On Tue, 19 May 2020 at 19:35, Stephan Mueller <smueller@xxxxxxxxxx> wrote: > > Am Dienstag, 19. Mai 2020, 18:21:01 CEST schrieb Ard Biesheuvel: > > Hi Ard, > > > > > To be honest, this looks like the API is being used incorrectly. Is > > this a similar issue to the one Herbert spotted recently with the CTR > > code? > > > > When you say 'leaving the TFM untouched' do you mean the skcipher > > request? The TFM should not retain any per-request state in the first > > place. > > > > The skcipher request struct is not meant to retain any state either - > > the API simply does not support incremental encryption if the input is > > not a multiple of the chunksize. > > > > Could you give some sample code on how you are using the API in this case? > > What I am doing technically is to allocate a new tfm and request at the > beginning and then reuse the TFM and request. In that sense, I think I violate > that constraint. > > But in order to implement such repetition, I can surely clear / allocate a new > TFM. But in order to get that right, I need the resulting IV after the cipher > operation. > > This IV that I get after the cipher operation completes is different between C > and CE. > So is the expected output IV simply the last block of ciphertext that was generated (as usual), but located before the truncated block in the output?
