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According to Edward Snowden in this tweet...

Phones used in real-world ops are disposed on a per-action, or per-call basis. Lifetimes of minutes, hours. Not days.

Let's imagine for a moment that I'm Jason Bourne. I've stopped by the kiosk in Waterloo Station and picked up a PAYG mobile phone. Presumably I've used fake ID.

At the same time, my counterparty Jack Bauer is picking up a prepaid phone from a similar kiosk at Los Angeles International Airport.

How do I actually place a call to him, given that both of us have new phone numbers?

curiousdannii
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Roger Lipscombe
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  • Comments are not for extended discussion; this conversation has been [moved to chat](http://chat.stackexchange.com/rooms/37469/discussion-on-question-by-roger-lipscombe-how-would-two-people-with-burner-phone). – Rory Alsop Mar 24 '16 at 16:48

12 Answers12

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Burner phone numbers as an OTP 'equivalent'

You can think of the "identities" of those phones (phone number, SIM, phone itself/IMEI) as an equivalent of one-time pad encryption - you exchange the phone numbers (multiple) over a secure channel - e.g., when meeting in person; and then they're secure and provide no useful information (for network/metadata analysis) as long as you discard them after a single use.

In your proposed scenario, Jack would have picked up a bunch of prepaid phone cards and given you the list of those numbers. Afterwards, if you'd need to contact him, you would call the first number on the list, have your conversation, and after that you could both discard the phones. If you'd expect a future call, then you'd turn on the phones corresponding to the second item on your lists.

Peteris
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    For most 'ops' this is likely the situation. Your average Bourne isn't likely to just go off and do some spy stuff, things will be planned ahead of time. That planning will involve previsions for communications – Jay Mar 21 '16 at 07:50
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    Something that just occurred to me while reading this answer: what if some clever person at a three-letter agency that has access to phone metadata in whatever country our spies are operating in creates a simple tool that can search through that metadata and find the numbers of phones that have been used only once during some period of time where'd you expect almost all "real" (ie. non-burner) recently assigned numbers to be used more than that? Better yet, what if that tool could identify calls where used-once phone number called another used-once number? – mostlyinformed Mar 21 '16 at 20:40
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    @halfinformed the usual goal of phone call metadata analysis is to link a particular phone to (other) real world people. For example, a phone found on a suspect can allow to identify other suspected numbers called from it, and identify them as they eventually link to "common" people by call metadata. Calls on such 'burner' numbers would be suspicious and identifiable, but in the absence of other data (e.g. interception and recording of the call) it gives no link to your identities iff they are single-use only - when the authorities have the suspect numbers, they are already trashed. – Peteris Mar 21 '16 at 20:48
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    I suppose one thing you could do live, if you were in both providers' systems, is to detect *and intercept* burner-burner calls, by detecting all calls that are the first ever use of the numbers at both ends. You'd get some false positives, of course, but it must be a fairly rare event that the first thing a person does with a new mobile is call another brand new mobile. Then if Jack and Jason are aware of such a system, they could call one from a list of popular numbers (e.g. customer service and information lines), before making the real call, to throw off this simple analysis. – Steve Jessop Mar 22 '16 at 15:28
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    @SteveJessop in essence it means that burner phones provide security in an environment where intercepting and recording calls requires e.g. obtaining a warrant beforehand, and are vulnerable (or require extra encryption for the actual call) in a legal environment where "record everything and sort out legal issues afterwards" is acceptable. – Peteris Mar 22 '16 at 15:31
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    @Peteris: agreed, if all calls are intercepted and recorded, then any call that can later be identified as suspicious on the basis of its metadata, must be assumed to be eventually listened to by your opponents. I just speculate here that there could exist an intermediate legal (or storage-space) environment, where you want to avoid your call being *immediately* suspicious such that it can be intercepted on the fly, but it's not so bad for it to be observable later as suspicious in hindsight, because by then the chance to intercept is past. – Steve Jessop Mar 22 '16 at 15:34
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    ... oh, and this can also emerge naturally even in the "record everything" environment if there's a time limit on the usefulness of the information in the call. Once you're past the end of the movie there's no value in figuring out, "aaaah, Bourne made this call to Bauer from Waterloo, and agreed to meet at Harrods". Because the massive shoot-out at Harrods in act two already established that ;-) Whereas if they agree to a murder then the call might constitute evidence they can't *ever* afford to be found, in which case mass interception and recording stops them using unencrypted burners. – Steve Jessop Mar 22 '16 at 15:37
  • @Steve Jessop [late reply] But what if you take an approach where you use "burner" status of the phones involved to help prioritize which calls out of a set you to listen to? Let's take an all too concrete & realistic example: an intelligence agency that doesn't much care about Belgium privacy law has the technical capacity to intercept & record virtually every phone call that is made to/from the terrorist-plagued Molenbeek district of Brussels. But even an NSA or a GCHQ probably doesn't have enough translators/analysts to have actual humans listen to more than small fraction of them... – mostlyinformed Mar 26 '16 at 04:08
  • ...in any timely manner. But what if said agency used a scoring system to "rank" calls for priority of human processing, and such a system were designed to give high priority to (among other factors) calls made from a number with little or no call history *to* a number with little or no call history. Or, to go back to our Jack/Jason scenario, ranking burner phone calls in a broader area (say, a certain broad metropolitan area) but adding an additional narrowing factor (like, perhaps, where a computer has determined that both speakers on a call are likely adult males) to aid prioritization. – mostlyinformed Mar 26 '16 at 04:32
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If you know Jack

