dm-crypt

Benchmarking an encrypted dm-crypt/LVM/ext3/SELinux hard drive with bonnie++ and hdparm

I'm going to set up a new laptop system soonish (more on that later) which shall have a completely encrypted hard drive. Hence, I'm testing a few setups wrt security, performance, manageability and fault-tolerance.

Here's a few performance tests I did on an 80 GB laptop hard drive (in an Intel Celeron based laptop, 1.7 GHz, 256 MB RAM, Linux 2.6.17, Debian unstable).
I ran bonnie++ (with no options) and hdparm as hdparm -tT /dev/hda each time. I haven't put too much thought into the test setup, so if I made some stupid mistakes, please let me know.

Unencrypted plain ext3 partitions:

  • Extra partitions for /, /boot, /usr, /var, /tmp, /home, and swap (no LVM).
  • Optionally, SELinux enabled on that system (targeted policy in permissive mode).

bonnie++:

Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
forest         432M 19857  84 21831  10  9536   4 16355  58 22165   3 148.8   0
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16  1650  98 +++++ +++ +++++ +++  1734  98 +++++ +++  3820  96
forest,432M,19857,84,21831,10,9536,4,16355,58,22165,3,148.8,0,16,1650,98,+++++,
+++,+++++,+++,1734,98,+++++,+++,3820,96

bonnie++ with SELinux:

Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
forest         432M 20321  90 21036  13  9473   5 16742  61 21978   4 148.1   0
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16  1398  98 +++++ +++ +++++ +++  1473  98 +++++ +++  3305  98
forest,432M,20321,90,21036,13,9473,5,16742,61,21978,4,148.1,0,16,1398,98,+++++,
+++,+++++,+++,1473,98,+++++,+++,3305,98

hdparm:

 Timing cached reads:   1416 MB in  2.00 seconds = 707.48 MB/sec
 Timing buffered disk reads:   82 MB in  3.06 seconds =  26.80 MB/sec

hdparm with SELinux:

 Timing cached reads:   1404 MB in  2.00 seconds = 700.59 MB/sec
 Timing buffered disk reads:   80 MB in  3.02 seconds =  26.53 MB/sec

Ext3 partitions on top of LVM on top of dm-crypt:

  • One partition which is encrypted using dm-crypt (aes-cbc-essiv:sha256 mode, AES, 256 bit key size)
  • On top of that an LVM2 system, with extra partitions for /, /boot, /usr, /var, /tmp, /home, and swap.
  • Optionally, SELinux enabled on that system (targeted policy in permissive mode).

bonnie++:

Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
forest         464M 11149  54 16660  20  6461   5  7472  58 11129   5 136.4   0
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16  1564  98 +++++ +++ +++++ +++  1650  98 +++++ +++  2640  97
forest,464M,11149,54,16660,20,6461,5,7472,58,11129,5,136.4,0,16,1564,98,+++++,
+++,+++++,+++,1650,98,+++++,+++,2640,97

bonnie++ with SELinux:

Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
forest         464M  9878  52 12138  11  5457   6  6834  56 11037   5 137.2   0
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16  1426  97 +++++ +++ +++++ +++  1451  98 +++++ +++  2433  97
forest,464M,9878,52,12138,11,5457,6,6834,56,11037,5,137.2,0,16,1426,97,+++++,
+++,+++++,+++,1451,98,+++++,+++,2433,97

hdparm:

 Timing cached reads:   1408 MB in  2.00 seconds = 704.01 MB/sec
 Timing buffered disk reads:   80 MB in  3.02 seconds =  26.53 MB/sec

hdparm with SELinux:

 Timing cached reads:   1396 MB in  2.00 seconds = 698.06 MB/sec
 Timing buffered disk reads:   82 MB in  3.07 seconds =  26.69 MB/sec

So yes, there is some overhead, but it's nothing too serious, IMHO. And quite honestly, I don't care too much about performance here — security is more important than performance. I think you'll agree; if you don't agree now, you will agree with me on the very day someone steals your laptop ;-)

HOWTO: Disk encryption with dm-crypt / LUKS and Debian [Update]

A few weeks ago I published a small HOWTO for using loop-aes to encrypt your hard drive, usb thumb drive etc.

As I have bought a new 300 GB external USB disk drive on Friday, I have tried something new this time: disk encryption using dm-crypt / LUKS. It has been suggested to me multiple times that dm-crypt is superior to loop-aes, however I didn't get a real reason. Yes, it doesn't require any kernel patches and is easier to setup. But has any serious cryptographer looked at it sharply, yet? Did it withhold his eye contact?

Anyways, here's how I encrypted my 300 GB drive. I largely followed the guide at the EncryptedDeviceUsingLUKS wiki page...

  1. Make sure you run Linux 2.6.16 or better. Previous versions suffer from an implementation problem which affects the security of dm-crypt, see Linux Kernel dm-crypt Local Cryptographic Key Disclosure.
  2. Enable the following options in your kernel:

    • Code maturity level options
      • Prompt for development and/or incomplete code/drivers
    • Device Drivers -> Multi-device support (RAID and LVM)
      • Device mapper support
      • Crypt target support
    • Cryptographic options
      • AES cipher algorithms
  3. Overwrite the whole drive with random data in order to slow down attacks on the encryption. At the same time perform a bad blocks scan to make sure the hard drive is not going to die too soon:
    badblocks -c 10240 -s -w -t random -v /dev/sdb
    Replace /dev/sdb with whatever is correct on your system. If you're really paranoid, and are willing to wait one or two days, do this:
    dd if=/dev/urandom of=/dev/sdb
  4. Install the required packages:
    apt-get install cryptsetup
    The current cryptsetup in Debian unstable already supports LUKS, which was not the case a while ago, if I'm not mistaken. So Debian testing or stable will most probably not work!
  5. Create one or more partitions on the drive:
    cfdisk /dev/sdb
    I created one big 300 GB partition, /dev/sdb1.
  6. Setup LUKS:
    cryptsetup --verbose --verify-passphrase luksFormat /dev/sdb1
    Enter a good passphrase here. Don't spoil the whole endeavour by chosing a stupid or short passphrase.
  7. Open the encrypted device and assign it to a virtual /dev/mapper/samsung300gb device:
    cryptsetup luksOpen /dev/sdb1 samsung300gb
  8. Create a filesystem on the encrypted device:
    mkfs.ext3 -j -m 1 -O dir_index,filetype,sparse_super /dev/mapper/samsung300gb
    I used ext3 with some optimizations, see mke2fs(8).
  9. Mount the encrypted partition:
    mkdir /mnt/samsung300gb
    mount /dev/mapper/samsung300gb /mnt/samsung300gb
    That's it. Everything you write to /mnt/samsung300gb will be encrypted transparently.
  10. For unmounting use:
    umount /mnt/samsung300gb
    cryptsetup luksClose /dev/mapper/samsung300gb

After unmounting, nobody will be able to see your data without knowing the correct passphrase. Drive is stolen? No problem. Drive is broken, and you want to send it in for repair without the guys there poking in your data? No problem. You leave the USB drive at home and some jerk breaks into your house, steals your drive, rapes your wife, and kills your kids? No problem. Well, sort of, but you get the idea ;-)

There's more things you can do, thanks to LUKS: have multiple passphrases which unlock your data, change/add/remove passphrases as you see fit, etc.

Comments?

Update 2006-04-17: You have to use cryptsetup from unstable if you want LUKS support. cryptsetup in testing does not support this (thanks Ariel).

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