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Bittorrent Sync: Security Is Our Highest Priority

80 points by mseri 12y ago

RRRA 12y ago
Still closed source...
jrochkind1 12y ago
> it is a 160 bit number, which means that it is cryptographically impossible to guess the hash of a specific folder. Perhaps they know what they're talking about and are just trying to simplify for a non-technical audience... but that kind of language does not inspire confidence from a technical audience.
- tptacek 12y ago
  ... because...
  - SCHiM 12y ago
    Because saying it like sounds like they are merely using buzzords instead of clearly stating why their system is secure. To me it seemed that the intended result for the user was to think: "super cryptographically secure 160bit secret folders!" While they should have gone for: Our algorithm to hash folders produces hashes 160bits long. Which means that 2^160 -1 different folders can be securely hashed! Of course they diden't say what they meant with 'secure' either. Will two folders that are both very big, and only differ with 1 bit produce the same hash yes or no? Is it possible to reverse this hash easily? Can it be brute forced? That kind of stuff... Having said that, it does appear that this post was aimed at non-technical users. So perhaps it's not a bad way to rebut the claims about leaky security.
    - deleted 12y ago
      [deleted]
    - tedunangst 12y ago
      > Our algorithm to hash folders produces hashes 160bits long. Which means that 2^160 -1 different folders can be securely hashed! Except that's even more wrong. Collisions are expected long before 2^160 - 1 hashes.
      - rich90usa 12y ago
        Quoting Kos's reply: > The hashes cannot be used to obtain access to the folder; it is just a way to discover the IP addresses of devices with the same folder. It would seem that consideration was put in to defending against collision attacks.
    - Cogito 12y ago
      It reads like they said what they meant. The hashes cannot be used to obtain access to the folder; it is just a way to discover the IP addresses of devices with the same folder. Hashes also cannot be guessed; it is a 160 bit number, which means that it is cryptographically impossible to guess the hash of a specific folder. That is, you can only know the hash of a specific folder if a. You have that folder b. Someone told you the hash This follows from using any reasonable hashing algorithm, such as sha-1. Furthermore, because the range of the hash is sufficiently large the chance that you can, guessing randomly, find a valid folder is quite small. There are 2^160 ~= 1.46 x 10^48 possible hashes. Given that the probability of guessing a random folder is (number of folders hashed) / (number of possible hashes), and assuming that there are less than 10^8 folders that have been hashed, the chance of randomly finding any folder is less than 1 in 10^40.
- daeken 12y ago
  I think the use of "cryptographically" there is a bit silly, but otherwise they're spot on. You could have a billion computers, each trying a billion unique guesses per second, for a billion years, and you would've only guessed 0.000000000002158% of the possible values. 160 bits is a lot of bits.
  - pbsd 12y ago
    Well, it would depend on the entropy of the folder. Maybe we know the general structure of the folder, except some crucial short piece of information. Otherwise, everyone would also be fine using SHA-1 to store passwords. N.B: I don't know anything about the protocol, or whether the above applies. But appealing to the strength of a hash function only makes sense for hard-to-guess hashing material, which is not always the case.
  - e12e 12y ago
    Right. But as I read it, the 160bit hash is over the content, in order to find peers with the same content. So if I wonder who's got a certain leaked document, or a certain media file, the hash can be used to xheck for that? Could be enoygh to get a warrant, for example? If I know a certain document, say payslip.pdf and guess it is in a folder named payslips - maybe I could guess the other values and verify my guess with the hash (yeah, probably not a very interesting example ...)
eps 12y ago
While it's a pure implementation issue, it's odd that they haven't at all addressed app's crashing through packet fuzzing, because that's an excellent zero-day candidate.
ef4 12y ago
I'll believe you when you open source it. I've been using syncthing and it's pretty great.
toggle 12y ago
> BitTorrent Sync remains the most secure and private way to to move data between two or more devices. That very first sentence will always be false as long as it isn't open source. (Even the protocol isn't publicly documented, last I checked.) I'm not an open-source purist, but the way they always promote as being the most secure, private option out there while completely ignoring that fact is frustrating. I haven't tried using it, but Pulse[0] appears to be an open source replacement for BitTorrent Sync. I figure it's relevant to this thread. [0]: https://ind.ie/pulse/ https://ind.ie/pulse/ EDIT: ef4 mentioned Syncthing in his comment. Pulse was forked from Syncthing. I think they're still compatible with each other at the moment. Nice explanation at https://discourse.syncthing.net/t/syncthing-is-still-syncthing/1372 https://discourse.syncthing.net/t/syncthing-is-still-syncthi....
- trickz 12y ago
  How would open sourcing it make it more secure? I mean, I understand that doing so would let you look at the code, and maybe even have others find and plug security holes, but your statement seems to imply that closed source is less secure by default, unless I'm missing something.
  - mkonecny 12y ago
    Doesn't necessarily make it more secure, but will increase the confidence that it is the most secure through peer review. Any company will say their products are secure/the best etc. - proof is what makes those claims legit.
    - trickz 12y ago
      Yep, that's fair.
      - jmathai 12y ago
        Completely agree that open source is critical to making claims about security. Else you're asking people to trust you. Not to be pedantic but the gotcha is that you can't know they're using the open source software as-is. If they run a hosted service or distribute binaries you won't know. Also with cryptography any change (diverging from the open source software) can have regressions.
jaseemabid 12y ago
The last time I installed bittorrent on my mac, it came with a chrome extension malware. I used to really love BTSync, but now I'm certainly going to ditch it. For once again proving the point that unless its free software, its not worth it.

