On 20/06/2019 00:37, Eric Biggers wrote: > On Wed, Jun 19, 2019 at 06:29:21PM +0200, Ard Biesheuvel wrote: >> Add an accelerated version of the 'essiv(cbc(aes),aes,sha256)' >> skcipher, which is used by fscrypt, and in some cases, by dm-crypt. >> This avoids a separate call into the AES cipher for every invocation. >> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > > I'm not sure we should bother with this, since fscrypt normally uses AES-256-XTS > for contents encryption. AES-128-CBC-ESSIV support was only added because > people wanted something that is fast on low-powered embedded devices with crypto > accelerators such as CAAM or CESA that don't support XTS. > > In the case of Android, the CDD doesn't even allow AES-128-CBC-ESSIV with > file-based encryption (fscrypt). It's still the default for "full disk > encryption" (which uses dm-crypt), but that's being deprecated. > > So maybe dm-crypt users will want this, but I don't think it's very useful for > fscrypt. The aes-cbc-essiv:sha256 is still default for plain cryptsetup devices (LUKS uses XTS for several years as a default already). The reason is compatibility with older distros (if there is no cipher mode specification in crypttab for plain device, switching default could cause data corruption). But I think initscripts now enforce cipher and keysize crypttab options for some time, so I can probably switch the default to XTS for plain devices soon. (We have already compile time option for it anyway.) IOW intention for dm-crypt is to slightly deprecate CBC mode use for all types of devices. Milan
