Mixmin encryption (who can see the cleartext?)

Ewald Böhm

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Sep 3, 2015, 7:26:02 AM9/3/15

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I'm confused about how mixmin encryption works.

Let's say there are just two different scenarios.
Who can see the cleartext in those two scenarios?

Scenario 1:
- I post, using Mixmin, from home, to a newsgroup.
Scenario 2:
- Same as above, but using a public vpn server.

In those two scenarios, who can "see" the cleartext of the
post?

Steve Crook

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Sep 3, 2015, 11:25:27 AM9/3/15

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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

On Thu, 3 Sep 2015 11:26:01 +0000 (UTC), Ewald Böhm wrote in
Message-Id: <ms9ao9$8bq$1...@news.mixmin.net>:

In both scenarios, everyone can see it as you're posting to a public
newsgroup.

If the server required authentication, the encrypted session would serve
to protect the login details. (Mixmin doesn't require authentication)

Encryption helps to hide who posts what. Your messages might be public
but you may prefer them not to be linked to you. This is a vague and
untrustable form of anonymity for various reasons. I can explain if you
would like more details.

In the case of Mixmin, it serves to hinder the spammers as only
encrypted users are allowed to post. For this reason, the average
spammer finds it easier to use Google. I'm very happy about that as
abuse complaints have to be addressed so the fewer I receive, the
happier I am.

I'm planning to drop the support for NNTPS soon as it's awkward running
a dedicated listener on a different port (563). This needs to be
started by root and doesn't get restarted along with the other server
components. This frequently causes me pain when upgrading. INN has
supported STARTTLS for a few years now so I'll probably stick with that.

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--
And with glasses high we raised a cry for freedom had arrived

Sir Gregory Hall, Esq.

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Sep 3, 2015, 2:02:08 PM9/3/15

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-----BEGIN PGP SIGNED MESSAGE-----
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You are so full of it, Steve! You make me laugh with your little
Usenet fetish.

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--

Sir Gregory

The Sorceress of Qar

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Sep 4, 2015, 10:35:16 AM9/4/15

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I use news.mixmin.net:563

Works great.

Keep up the good work, change whatever makes sense to change.

--
A Paradoxial World, for Sure.

Ewald Böhm

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Sep 15, 2015, 12:41:29 AM9/15/15

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On Thu, 03 Sep 2015 15:25:26 +0000, Steve Crook wrote:

> Encryption helps to hide who posts what. Your messages might be public
> but you may prefer them not to be linked to you. This is a vague and
> untrustable form of anonymity for various reasons. I can explain if you
> would like more details.

Hi Steve,
I just saw this, as I had a setup problem with my subscriptions.
Sorry I hadn't responded sooner.

I'm very confused, so, what I say below may be all wrong, but, it's
what I *thought* was the advantage of Mixmin over the others, but,
then, when I started thinking about it - I got confused.

1. I set up stunnel on my localhost & set up mixmin on my newsreader.
2. I sit at Starbucks & compose this message on my newsreader.
3. I hit "Send" and the cleartext is sent to the mixmin server.
4. If there was a login, it'd be encrypted, but you don't require a login.
5. Anyone at Starbucks & at its ISP can "see" the cleartext I just sent.
6. Your mixmin server then gives me a "posting-host" based on other
header information and my NNTP Posting Host IP address.
7. Anyone picking up your feed sees my cleartext & your hashed "posting-host".

Is that reasonably correct?
If so, why the need for stunnel?
Where's the encryption?

Steve Crook

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Sep 15, 2015, 4:05:28 AM9/15/15

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On Tue, 15 Sep 2015 04:41:29 +0000 (UTC), Ewald Böhm wrote in
Message-Id: <mt87ho$5iv$1...@news.mixmin.net>:

> On Thu, 03 Sep 2015 15:25:26 +0000, Steve Crook wrote:
>
>> Encryption helps to hide who posts what. Your messages might be public
>> but you may prefer them not to be linked to you. This is a vague and
>> untrustable form of anonymity for various reasons. I can explain if you
>> would like more details.
>
> Hi Steve,
> I just saw this, as I had a setup problem with my subscriptions.
> Sorry I hadn't responded sooner.
>
> I'm very confused, so, what I say below may be all wrong, but, it's
> what I *thought* was the advantage of Mixmin over the others, but,
> then, when I started thinking about it - I got confused.
>
> 1. I set up stunnel on my localhost & set up mixmin on my newsreader.
> 2. I sit at Starbucks & compose this message on my newsreader.
> 3. I hit "Send" and the cleartext is sent to the mixmin server.

At this point, your newsreader sends the cleartext to your local stunnel
that is masquarading as a newsserver. It encrypts your message and
sends it to Mixmin.

> 4. If there was a login, it'd be encrypted, but you don't require a login.
> 5. Anyone at Starbucks & at its ISP can "see" the cleartext I just sent.

No, they can only "see" the encrypted communication between your stunnel
and news.mixmin.net.

> 6. Your mixmin server then gives me a "posting-host" based on other
> header information and my NNTP Posting Host IP address.

Mixmin takes your IP address and salts it
(https://en.wikipedia.org/wiki/Salt_(cryptography)). The result is
SHA1 hashed and posted, as hex, in the posting-host field.

> 7. Anyone picking up your feed sees my cleartext & your hashed "posting-host".

Correct.

> Is that reasonably correct?
> If so, why the need for stunnel?
> Where's the encryption?

Hopefully I've explained those elements above. Let me know if it's not
clear and I'll try again.