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XMPP: The secure communication protocol that respects privacy

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Re: XMPP: The secure communication protocol that respects privacy

#61

Post by zaik »

infosechandbook wrote: post #54
jmnicolas wrote: post #43

Earlier quoted context omitted.

Thanks for the laugh, you should write news title it would be fun! Anyway the problem of Signal is that you have to use your phone number and a phone number is a much stronger link to you than an ip for example. As the ex boss of NSA said "We Kill People Based on Metadata".

> Anyway the problem of Signal is that you have to use your phone number and a phone number is a much stronger link to you than an ip for example. Signal requires access to a valid phone number during registration, not "your phone number." It can even be a virtual/landline/temporary phone number without any SIM cards or cell phones involved. How is this a "much stronger link to you than an ip"? And how about looking…

> It can even be a virtual/landline/temporary phone number without any SIM cards or cell phones involved.

Then contact discovery would not work, which is the main advantage of collecting the phone number in the first place. How many of your contacts who use Signal used their real phone number?

> XMPP servers are a gold mine when it comes to metadata.

Then even more so for Signal, since metadata for all users can be collected by a single entity. This is not possible in a federated network like XMPP.

Re: XMPP: The secure communication protocol that respects privacy

#62

Post by zaik »

tialaramex wrote: post #55
jmnicolas wrote: post #43

Earlier quoted context omitted.

Thanks for the laugh, you should write news title it would be fun! Anyway the problem of Signal is that you have to use your phone number and a phone number is a much stronger link to you than an ip for example. As the ex boss of NSA said "We Kill People Based on Metadata".

But I already have a phone number. My friends already know my phone number. If I instead got a "nickname" it would be tialaramex of course, which is even more identifying than my phone number. If I chose a deliberate random pseudonymous "nickname" to avoid "metadata" - then nobody can contact me, what use is that? The NSA may "kill people based on metadata" but XMPP produces far more metadata for such decisions than…

> Remember, when my friend Steve sent me a Signal message last week, Signal does not know who sent that.

This seems wrong. How could the Signal server have relayed the message from Steve to you if it does not know the recipient?

Re: XMPP: The secure communication protocol that respects privacy

#63

Post by infosechandbook »

zaik wrote: post #56
infosechandbook wrote: post #49

Earlier quoted context omitted.

> How should that be possible if OMEMO is enabled (which is the default in more modern clients)? See https://infosec-handbook.eu/articles/xmpp-aitm/#t5 TL;DR: XMPP clients can't distinguish between legitimate and injected messages, even if OMEMO is enabled. The XMPP client just displays injected messages as an unencrypted message from the sender.

In Conversations unauthenticated messages are displayed with a red background, whereas OMEMO authenticated messages are displayed in green. They do not look the same.

Nobody claimed that they look the same.

As mentioned in the linked article, the behavior upon receiving an injected message is client specific. In any way, the injected message is somehow presented to the (non-technical) user who might then be targeted. We all know the same problem exists in the e-mail world.

Re: XMPP: The secure communication protocol that respects privacy

#64

Post by infosechandbook »

zaik wrote: post #53
infosechandbook wrote: post #28

The article describes XMPP as "secure" by highlighting TLS (protecting data in transit only) and experimental OMEMO (protecting a small part of an XMPP message only if enabled and working). What about other crucial security features, see https://www.eff.org/deeplinks/2018/03/building-secure-messen... ? Then, XMPP is described as "privacy respecting" mostly because you can use a nickname instead of a phone number for…

You mention IP address, location based on IP addresses, timestamps, bytes transmitted and number of packets as metadata which is disclosed to the server admin. What alternative messenger do you suggest which does not disclose this metadata to the server operator?

> disclosed to the server admin

Please read the article before and after these items. The first finding isn't about the server admin but about external parties such as law enforcement (not the user, not the admin). The reason for this finding: Some people claim XMPP traffic can't be censored as nobody can identify XMPP traffic from outside. This isn't true as this finding shows. You can easily detect and filter XMPP coming through network devices.

This finding might be the most unsurprising one in the article from a technical perspective, and we are well aware of this.

Re: XMPP: The secure communication protocol that respects privacy

#65

Post by f1refly »

tialaramex wrote: post #47
southerntofu wrote: post #38

Earlier quoted context omitted.

If you care to elaborate, i'm sure that'll be of interest to maintainers. Although to be fair Pidgin doesn't exactly have the reputation to be maintained (despite recent efforts to start again) so i would strongly recommend to try again without that specific client in the equation.

> Although to be fair Pidgin doesn't exactly have the reputation to be maintained (despite recent efforts to start again) so i would strongly recommend to try again without that specific client in the equation. Quality of Implementation matters. If Pidgin "doesn't exactly have the reputation" and yet it's still notionally part of your ecosystem, then your whole ecosystem doesn't exactly deserve the reputation you tho…

Since there is nothing one can do to identify a specific client, you cannot just block them. If they violate the spec that should be reason enough to consider them not real clients. I personally have no experience with pidgin and xmpp, but I can recommend https://dino.im for linux. It uses omemo by default and works like a charm.

Re: XMPP: The secure communication protocol that respects privacy

#66

Post by infosechandbook »

zaik wrote: post #61
infosechandbook wrote: post #54

Earlier quoted context omitted.

