Security in the WOD's networking layer

When you use the WOD, you are connected to the global network of WOD users. You immediately begin exchanging data packets with all your peers on the network to increase redundancy for your packets and to ensure that your data is stored permanently. In addition, clients may request specific packets at any time - requests that must be replied to if the network is supposed to work properly.

In order to guarantee a certain level of privacy for each WOD user, we use a packet-level encryption scheme. This scheme needs to allow the WOD's similarity-based capabilities to continue working and therefore encrypting a given cleartext packet must produce the same ciphertext for all clients that perform the encryption. This is of critical importance since the benefits gained from the self-similarity of data in the network are lost immediately if there are two possible ciphertext results for the same cleartext.

To circumvent this issue, each packet is encrypted with it's own MD5 hash. This guarantees that every client encrypting a given packet will encrypt it exactly the same way. Pointer blocks/packets maintain both the fingerprint of the packet (the SHA-1 hash of the cleartext) as well as the password of the packet (the MD5 hash of the cleartext). The security of MD5 is not really an issue here since collisions in the hashing function do not significantly reduce the strength of the generated password.

Packets are encrypted using AES - a symmetric encryption algorithm. This is because the key for a given encrypted block is determined by the block's data itself. Generating public/private keypairs might enhance security but would make things a lot more complicated to implement.

This encryption scheme is not proof against chosen plaintext attacks: if an attacker has a file and wants to prove that you have the file too they are able to regardless of the encryption. This does mean however that only people with the same files as you can prove you have those files. Users would be well advised to employ third-party (higher level) encryption for their files if additional security is needed at this level. The rationale for not implementing per-user security is that, for the most part, as long as I own the same file as you, I don't care if you see that I own it.