A few weeks or months before the call, you could create a simple web page with a login wall and a signup page. In order to sign up, you need to write your phone number. By using standard measures, you can hide your access to the website, hide as much as possible the website in the deep web and protect the database.

You now need to tell Jack the URL: this can be done in different ways, including using a standard dead drop or - if you are Jason Bourne, it should be a piece of cake- by breaking into Jack's house and putting pieces of paper with the URL in the pockets of every trouser,jacket,etc. he uses (obviously the pieces of paper must not be handwritten, and you must check the absence of watermarks on the paper, so to avoid identification of the printer).

At this point, you and Jack separately buy your burner phones. Jack uses an open wifi network to access the website and write his phone number in the database. At a given time, you log in, retrieve the number from the website and write it. The website can be built in such a way to delete its content after been accessed twice. You are now ready to call Jack.

The tricky part is guaranteeing that the other phone number written in the database is actually Jack's and not Mike's (Adm. Michael S. Rogers). This can be achieved by agreeing codewords to be used at the beginning of the phone call (which can be written on the above-mentioned pieces of paper).

EDIT

Jeff Meden suggested the possibility of a man in the middle attack. Basically, the scheme outlined doesn't prevent Mike from replacing the number entered by Jake with his own number and setting up a relay to forward calls to Jake's burner phone. In this way, Mike could be able to listen the conversation between Jason and Jack.

This attack could be thwarted (thanks again to Jeff!) by encrypting the data entered in the database (in this case, Jack's number) with a pad written on the pieces of paper planted on Jack.

Of course, if a history mechanism doesn't exist, Mike could arbitrarily alter the ciphertext, knowing that if the corresponding plaintext is not a valid phone number, the call will not take place.

A. Darwin
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  • To verify it is actually his number in the database you could include some sort of predetermined passphrase at the login wall. Such as name: Marty McFly, phone: Burner number, Message: My Mom Made Me Make More Mayonnaise. So all random passerbys and counter spies that don't include that message are flagged as not Jack. – DasBeasto Mar 21 '16 at 12:53
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    Predetermined codewords used at the beginning of the call wouldn't protect you against a man-in-the-middle attack. – ChrisInEdmonton Mar 21 '16 at 13:32
  • @ChrisInEdmonton I know, but I neglected the possibility of MitM attack, because the attacker cannot associate Jason and Jack to the two phones and, lacking any kind of suspect, I doubt that a MitM attack would be mounted on random phones. – A. Darwin Mar 21 '16 at 14:00
  • Why ignore the MitM but still think a codeword scheme is useful? If Mike did want to know what you two had to say, he would check the site constantly and supplant Jack's number with his insta-relay, so when you go to call Jack you reach Jack, but Mike is listening to everything you have to say. – Jeff Meden Mar 21 '16 at 16:16
  • @Jeff Meden I have to admit I didn't even think about relays (I'm definitely not a security expert). However, if by "insta-relay" you mean a relay on the telco operator side(from the MSC, I guess), I don't really know how could one detect this attack, let alone prevent it. Do you have any ideas? – A. Darwin Mar 21 '16 at 17:17
  • @A.Darwin I was meaning some tool that simply forwarded the call through: if Mike got ahold of the site info somehow, and found that Jack put in 555-1234, he could quickly replace it with 555-4321 and set up a relay to forward calls to Jack's # (one way to guard is to keep a # history but we are presuming we want everything burned). Then Jason calls and greets Jack, unaware that the whole conversation is recorded. The way to thwart that specifically would be for Jack to post the info encrypted against a pad (that Jason planted on Jack) so that Mike couldn't recreate it at will. – Jeff Meden Mar 21 '16 at 17:56
  • @Jeff Meden You're definitely right. I posted a question on meta to be sure that I can edit my answer to consider an additional case. Once someone confirms, I will edit this answer to include your suggestion (giving you credit, of course). – A. Darwin Mar 21 '16 at 18:20
  • Assuming you can pass a code word to jack and that the phone will be thrown away after, why do you even need a stealthy web site. Why not just a pre-agreed web site's user comment section and any generic (but recognizable to them) message with phone number digits in it? – simpleuser Mar 22 '16 at 19:58
  • @user1663987 if you write the complete phone number in a generic website, chances are that it could be crawled and subject at least to a cursory search by someone( especially if the phone number appears out of context). If, on the other hand, you are suggesting some kind of text-based steganography, you are right. However, given such a dangerous situation, I would like to restrict as far as possible the distribution of the phone numbers. Plus, I think that my scheme would be more scalable. – A. Darwin Mar 22 '16 at 20:32
  • Another (marginal) point: even if the phone number is not crawled by your adversaries, it may be collected by spammers, shady marketing companies, possibly cybercriminals. And I guess that you wouldn't want to be flooded by random/annoying calls and messages in the middle of an op. – A. Darwin Mar 22 '16 at 20:38
  • @A.Darwin But as a burner phone, won't you only be holding on to it for a very short time? And if someone calls without the code word, you hang up (and the garbage calls help hide the real call). – simpleuser Mar 22 '16 at 21:46
  • @user1663987 True, it is used for a short time, but remember that "a lifetime of hours" may well mean 6-8-10 hours. As for the garbage calls hiding the real one, I'm not so sure. Traffic analysis would immediately recognize short, incoming calls and discard them. One could, however, call random public numbers (restaurants,...) in an attempt to hide the real call. – A. Darwin Mar 23 '16 at 06:36
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Burner phones may not typically be used like that, although they could be. To answer your little scenario, you can try area code tricks with hidden messages stored somewhere that's accessible to each of you.

