Cries of spies as audit group finds possible 'backdoor' in Bittorrent Sync

Hashes gone AWOL: bugged or just buggy?

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Updated: BitTorrent responds Popular file sharing platform BitTorrent Sync is 'probably' leaking hashes to its website and access to shared data, a group audit has found.

The platform downloaded some 10 million times allowed users to synchronise data over networks using encrypted peer-to-peer at speeds said to be 16 times faster than Dropbox, using architectures intentionally designed to be secure.

The research group operating under the popular Hackito conference said security flaws the severity of which was unconfirmed could be the result of a backdoor to facilitate tapping by the National Security Agency and friends.

"[A] change of sharing paradigm that introduced this vulnerability happened after the first [Bittorrent Sync] releases," the group wrote in a report.

"This may be the result of National Security Letters, from [the] US Government to businesses to pressure them in giving out the keys or introducing vulnerabilities to compromise previously secure systems that could have been received by BitTorrent Inc and / or developers."

One BitTorrent Sync staffer 'kos13' moved to quash the security hole was a deliberate backdoor.

"[The] researcher hasn't found anything bad, besides [a] few crashes on random tests.

"There is nothing even close to 'Bittorrent Inc has access to all your encrypted files'."

They said the company was working on a more detailed response.

Seven security issues marked high severity were reported including some in a web admin interface and various leaks.

Five medium vectors were found including dependence on possibly insecure architecture and leaking of IP addressees to trackers.

Readers could follow the technical analysis, or community commentary.

Update BitTorrent comms director Christian Averill told Vulture South the group remains confident of the security of Sync, dubbing the claims "pretty wild" derived from a "pretty loose" methodology.

His response in full:

  • BitTorrent Sync remains the most secure and private way to to move data between two or more devices. And for good reason, we've built it that way. Rigorous third-party security audits have been conducted to verify the product's security architecture.
  • But we take questions about Sync's security very seriously. We've gone through the claims made by Hackito and after reviewing it in full, we do not feel there is any cause for concern.
  • For your reference, we address the main points made in the posts conclusion:
  • Folder hashes are not the folder key (secret) and are used to discover other peers with the same folder. 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.
  • Links make use of standard public key cryptography to enable direct and secure key exchange between peers. The link does not contain any folder encryption keys; it only contains the public keys of the machines involved in the exchange. The link itself cannot be used for decrypting the communication.

    After direct connection is established (user can verify that by comparing certificate fingerprint for both peers) Sync will pass folder key over encrypted channel for other peer. In addition, the public key and the folder hash appear after the # sign in the URL, which means that all modern browsers won't even send this to the server.

    On top of that, a few additional features were implemented to further secure the key exchange using links, including (1) the links automatically expire within three days (set as default) and (2) explicit approval is required by the inviting peer before any key exchange takes place (also set as a default).

  • We host a tracker server for peer discovery; the tracker is only there to enable peers to find each other. It is not a part of the folder exchange. As mentioned earlier, the hashes cannot be used to obtain access to a folder.
  • Like with any other solution, the user needs to secure access to their machines using proper passwords, proper firewall configuration, and the like. Once an attacker has root access or physical access to the machine, it can modify any element of the attacked system. This is not an issue with Sync, but basic security protocol.
  • Sync security is completely dependent on client-side implementation. The public infrastructure is there to enable better connectivity and more user-friendly folder sharing experience. Compromising the public infrastructure cannot impact the security of Sync.

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