[dm-crypt] hardware encryption

Yves-Alexis Perez corsac at debian.org
Thu Mar 14 21:50:23 CET 2013

On jeu., 2013-03-14 at 14:14 +0100, Matthias Schniedermeyer wrote:
> Given that openssl doesn't support AES-NI i'm not surprized.

Where did you get that impression?
> Last time i looked AES-NI support in openssl was "in Limbo" and it
> may 
> still take quite some time(years) until there is a release which 
> officially supports AES-NI. This is despite first patches beeing made 
> available before there was silicon, so openssl is quite a few years 
> behind.

Actually, OpenSSL supports AES-NI since 1.0.1 (see
> I'm using an unofficial "something" (Can't remember what it is excatly
> ) 
> so that openssl can utelize AES-NI which in turn enables AES-NI usage 
> for SSH, so i can use it for scp or rsync over SSH.
> The difference is quite noticable, altough in LANs i just use
> No patching necesarry to saturate Gigabit. :-)
> When i tested it some time back over loopback both AES-128-CBC(*)
> (with 
> AES-NI) and ARCFOUR peaked at about 400MB/s(IIRC), so no problem
> doing 
> the 110MB/s needed to saturate Gigabit.

It all really depends on block size. But on my (Core i7 L640) laptop,
there's really no reason to use rc4 anymore. CBC is not the best
example, aes-128-cbc is indeed accelerated by AES-NI instructions but
you really go fast with a mode using PCLMULQDQD like XTS:

type             16 bytes     64 bytes    256 bytes   1024 bytes   8192
rc4             255340.98k   469098.47k   599298.65k   658621.73k
aes-128 cbc      85363.96k    91553.34k    93105.32k    93570.31k
aes-128-xts     272573.48k   849359.06k  1540640.28k  1956586.50k

It's even stronger when you use authenticated ciphers like GCM if you
compare it against enc+mac. You can't openssl speed on those but using
1k blocs:

for cipher in aes-128-cbc-hmac-sha1 aes-128-gcm rc4-hmac-md5; do echo
$cipher; dd if=/dev/zero bs=1k count=1M | openssl enc -${cipher} -pass
pass:foo > /dev/null; done 
1048576+0 records in
1048576+0 records out
1073741824 bytes (1,1 GB) copied, 3,27757 s, 328 MB/s
1048576+0 records in
1048576+0 records out
1073741824 bytes (1,1 GB) copied, 1,90992 s, 562 MB/s
1048576+0 records in
1048576+0 records out
1073741824 bytes (1,1 GB) copied, 3,40679 s, 315 MB/s

It's a bit out of scope for this list, but that means using dm-crypt
aes-xts-plain64 on an AES-NI CPU really makes sense. On those boxes it
might be even faster to use aes-256-xts than aes-128-cbc.

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