Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > > > I wonder if it would help if the input buffer and output buffer didn't > > > > have to correspond exactly in usage - ie. the output buffer could be > > > > used at a slower rate than the input to allow for buffering inside the > > > > crypto algorithm. > > > > > > I don't follow - how could one be used at a slower rate? > > > > I mean that the crypto algorithm might need to buffer the last part of the > > input until it has a block's worth before it can write to the output. > > This is what is typically handled transparently by the driver. When > you populate a scatterlist, it doesn't matter how misaligned the > individual elements are, the scatterlist walker will always present > the data in chunks that the crypto algorithm can manage. This is why > using a single scatterlist for the entire input is preferable in > general. Yep - but the assumption currently on the part of the callers is that they provide the input buffer and corresponding output buffer - and that the algorithm will transfer data from one to the other, such that the same amount of input and output bufferage will be used. However, if we start pushing data in progressively, this would no longer hold true unless we also require the caller to only present in block-size chunks. For example, if I gave the encryption function 120 bytes of data and a 120 byte output buffer, but the algorithm has a 16-byte blocksize, it will, presumably, consume 120 bytes of input, but it can only write 112 bytes of output at this time. So the current interface would need to evolve to indicate separately how much input has been consumed and how much output has been produced - in which case it can't be handled transparently. For krb5, it's actually worse than that, since we want to be able to insert/remove a header and a trailer (and might need to go back and update the header after) - but I think in the krb5 case, we need to treat the header and trailer specially and update them after the fact in the wrapping case (unwrapping is not a problem, since we can just cache the header). David
