On Tue, May 08, 2001 at 01:10:03AM -0500, Scott Gregory Miller wrote: > > > > Ok, instead of starting off the Document-header with the crypto key itself, > > let's start it with the SHA1 hash of the crypto key, so Document-header > > looks like: > > > > <2 bytes, byte length of crypto key hash, i.e. 0x0014> > Just use one byte, a hash has no real business producing more than 2048 > bits of output.
Remember, this is part of a general sequence of byte fields with 2-byte length markers. I mean, we could use a 1 byte length for the crypto key hash, and use MPIs for the data length and metadata length, but I think the most important thing is to preserve the generality of being able to parse out a series of byte fields without understanding what they contain -- for the sake of code modularity and extensibility. > > <20 bytes crypto key hash> > > <2 bytes, byte length of data length field> > > <big endian data length> > > <2 bytes, byte length of metadata length field> > > <big endian metadata length> > > > > Now if my limited understanding of crypto is correct, arranging it so > > the plaintext to be encrypted begins with the hash of the crypto key > > is just as good as initializing the IV with some hash function of > > the crypto key, so we can leave the IV initialized to all zeroes, > > right? > Yes, that should be safe, that would give the IV 120 bits of randomness. Great, so I think we almost have a standard for the Document-header now. The only thing I'm still concerned about is padding it out to a power of 2 length. Currently we've agreed to zero-pad, but I don't really see how it's less risky here than in the actual file data. So I propose we: 1. require 2 bytes of zeroes after the last byte field, to give a "null length marker" indicating the end. 2. pad the resulting byte stream using the same technique I proposed for the file data. #1 would also let us drop the requirement that the byte fields not have odd lengths, which was no more than a parser convenience. -- # tavin cole # # "The process of scientific discovery is, in effect, # a continual flight from wonder." # - Albert Einstein _______________________________________________ Devl mailing list Devl at freenetproject.org http://lists.freenetproject.org/mailman/listinfo/devl
