On Wed, Sep 11, 2019 at 07:34:31PM +0000, Pascal Van Leeuwen wrote: > > -----Original Message----- > > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > Sent: Wednesday, September 11, 2019 6:06 PM > > To: Pascal van Leeuwen <pascalvanl@xxxxxxxxx> > > Cc: linux-crypto@xxxxxxxxxxxxxxx; antoine.tenart@xxxxxxxxxxx; herbert@xxxxxxxxxxxxxxxxxxx; > > davem@xxxxxxxxxxxxx; Pascal Van Leeuwen <pvanleeuwen@xxxxxxxxxxxxxx> > > Subject: Re: [PATCH 4/7] crypto: testmgr - Added testvectors for the ofb(sm4) & cfb(sm4) > > skciphers > > > > On Wed, Sep 11, 2019 at 12:38:21PM +0200, Pascal van Leeuwen wrote: > > > Added testvectors for the ofb(sm4) and cfb(sm4) skcipher algorithms > > > > > > > What is the use case for these algorithms? Who/what is going to use them? > > > > - Eric > > > SM4 is a Chinese replacement for 128 bit AES, which is mandatory to be used for many > Chinese use cases. So they would use these whereever you would normally use ofb(aes) > or cfb(aes). Frankly, I'm not aware of any practicle use cases for these feedback > modes, but we've been supporting them for decades and apparently the Crypto API > supports them for AES as well. So they must be useful for something ... > > The obvious advantage over CBC mode was that they only require the encrypt part of > the cipher, but that holds for the (newer) CTR mode as well. So, my guess would be > some legacy uses cases from before the time CTR mode and AEAD's became popular. > > Maybe someone remembers why these were added for AES in the first place? > So if you have no idea why they should be added, why are you adding them? - Eric
