born 1983-08-25)
uid Simon McVittie <simon.mcvittie@collabora.co.uk>
sub 4096R/20FB245D 2009-05-08 [expires: 2019-05-06]


Of these, I have signed Steve's key from when we met in Cambridge
earlier in the year, and I also signed Colin's new key (38C9D903)
but this isn't yet being used. So I am just two hops to the key
in the web of trust. I'm probably just another hop or two by
all the other keys, since I signed Adam and Simon's older keys,
and I also have lots of paths to the keys via other people's
keys. Even if I had never met any of these people personally,
I'd still only be three or four hops away.



Regards,
Roger

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Old 07-02-2012, 09:54 PM
Roger Leigh
 
Default TLS encrypted source for Debian iso signing keys?

On Mon, Jul 02, 2012 at 02:08:08PM -0700, anotst01@fastmail.fm wrote:
> I still do believe a TLS encrypted source to obtain the iso signing keys
> is necessary.

TLS encryption means that
- what travels over the connection is encrypted, and in theory only
decryptable at the two endpoints
- the identity of the endpoints are authenticated by possession of
certificates

Neither of these gives you any means of validating the provenance
of the data which you receive.

The GPG signatures let you validate that the content that you
downloaded has not been tampered with since it was signed and that
it is bit-for-bit identical with what the authors signed. But you
could download it from anywhere, even an untrusted source, and
still be able to validate that it was the genuine article.

> What about the people who live many miles away from the next developer?
> Someone living on an isle should take the next flight just to get the
> gpg keys?

No necessarily. Suppose you have a friend who has been to a
conference and exchanged signatures with the people he met there.
You can exchange signatures with your friend, and because you
trust him, you also trust the people he trusts. This is the
principle for how the web of trust operates.

But meeting people directly means you can place a higher level of
trust in them, so it is desirable to do so. I spent a day travelling
to Manchester from my home town to get my GPG key signed by a
Debian developer so I could initially join the project. And I
subsequetly built up a collection of many tens of signatures over
the course of a decade, mainly from UK developers, but also from
people in the US, Europe etc.

This is the point of the web of trust--it's strong because it's
based upon physical interaction with other people and validating
their identities. I can trust that this key is genuine because
I've met several people, who met other people, who met Steve,
Colin, Adam, etc., who then signed the archive signing key. That
is exceedingly difficult to fake.

> The root CA's are not that bad. How many people do not get MITMed while
> doing stuff like online banking... Scammers use (spear)fishing, breaks
> in root CA's happen but are rare.

As I said above, these are generally used to solve a different
problem. The actual ISO image is not signed with the certificate,
so the CA and TLS gives you nothing.

But (going off-topic), breaks in CAs do happen, and they issue
certificates to anyone who can pay, doing very little validation.
The security they provide is mostly illusory. If you could
download the signing keys over TLS, what would that *really*
mean? The answer is, outside the connection being encrypted,
not much, really.


Regards,
Roger

--
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`. `' schroot and sbuild http://alioth.debian.org/projects/buildd-tools
`- GPG Public Key F33D 281D 470A B443 6756 147C 07B3 C8BC 4083 E800


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Old 07-03-2012, 12:21 AM
 
Default TLS encrypted source for Debian iso signing keys?

Might work in your reality, but not in mine.

In fact I know no one who is using Debian. They rather stick with
pirated Windoze. Even Linux users are very rare. Even more rare are
people using encryption. None of them is using gpg.

>From my location I'd have to take a flight.

Posting gpg signing keys works for many other websites. How it works and
how I suggest...
- Go to https://some-project-website.com.
- Some root CA vouches for the identity of some-project-website.com.
- The author posts his gpg public key (fingerprint) somewhere on
https://some-project-website.com.
- The root CA proofes that the gpg public key belongs to the admin of
some-project-website.com. (Possible breach in server security or root
CA.)
- The fingerprint was authenticated over SSL and at least the root CA
vouched for it, better than no one.
- Download the software.
- Download the hash.
- Gpg verifiy the hash.
- Compare the has with the software.