This answer assumes you have to register the phone and provide details. If you don't have to register, this answer does not apply.

Area Code Registration Tricks

This is the first step. It's all in the area code. You both sign up in the same area, using two real addresses in the same zip code, in somewhat close proximity within the same hour.

They are not your addresses, but that doesn't matter. Many places in the U.S. require you to register with an actual address. Both of you will now be given similar phone numbers with the same area code, and the same local code:

  1. Jason Bourne: 707-555-0001

  2. Jack Bauer: 707-555-0100

You and Bauer will be using some kind of protocol, somewhere, somehow, where either of you can find the last four digits of each other's phone number using something that only the two of you know.

Hidden Messages

This is the second step.

  1. Here's a rough example that is easy to understand: Bauer then posts something like ABAA. Your little "cipher" decodes A to 0, and B to 1. When decoded, this translates to 0100. And then you call 1-707-555-0100.

  2. Hiding in plain sight is much better, as there are lots of ways to hide messages in every day sentences that don't stand out, or make people suspicious. Maybe you'll have a programmable answering machine where you can set the recording of a phone number that both of you know.

    *"Hi, mom. I'll be late to Christmas Dinner. My plane was delayed. It's really cold here. Literally 0 degrees. I'll arrive around 1 O'Clock. Save me some meatloaf! MOM! THE MEATLOAF! So cold... can you believe it? It's zero degrees!"

Even if someone decodes your little trick, they find four numbers. What are they going to do with it? There's a lot of different possibilities as to what those numbers mean. Good luck figuring it out. You should use something other than A=0, and B=1. It's just there are a rough example.

Community
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Mark Buffalo
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    This is a third-party trick. Using a code and hidden messages is a degree of indirection, and presumes either a third-party to exchange the information or pre-arranged signal that acts itself like a third party would. – Brent Kirkpatrick Mar 20 '16 at 22:49
  • That "area code registration trick" won't work in many places. For example, I purchased new phones a few years ago in Phoenix, AZ, one was given a 623 area code, and the other was a 480 area code. It would be wiser to simply have a way of communicating the entire number, as purchasing even from different carriers or stores would run the same risk. –  Mar 22 '16 at 18:04
  • @Thebluefish Agreed, but actually, you can usually choose the area code you want to use. And if it's in the same general area, with the same address, you can make it choose something by default. Also, you can know the chosen area codes for a particular city and add a few details. – Mark Buffalo Mar 22 '16 at 18:05
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    The US is one of the few countries that actually uses geographic area codes for mobile phone numbers. Most countries use a fixed range or a few prefixes for mobile numbers. The UK uses 71xx, 072xx, 073xx, 074xx, 075xx, 07624, 077xx, 078xx, and 079xx. Different operators sometimes have different prefixes and in some cases its just random. – papirtiger Mar 22 '16 at 21:27
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Are we talking disposal within minutes/hours of purchasing the phone or is it disposal immediately after making/receiving a single call ("per-action, or per-call basis")? If the latter is the case, then the simple solution is to start off with two phones each and to buy new phones such that you always have two. The first phone number to be used by each will need to be communicated either in person or secretly by one of the methods that's outlined in other answers.