> Anyway the problem of Signal is that you have to use your phone number and a phone number is a much stronger link to you than an ip for example. Signal requires access to a valid phone number during registration, not "your phone number." It can even be a virtual/landline/temporary phone number without any SIM cards or cell phones involved. How is this a "much stronger link to you than an ip"? And how about looking…

> It can even be a virtual/landline/temporary phone number without any SIM cards or cell phones involved. Then contact discovery would not work, which is the main advantage of collecting the phone number in the first place. How many of your contacts who use Signal used their real phone number? > XMPP servers are a gold mine when it comes to metadata. Then even more so for Signal, since metadata for all users can be c…

> How many of your contacts who use Signal used their real phone number?

Most of them; however, there is no obligation to provide any personal data when registering a SIM card in my country. Even if providing personal data would be mandatory and if we assume that telcom providers track us all the time, then it doesn't mean that this data is accessible to the organization behind an instant messaging service.

> Then even more so for Signal, since metadata for all users can be collected by a single entity. This is not possible in a federated network like XMPP.

This ignores that Signal and XMPP don't process the same amount of metadata in the first place, and the de-facto centralization of the XMPP network (also stated in our article -> the majority of XMPP users only uses a small number of public XMPP instances, and these XMPP instances are hosted by a tiny number of companies in mainly three countries on this planet).

Re: XMPP: The secure communication protocol that respects privacy

#67

Post by ezst »

goodpoint wrote: post #52
southerntofu wrote: post #40

Earlier quoted context omitted.

What would be your alternative? I agree there's a lot to research and improve in the XMPP ecosystem ( see also https://joinjabber.org/faqs/security/ ) but "admin in the middle" is not exactly a bug but a property of federated systems. If your alternative is to use a centralized platform (which potentially requires a phone number to sign on) that's a trade-off i'm not willing to make. I'm personally very happy with my…

XMPP leaks less metadata than alternative like Matrix, but it still very vulnerable to traffic correlation attacks from an external observer, server compromise and malicious server admin. Far from ideal. Briar mitigates[1] these risks by using p2p messaging over Onion Services. [1] mitigates: it's well known that even Tor cannot protect from correlation attack from a global observer but mounting such attack requires…

tor isn't perfect, but if that's good-enough for your use-case, you can use/host a server over it: https://gist.github.com/dllud/a46d4a555e31dfeff6ad41dcf20729...

Re: XMPP: The secure communication protocol that respects privacy

#68

Post by MattJ100 »

zaik wrote: post #62
tialaramex wrote: post #55

Earlier quoted context omitted.

But I already have a phone number. My friends already know my phone number. If I instead got a "nickname" it would be tialaramex of course, which is even more identifying than my phone number. If I chose a deliberate random pseudonymous "nickname" to avoid "metadata" - then nobody can contact me, what use is that? The NSA may "kill people based on metadata" but XMPP produces far more metadata for such decisions than…

> Remember, when my friend Steve sent me a Signal message last week, Signal does not know who sent that. This seems wrong. How could the Signal server have relayed the message from Steve to you if it does not know the recipient?

They have a feature called "sealed sender"[1]. Your Signal client authenticates to a Signal service that verifies you, and then signs and issues a certificate that you can use to vouch for your identity.

Then, you can encrypt this certificate as part of your message. Then ask Signal to deliver your message to the recipient. The Signal server won't be able to tell the recipient the account that the message is from, but after the recipient decrypts the message they will see the signed certificate and know it was you.

The problem with this is, Signal is centralized and they see the both the IP address (and other metadata) when you contact them to obtain the certificate and they they also see the IP address you send the message from. Correlation between the two Signal-operated services would reveal your identity. Unfortunately we, as users, have no way to know that this is not happening.

[1]: https://signal.org/blog/sealed-sender/

Re: XMPP: The secure communication protocol that respects privacy

#69

Post by f1refly »

ddtaylor wrote: post #58
f1refly wrote: post #16

Earlier quoted context omitted.

Security is always a tradeoff with convenience. How should a "per user" verification work in your opinion? A single master key that signs subkeys? Would the master key be secured with yet another password? What happens with already signed keys if a user loses access to the master key? Will I have to explain to my auntie over the phone that her master key password is somehow different to her account password and that…

That sounds significantly more complex and worse than how Matrix just works out of the box.

Omemo just works out of the box as well. You don't have to check the key fingerprints, noone forces you to. For people who aren't interested the chat opens and they can start writing and sending, the encryption is completely transparent.

Re: XMPP: The secure communication protocol that respects privacy

#70

Post by rakoo »

zaik wrote: post #62
tialaramex wrote: post #55

Earlier quoted context omitted.

But I already have a phone number. My friends already know my phone number. If I instead got a "nickname" it would be tialaramex of course, which is even more identifying than my phone number. If I chose a deliberate random pseudonymous "nickname" to avoid "metadata" - then nobody can contact me, what use is that? The NSA may "kill people based on metadata" but XMPP produces far more metadata for such decisions than…

> Remember, when my friend Steve sent me a Signal message last week, Signal does not know who sent that. This seems wrong. How could the Signal server have relayed the message from Steve to you if it does not know the recipient?

At the time of reception, the Signal server knew that there was a message from a certain IP to a certain recipient. If the message was put in the queue, the originating IP was forgotten. Once the message is delivered, the recipient is forgotten.

EDIT: Signal can totally be used through Tor, so the IP can be hidden from Signal. As neighbor comments have said it still knows at that moment that a message from you is sent.

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