80 points by mseri 12y ago

RRRA 12y ago

Still closed source...

> it is a 160 bit number, which means that it is cryptographically impossible to guess the hash of a specific folder. Perhaps they know what they're talking about and are just trying to simplify for a non-technical audience... but that kind of language does not inspire confidence from a technical audience.

tptacek 12y ago
... because...
- SCHiM 12y ago
  Because saying it like sounds like they are merely using buzzords instead of clearly stating why their system is secure. To me it seemed that the intended result for the user was to think: "super cryptographically secure 160bit secret folders!" While they should have gone for: Our algorithm to hash folders produces hashes 160bits long. Which means that 2^160 -1 different folders can be securely hashed! Of course they diden't say what they meant with 'secure' either. Will two folders that are both very big, and only differ with 1 bit produce the same hash yes or no? Is it possible to reverse this hash easily? Can it be brute forced? That kind of stuff... Having said that, it does appear that this post was aimed at non-technical users. So perhaps it's not a bad way to rebut the claims about leaky security.
  - deleted 12y ago
    [deleted]
  - tedunangst 12y ago
    > Our algorithm to hash folders produces hashes 160bits long. Which means that 2^160 -1 different folders can be securely hashed! Except that's even more wrong. Collisions are expected long before 2^160 - 1 hashes.
    - rich90usa 12y ago
      Quoting Kos's reply: > The hashes cannot be used to obtain access to the folder; it is just a way to discover the IP addresses of devices with the same folder. It would seem that consideration was put in to defending against collision attacks.
  - Cogito 12y ago
    It reads like they said what they meant. The hashes cannot be used to obtain access to the folder; it is just a way to discover the IP addresses of devices with the same folder. Hashes also cannot be guessed; it is a 160 bit number, which means that it is cryptographically impossible to guess the hash of a specific folder. That is, you can only know the hash of a specific folder if a. You have that folder b. Someone told you the hash This follows from using any reasonable hashing algorithm, such as sha-1. Furthermore, because the range of the hash is sufficiently large the chance that you can, guessing randomly, find a valid folder is quite small. There are 2^160 ~= 1.46 x 10^48 possible hashes. Given that the probability of guessing a random folder is (number of folders hashed) / (number of possible hashes), and assuming that there are less than 10^8 folders that have been hashed, the chance of randomly finding any folder is less than 1 in 10^40.
daeken 12y ago
I think the use of "cryptographically" there is a bit silly, but otherwise they're spot on. You could have a billion computers, each trying a billion unique guesses per second, for a billion years, and you would've only guessed 0.000000000002158% of the possible values. 160 bits is a lot of bits.
- pbsd 12y ago
  Well, it would depend on the entropy of the folder. Maybe we know the general structure of the folder, except some crucial short piece of information. Otherwise, everyone would also be fine using SHA-1 to store passwords. N.B: I don't know anything about the protocol, or whether the above applies. But appealing to the strength of a hash function only makes sense for hard-to-guess hashing material, which is not always the case.
- e12e 12y ago
  Right. But as I read it, the 160bit hash is over the content, in order to find peers with the same content. So if I wonder who's got a certain leaked document, or a certain media file, the hash can be used to xheck for that? Could be enoygh to get a warrant, for example? If I know a certain document, say payslip.pdf and guess it is in a folder named payslips - maybe I could guess the other values and verify my guess with the hash (yeah, probably not a very interesting example ...)

eps 12y ago

While it's a pure implementation issue, it's odd that they haven't at all addressed app's crashing through packet fuzzing, because that's an excellent zero-day candidate.

ef4 12y ago

I'll believe you when you open source it. I've been using syncthing and it's pretty great.

toggle 12y ago

> BitTorrent Sync remains the most secure and private way to to move data between two or more devices. That very first sentence will always be false as long as it isn't open source. (Even the protocol isn't publicly documented, last I checked.) I'm not an open-source purist, but the way they always promote as being the most secure, private option out there while completely ignoring that fact is frustrating. I haven't tried using it, but Pulse[0] appears to be an open source replacement for BitTorrent Sync. I figure it's relevant to this thread. [0]: https://ind.ie/pulse/ https://ind.ie/pulse/ EDIT: ef4 mentioned Syncthing in his comment. Pulse was forked from Syncthing. I think they're still compatible with each other at the moment. Nice explanation at https://discourse.syncthing.net/t/syncthing-is-still-syncthing/1372 https://discourse.syncthing.net/t/syncthing-is-still-syncthi....

trickz 12y ago
How would open sourcing it make it more secure? I mean, I understand that doing so would let you look at the code, and maybe even have others find and plug security holes, but your statement seems to imply that closed source is less secure by default, unless I'm missing something.
- mkonecny 12y ago
  Doesn't necessarily make it more secure, but will increase the confidence that it is the most secure through peer review. Any company will say their products are secure/the best etc. - proof is what makes those claims legit.
  - trickz 12y ago
    Yep, that's fair.
    - jmathai 12y ago
      Completely agree that open source is critical to making claims about security. Else you're asking people to trust you. Not to be pedantic but the gotcha is that you can't know they're using the open source software as-is. If they run a hosted service or distribute binaries you won't know. Also with cryptography any change (diverging from the open source software) can have regressions.

jaseemabid 12y ago

The last time I installed bittorrent on my mac, it came with a chrome extension malware. I used to really love BTSync, but now I'm certainly going to ditch it. For once again proving the point that unless its free software, its not worth it.