On Tue, Jul 11, 2017 at 10:52 AM, Kamil Konieczny <k.koniec...@partner.samsung.com> wrote: > > Hi, > > I am writing crypto driver for hash MD5/SHA1/SHA256 on Exynos 4412, > and I am facing some (minor?) difficulties. > > In old days, hadware (HW) can only do basic hash block operation, > so at the end it needed to finalize hash, and driver need to > write some bits into buffer to get message hash. Time passes, > and hardware (HW) was designed with improved cappabilities, > so it can add itself bits after message and calculate hash, > it can stop then export state, import and resume, > but ... it can not process null-length (or zero-length) ending. > So there is no more final method. > > It must be feeded with at least one message byte to produce hash. > > One more constrain is to process data in constant-sized chunks, > here it is 64 bytes, the same as for AES block, > i.e. it cannot stop and export state while in middle of block, > example - if we feed 16 bytes, we must then feed 48 bytes > to stop, but ideally we should feed it always 64 bytes.
> > Some crypto drivers with similar problem(s): > > omap-sham.c - no final and blocksize needed, > broadcom bcm/spu.c - no final, > ccp/ccp-crypto-sha.c - no final, > nx/nx-sha256.c - blocksize needed, > > One more thing - in algorithm description for methods: > final, finup, update, digest, export, import > there is note that finup is for those hardware > that cannot do final, but again, > > it looks like crypto framework is ignoring that and every finup > is translated into "update, final". > > HW driver will do opposite - it will translate final into finup. > > From this follows that for every such HW crypto drivers authors > duplicate code for keeping at least blocksize cache of message. > > One more point - use of block size in algo structure. > It is for informing framework about HW limitation, > but seems to be ignored again... > > Any suggestions ? > > Can i keep some bytes unfeeded from ahash_request > and return -EINPROGRESS ? > Should i set timer and copy rest bytes after some timeout, > where no more requests are incoming ? Or not ? cause it is > async mode ? > can i wait for more requests for processing waiting one ? > Your two constraints are actually inter-related - If you can only feed the HW a constant size chunk, than indeed need to keey bytes fed to the driver the are below the chunk size in a software buffer, but than you need the final() method to feed these bytes (padded as needed) to the HW if they are the last bytes Gilad -- Gilad Ben-Yossef Chief Coffee Drinker "If you take a class in large-scale robotics, can you end up in a situation where the homework eats your dog?" -- Jean-Baptiste Queru
