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14th December 2013, 09:52 PM |#8  
pulser_g2's Avatar
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Originally Posted by Entropy512

Ok, that's useful.

I'll let pulser do final judgement on this. He's our resident tinfoilhatter. :P

Resident tinfoil hat responding to duty...

The issue I've seen with this system (and I must say, it is good that work is done on this, and I commend that it has been done) is the implementation.

Once again, a solution has been made, which is smart, has good features, but is crippled in the security area, due to making things "easy to use".

The specific issue is that, from what I can see, at least right now, there is no way to tell if a message is going to be sent encrypted or unencrypted. It's no good knowing AFTER the fact - you need to know before it is sent how it will be sent.

Additionally, if you are using encryption, from what I can see, the message is actually sent over the internet. This means there is a central repository of users stored on a server somewhere. That is centralisation, centralisation is bad... As I raised back at the time, there are side-information risks.

While the new implementation may well eliminate some of these, I am not convinced this system provides the level of anonymity that some may desire. My worry is that since the original idea was conceived, where a user's phone number being available to CM was not seen as a concern, that any solution has been architected without considering every aspect of security.

Securing correspondence via SMS would be very nice to have done properly. But this is simply a "hook", that takes what you *think* is an SMS, and sends it over the internet. There are plenty of people in the world (particularly developing nations), where they have poor, or limited, access to the internet. SMS can be a lifeline for them.

There are also many places (some incredibly large), which regularly and routinely block internet services they disagree with (not at all looking at China here...) - it is important that any system works worldwide, and is resistent to easy "blocking".

I would personally prefer to see the actual messages sent over SMS... That means if you have no internet connection, you can still send the SMS. And you can do so ENCRYPTED, rather than unencrypted.

At the end of the day though, until you can tell 100% whether something will be sent encrypted or unencrypted, you can't trust a system. The server operator may also gain useful metadata in this case (though not ideal, your carrier already gets metadata for SMS).

Tl;dr, it looks nice, but we need to look at everything here, and consider that not everyone has internet access all the time. After key-exchange is complete (I would like offline key exchange via NFC and QRcode (on the screen) as well, for in-person identity verification), we need to ensure that a user can securely communicate without internet connectivity.

Until then, this is just a smaller rival to iMessage. And hey, maybe that's a good thing... But for my money, it's not a secure SMS system...

Thoughts welcomed.
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