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In the current year, I guess the answer is simply "use Signal". I'm not sure I understand why it's so important that it has to be an actual phone call, even for
by hnarn 7y ago
In the current year, I guess the answer is simply "use Signal". I'm not sure I understand why it's so important that it has to be an actual phone call, even for a thought experiment, i.e. it has to go over the phone network to a device with a phone number. If that is the case in any real scenario, it seems a reasonable guess that it's because one or two parties are somehow restricted from using other channels -- and if so, is there any reason to believe that this restriction would not in itself make it simpler to monitor that restricted party, and therefore less secure?
- 4bpp 7y agoEven if Signal's assertion that they do not keep metadata is in fact trustworthy, a network-scale adversary (such as a nation-state) could easily figure out that you called someone and who you called by looking at the data exchanged between your phone (which they know) and the Signal servers, and looking what other connections started and ended at the same time as yours and had a similar bandwidth usage profile. (How many Signal phone calls are even started in any given short window of time, like 1 second?)
- close04 7y agoPerhaps this would be another way to obfuscate the collection of metadata with techniques similar to anti-fingerprinting in Tor. An app like Signal could sync the time across all parties and send/receive all data in predetermined packet sizes and at predetermined delivery times across vast enough segments of their network. This would in theory make it a lot harder to infer who are the partners in a specific conversation based on timestamps and traffic volume. The mechanism for picking the interval and packet size is debatable as long as the entropy of these values is low enough (does not allow for uniquely identifiable values). Maybe randomly from a list of predetermined values, taking into account some priority you set in advance, the size of the message, or the network conditions. If every client/server on the network sent and received the data in synced identically looking bursts it might raise the bar for successful metadata analysis. Any chance Signal or any other app already do this?
- gruez 7y agoIs approach is going to kill battery life because the phone has to be always online to receive those times transmission.
- ghostpepper 7y agoMost modern CPUs/SoCs spend most of their time (ideally) asleep or trying to go to sleep, and then waking at predefined intervals to transmit data. As long as this interval could be synchronized to some multiple of the transmission interval I don't think this would negatively impact battery life.
- pmoriarty 7y agoThe techniques you're talking about, and others, have also been used in anonymous remailers[1] to resist traffic analysis[2]. The mixminion[3] remailer design document[4] goes in to details on those mitigations. Of course, real time conversations require certain constraints that email messages don't have, so some of the mitigations techniques used in remailers might not be practical here. Signal's designers must have been well aware of Tor and anonymous remailers, so if traffic analysis mitigation techniques were not used by Signal it was a deliberate design decision on their part. [1] - https://en.wikipedia.org/wiki/Anonymous_remailer https://en.wikipedia.org/wiki/Anonymous_remailer [2] - https://en.wikipedia.org/wiki/Traffic_analysis https://en.wikipedia.org/wiki/Traffic_analysis [3] - https://en.wikipedia.org/wiki/Mixminion https://en.wikipedia.org/wiki/Mixminion [4] - https://www.mixminion.net/minion-design.pdf https://www.mixminion.net/minion-design.pdf
- deugtniet 7y agoCorrect me if I'm wrong, but I believe the signal servers are hosted on google cloud, using encrypted traffic to obfuscate the point of exit for a signal user. This is why in the past, governments were unable to block signal without blocking google or all google cloud customers themselves.
- hnarn 7y agoIf they know about your physical device you are in a bad situation, but you would be in a worse situation if you used a phone line that they knew about. If we're moving the goal posts then yes, there are many ways to compromise a connection, but in no situation can I see that it would be beneficial to use a landline or a regular cellphone over a smartphone with the ability to encrypt and authenticate. So why is the question how to "make a secret phone call" if a phone call is an inferior technology to begin with? If the threshold for usage was high and required specialized technical knowledge, then sure, but you can hardly say that about Signal or VPN applications.
- upofadown 7y agoSignal runs off your phone number. So the problem would reduce to the one solved in the article at some level.
- jmg2 7y agoYou make your call on a phone that's on the local PD's imsi catching mitm? because that's what, would happen in London...