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Bittorrent just announced Bittorrent Sync, which as I understand it is a pure P2P sync solution without a central server that stores your data: Instead, all nodes in the network replicate amongst themselves.

The downside is that it only works if two nodes that need to exchange files are online at the same time. You can get working by having a dedicated server on your network that is always on. However, if you place that in the cloud, you risk others getting to your data.

Is there a way to place a node in a mode where it can replicate all the encrypted data (so that other nodes can always pull the latest data from it), but does not have the ability to decrypt it itself (so that if someone steals the node, your data is not compromised)?

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Did you consider disk encryption on the middleman node? – Satoh Apr 24 '13 at 3:43
That would protected the data when the server is shut down, but not when it is active (which it is supposed to be all the time), because then the disk would be mounted. – Thilo Apr 24 '13 at 4:00
I'd like a clarification on "if you place that in the cloud, you risk others getting to your data.". Is it by breach of server? Because they can only get the data via bittorrent sync if they know the secret. – ptman Apr 24 '13 at 8:02
Please note that the data itself is not encrypted, only the connection, which is based on the "secret". Bit-torrent's main purpose is speed and efficiency, not security. So if disk encryption is not enough for you, your server cannot send you data without having the unencrypted files on it. At least with bit-torrent sync. – Satoh Apr 24 '13 at 14:36
The sync spec mentions "relay servers" that facilitate connections between nodes that are firewalled. Those can work without knowing the secret. I guess what I am looking at is a "proxying relay server" that can push data between nodes even when they are not online at the same time. – Thilo Apr 25 '13 at 3:29

Yes that is possible and thoroughly explained at

In a nutshell: you only give the encrypted node an encrypted (read only)-key which allows taking part in the torrent-swarm without decrypting the files on it and all trusted nodes a key which enables decryption and/or write access.

So, on your local computer:

Do the normal "Add a Sync Folder", click "Generate", but change the first letter of the "Folder sercet" from "A" to "D" (see 1 >and 2), set the "Folder to sync", click "OK", right click on that folder from the list, click "Show Folder Preferences", copy the "Read only secret" (see 3), paste it into Notepad(or other text editor), "Encrypted Read-Only Secret" is the first 33 char of that string with the first letter >changed from a "E" to "F" (see 3 and 4)

real example this time.





At least the current linux GUI client actually directly offers 4)

Now you can paste 4) into the encrypted node and either 2) (RW access) or 3) (RO access) to other unencrypted nodes

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What about storing an iso image on the cloud/vps? you could use some sort of live cd and only set it up when you need it.

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