The irony is that XTS uses two different keys for different parts of the
operation. This means that AES-XTS-256 is AES128 and AES-XTS-512 is
AES256 (security is not increased by the second key).
So, you compared AES with 128 bit encryption with XChaCha with 256 bit.
And despite the doubled key length, XChaCha is still 3 times faster I
would be curious to see how it is about XChaCha 256b against AES 256b
(which is 512 in XTS) on your machine?
If you reduce an algorithm's security to its security margin, XChaCha12
(=12 rounds of XChaCha) has still a higher security margin than AES256
(= AES-XTS-512), and XChaCha12 is obviously even faster than XChaCha20
(20 rounds of XChaCha). So on hardware without AES-NI, the performance
can be heavily increased. Google made a good job with Adiantum imho, and
of course djb with ChaCha
The issue is already at Blivet:
https://bugzilla.redhat.com/show_bug.cgi?id=2077532
Regards,
Chris
On 08/06/2022 04:18, Casper wrote:
I was curious to see if changes were significant on my old Asus laptop:
```
blackbird:~ # cryptsetup benchmark -c xchacha20,aes-adiantum
# Tests approximatifs en utilisant uniquement la mémoire (pas de stockage E/S).
# Algorithme | Clé | Chiffrement | Déchiffrement
xchacha20,aes-adiantum 256b 327,8 MiB/s 345,0 MiB/s
blackbird:~ # cryptsetup benchmark -c aes-xts-plain64
# Tests approximatifs en utilisant uniquement la mémoire (pas de stockage E/S).
# Algorithme | Clé | Chiffrement | Déchiffrement
aes-xts 256b 105,0 MiB/s 103,9 MiB/s
```
Results on a SATA disk (no SSD), and no AES flag in cpuinfo.
Regards,
Casper
py0xc3 a écrit :
Good everning,
I just experienced that, when setting up a new Fedora, Anaconda (both
"Custom" and "Advanced Custom (Blivet-GUI)") always uses aes-xts-plain64 for
disk encryption, even if the hardware does not support AES-NI.
Does it make sense to use xchacha12,aes-adiantum-plain64 by default if there
is no AES-NI in the hardware?
For a general use case, the security advantages of Adiantum can be
neglected; both aes-xts & chacha-adiantum are secure.
But there are big performance disadvantages of AES when there is no AES-NI
(this was the major reason for merging Adiantum into the kernel).
Besides the use of system resources, netbooks and such may have strongly
decreased battery life times with aes-xts (the issue is primarily aes, not
xts).
I tested with Fedora 35, KDE spin; but as the issue is Anaconda-centric, I
expect that other Workstation installations tend to the same behavior.
Adjustments would be limited to Anaconda.
Regards & stay safe,
Chris
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