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Sat, 28 Jun 2008

Need to rethink POHMELFS crypto a bit.

1. Because of encryption problem - data to be encrypted has to be blocksize aligned, so some informaion about padding has to be added into network command as long as crypto data size.

2. IV generation. I decided to extend network command and put there 64 bit IV for given packet. using simple sequence number is enough to protect against repeat message attack.

3. Encryption/hashing data. I decided not to ecnrypt/hash network headers, and only do it for transmitted data. If transaction contains several commands, data for all commands will be encrypted/hashed, in case of hash, signle digest/hmac will be generated and placed into transaction header.

4. It is possible, that I will add strong header checksum, which will be generated only for header and placed into special field. It will be calculated assuming checksum field is zero. This step is optional so far, but network header has 32 reserved bits, which can be used for it.

Right now hashing and encryption work, but are not checked on server (although generated), because of crypto alignment ugliness I decided to rethink approach a bit.
Evolution process in action...

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