On Fri, 7 Jun 2019 at 19:59, Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > On Fri, Jun 07, 2019 at 04:49:41PM +0200, Ard Biesheuvel wrote: > > One of the issues that I would like to see addressed in the crypto API > > is they way the cipher abstraction is used. In general, a cipher should > > never be used directly, and so it would be much better to clean up the > > existing uses of ciphers outside of the crypto subsystem itself, so that > > we can make the cipher abstraction part of the internal API, only to > > be used by templates or crypto drivers that require them as a callback. > > > > As a first step, this series moves all users of the 'arc4' cipher to > > the ecb(arc4) skcipher, which happens to be implemented by the same > > driver, and is already a stream cipher, given that ARC4_BLOCK_SIZE > > actually evaluates to 1. > > > > Next step would be to switch the users of the 'des' and 'aes' ciphers > > to other interfaces that are more appropriate, either ecb(...) or a > > library interface, which may be more appropriate in some cases. In any > > case, the end result should be that ciphers are no longer used outside > > of crypto/ and drivers/crypto/ > > > > This series is presented as an RFC, since I am mostly interested in > > discussing the above, but I prefer to do so in the context of actual > > patches rather than an abstract discussion. > > > > Ard Biesheuvel (3): > > net/mac80211: switch to skcipher interface for arc4 > > lib80211/tkip: switch to skcipher interface for arc4 > > lib80211/wep: switch to skcipher interface for arc4 > > > > The way the crypto API exposes ARC4 is definitely broken. It treats it as a > block cipher (with a block size of 1 byte...), when it's actually a stream > cipher. Also, it violates the API by modifying the key during each encryption. > > Since ARC4 is fast in software and is "legacy" crypto that people shouldn't be > using, and the users call it on virtual addresses, perhaps we should instead > remove it from the crypto API and provide a library function arc4_crypt()? We'd > lose support for ARC4 in three hardware drivers, but are there real users who > really are using ARC4 and need those to get acceptable performance? Note that > they aren't being used in the cases where the 'cipher' API is currently being > used, so it would only be the current 'skcipher' users that might matter. > In fact, this is what I started out doing, i.e., factor out the core arc4 code into crypto/arc4_lib.c, and make the existing driver a thin wrapper around it, so that we can invoke the library directly. > Someone could theoretically be using "ecb(arc4)" via AF_ALG or dm-crypt, but it > seems unlikely... > Yes, that seems highly unlikely. > As for removing the "cipher" API entirely, we'd have to consider how to convert > all the current users, not just ARC4, so that would be a somewhat different > discussion. How do you propose to handle dm-crypt and fscrypt which use the > cipher API to do ESSIV? > Without having looked in too much detail, ESSIV seems like something that could be moved into the crypto subsystem, and be implemented as a template.
