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Wed, 02 Jul 2008

POHMELFS crypto: feel incredibly stupid.

First, POHMELFS does need to have encryption. Because I plan to use distributed hash table approach in server (well, consider POHMELFS kernel client as a kind of bittorrent filesystem client), and as in any non-centralized system, content transferred via uncontrolled data channels has to be encrypted.

But... I'm incredibly stupid: I implemented encryption and decryption in place, i.e. VFS page is being encrypted prior to be written to the servers, so subsequent reading leads to... Yes, it reads encrypted content.
To fix this issue I plan to encrypt data into different pages and send them, leaving VFS ones as is. There are two approaches I consider:

• allocate and send pages at writeback time - we want to send 5 pages, so allocate 5 pages, encrypt data into them and broadcast them to all needed servers.
• allocate (potentially large) pool of pages at mount time per crypto thread and encrypt data into them. This will have about zero run-time overhead for VFS, except slightly delayed because of encryption write completion.

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