Agreed, that's not safe as gpg but it's still safer than no verification
at all.

For demonstration some imaginative values...
Probability, that
- download without any verification and attacker inserts a backdoor =
0,01 %
- download gpg key over SSL (root CA), gpg verify, root CA gets broken
and attacker inserts a backdoor = 0,001 %
- using gpg web of trust properly, someone found a flaw (zero day, no
one told about) in gpg, can impersonate any signature and attacker
inserts a backdoor = 0,0001 %.

There can no perfect security. There can be no guarantees. You can only
higher the effort for an attacker to break the system.

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Old 07-03-2012, 08:02 AM
Jochen Spieker
 
Default TLS encrypted source for Debian iso signing keys?

Roger Leigh:
> On Mon, Jul 02, 2012 at 10:49:14PM +0200, Jochen Spieker wrote:
>> What I find more interesting is that the key 0x6294BE9B ("Debian CD
>> signing key") only has nine signatures and only one from someone using
>> his "official" @debian org address (0x3442684E, Steve McIntyre). That
>> could surely be improved. I am a little bit disappointed to learn that
>> even my fairly well-connected key doesn't help in finding a trust path
>> to the CD signing key.
>
-- snip
> All of the above named individuals are Debian developers. Note
> that the UID shown is just one of several on their key:

Ah, thanks, I overlooked that. I didn't recognize any names apart from
Steve and Neil. My fault.

I only (knowingly) signed one DD's key (AC583520) and that doesn't help
veryfing the CD signing key:

$ gpg --verify --max-cert-depth 10 MD5SUMS.sign
gpg: Signature made Sun 13 May 2012 02:02:13 PM CEST using RSA key ID 6294BE9B
gpg: Good signature from "Debian CD signing key <debian-cd@lists.debian.org>"
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
Primary key fingerprint: DF9B 9C49 EAA9 2984 3258 9D76 DA87 E80D 6294 BE9B

BTW, does gpg offer any way to find a trust path between two keys in my
key ring?

J.
--
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Old 07-03-2012, 01:59 PM
Camaleón
 
Default TLS encrypted source for Debian iso signing keys?

On Mon, 02 Jul 2012 11:34:15 -0700, anotst01 wrote:

> Is there any TLS encrypted source for downloading the Debian iso signing
> keys?

(...)

There's apt-secure:

http://wiki.debian.org/SecureApt

But beyond that, I'm not aware of any TLS/SSL implementation.

What kind of benefit do you foresee for an encrypted channel to get the
keys? They are public :-?

> If the answer is no, which were to correct component to file a bug
> against?

You can suggest that feature by opening a wishlist bug report in the BTS,
component "general" or maybe "ftp.debian.org", but don't bother about it,
it'll be changed as required.

Greetings,

--
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Old 07-03-2012, 08:54 PM
Rob Owens
 
Default TLS encrypted source for Debian iso signing keys?

On Mon, Jul 02, 2012 at 11:34:15AM -0700, anotst01@fastmail.fm wrote:
> Is there any TLS encrypted source for downloading the Debian iso signing
> keys?
>
> Of course, from a source verified by a common root certificate. Not from
> the Debian CA, because there is no way to get this one from a trusted
> source either, or is there?
>
> If the answer is no, which were to correct component to file a bug
> against?
>
I agree with the OP that it is not necessarily easy to become a part of
the greater GPG / Debian web of trust. As a simple Debian user and
administrator, I have never had the occasion to meet a Debian developer
in person.

A while back I started a thread about how to properly verify the Lenny
iso, which Steve McIntyre helped me out with.
http://lists.debian.org/debian-user/2010/07/msg00492.html

Basically you can use the debian-keyring package to obtain keys of many
Debian developers. You can have a high level of trust that those keys
are real because the package is signed and apt-get would notify you if
the signature was not real. The iso you are downloading should be
signed by someone in that keyring.

-Rob


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