But for the first call, Jason and Jack can verbally tell the other what their next phone number will be and then dispose of the first phone. The next phone remains unused until they make contact with each other again, they give each other the next number for the third phone, and the process keeps repeating.

Dr.DrfbagIII
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1.- Kiosk sellers may be part of the network and the cards that have been given may have been known by both agents previously.

2.- They don't use the phone, they use its ability to connect to the Internet to communicate with that phone. So they call using prestablished Internet acconts that allow voice calls, or they may not need to use the voice at all.

YoMismo
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  • That's it. Meet me in the Darknet only. – ott-- Mar 22 '16 at 22:25
  • I'm not so sure about 1. Jason buys his phone in London, Jack in LA. Of course, it is possible for an international network of kiosk sellers to exist, but it would probably be managed by the CIA/whatever agency you work for. If Jason Bourne is a former CIA agent, hunted by the Agency, it would be wise to not use CIA resources. – A. Darwin Mar 23 '16 at 06:49
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  1. Meet:

    a. each other at the same time

    b. a 3rd party

  2. Securely send a number one-way through a known communication channel by encrypting it with something like a one-time pad

Anything else would be variation of these.

user1886419
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  • why would you need a 3rd party? – A. Darwin Mar 21 '16 at 07:27
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    @A.Darwin: at risk of stating the obvious, in order to not meet each other at the same time. That might either be because it's operationally unsound to meet or just because it's difficult to match schedules. – Steve Jessop Mar 21 '16 at 11:40
  • @SteveJessop Ah I see... I was confused because I thought that they needed to meet each other at the same time and need a 3rd party ,as well. Now it's definitely more clear. – A. Darwin Mar 21 '16 at 12:13
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Get a third party to buy the phone for you, so that you're not caught on camera.

Setup a web site or newsgroup (preferably as a TOR service) and tell Jack the address beforehand. Make sure it's hosted in a non-Fourteen Eyes country.

Get Jack's public key beforehand. Preferably, give him your public key too.

Encrypt [and sign] the message (which has your your phone number) and post it to the web site or newsgroup.

You could post several other fake messages encrypted with other keys to the same site/group. The one Jack can decrypt is the real one.

Neil McGuigan
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Once Jason gets his phone, he sends an email with the number to a public Mailinator inbox:

https://www.mailinator.com/

The inbox name is a shared secret that only Jason and Jack know. Further to this, the number is encrypted using some coding scheme that only Jason and Jack know. Jack picks up the number from there. This is not very secure, but obscure enough that Jason and Jack stay ahead of the game for long enough to make a few calls before discarding their phones/sims for new ones.

user2800708
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PGP over Twitter

Whatever method they chose, they must first make a trusted exchange of information. Either they both trust a leader and set up an symmetric encryption channel through him. Or one of them trusts the other. Or they meet in person.

Before the meeting, each generates a big set of private keys. They might even get away with generating them from a 12 word seed (the bitcoin wallet electrum.org works like this). At the meeting they exchange the public keys.

Now sending PGP messages and hash-tagging them with the public key they encoded with is enough to communicate securely (from an open wifi spot).

The problem is they look awfully suspicious. So they are going to take one more step and agree on some fixed dictionary, preferably with simple english words. Now they are going to encode they're messages with this dictionary. The end result is they communicate through gibberish tweets "correct horse battery staple #foxladder". The gibberish though is simple english so it's going to be a pain to search for.

In this case "fox ladder" is the first part of the public key the message is encoded with. The other person knows his public keys so he can keep searching twitter until a message appears for him.

csiz
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You place a key-pair signed & encrypted message within a steganographically encoded image, and then you place that image in a public forum / social media. Make the image a funny meme or cat picture, so it will be widely disseminated by unwitting helpers. The intended recipients will be able to decrypt the message, and the image will be disseminated widely enough to mask the actual intended recipients.

Byron Jones
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One possible way was demonstrated on an episode of "Person of Interest". The two protagonists' usual communications are blown, but they need to get in touch.

They independently pick up burner phones, then one of them calls a pre-arranged number and leaves a message containing their phone number. The other can call the number and retrieve the message.

It's assumed that the answering service has never been used before, and is, presumably, itself disposable.

I further assume that when leaving the message, the phone number is obscured by some pre-arranged scheme (e.g. adding the digits of the number of their favourite deli to the given number).

I don't think they did it in the show, but you'd presumably call the answering service from payphones, rather than from the burner phone, so that anyone who knows about the answering service and is tracing the call doesn't get the burner phones.

Roger Lipscombe
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There are any number of ways to communicate with someone these days. Forums provide the easiest method. There are tons of them out there, they're easily accessed, and there's so much activity that there's no way to keep track of everything. You would need to agree before hand on which forum to use, and how to encode your message. The choice of forum and username could even be part of the code.

Jonathan
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