CGD(4) | Device Drivers Manual | CGD(4) |
cgd
—
pseudo-device cgd
cgd
driver, configured with the
cgdconfig(8) tool, implements
a logical disk device by encrypting or decrypting disk sectors on their way to
and from a physical backing disk or partition.
cgd
keeps the
content of the disk secret from a passive adversary, such as
a thief who steals your disk or a border patrol agent who detains you and
takes a snapshot of your laptop's disk while you are crossing a border.
cgd
does not detect
tampering by an active adversary who can modify the
content of the backing store, such as a man-in-the-middle between you and an
iSCSI target, or after the border patrol returns your laptop to you.
adiantum
(key size: 256 bits)
Adiantum provides the best security by encrypting entire disk sectors at a time (512 bytes), and generally provides the best performance on machines without CPU support for accelerating AES.
aes-cbc
(key sizes: 128, 192, or 256 bits)
aes-xts
(key sizes: 256 or 512 bits)
WARNING: These obsolete ciphers are implemented without timing side channel protection, so, for example, JavaScript code in a web browser that can measure the timing of disk activity may be able to recover the secret key. These are also based on 64-bit block ciphers and are therefore unsafe for disks much larger than a gigabyte. You should not use these except where compatibility with old disks is necessary.
3des-cbc
(key size: 192 bits)
Note: Internally, the ‘parity bits’ of the 192-bit key are ignored, so there are only 168 bits of key material, and owing to generic attacks on 64-bit block ciphers and to meet-in-the-middle attacks on compositions of ciphers as in EDE3 the security is much lower than one might expect even for a 168-bit key.
blowfish-cbc
(key sizes: 40, 48, 56, 64, ..., 432, 440, or 448 bits)
cgd
had a bug in the CBC-based
ciphers aes-cbc
, 3des-cbc
, and
blowfish-cbc
: the CBC initialization vector was chosen
to be the eight-fold encryption under the block cipher of
the little-endian encoding of the disk sector number, which has no impact on
security but reduces performance. For compatibility with such disks, the
‘IV method’ must be set to encblkno8
.
Otherwise the ‘IV method’ should always be
encblkno1
. The parameter is meaningless for
adiantum
and aes-xts
.
cgd
responds to all of the standard disk
ioctl(2) calls defined in
sd(4), and also defines the
following:
CGDIOCSET
cgd
. This
ioctl(2) sets up the
encryption parameters and points the cgd
at the
underlying disk.CGDIOCCLR
cgd
.CGDIOCGET
cgd
.These ioctl(2)'s and
their associated data structures are defined in
<dev/cgdvar.h>
header.
cgd
, then you have irrevocably lost all of
the data on the disk. Please ensure that you are using an appropriate backup
strategy.
cgd
device special files.Roland C. Dowdeswell and John Ioannidis, The CryptoGraphic Disk Driver, Proceedings of the FREENIX Track: 2003 USENIX Annual Technical Conference, USENIX Association, https://www.usenix.org/event/usenix03/tech/freenix03/full_papers/dowdeswell/dowdeswell.pdf, 179-186, June 9-14, 2003.
Paul Crowley and Eric Biggers, Adiantum: length-preserving encryption for entry-level processors, International Association of Cryptologic Research, Transactions on Symmetric Cryptology, 4, 2018, https://doi.org/10.13154/tosc.v2018.i4.39-61, 39-61.
FIPS PUB 46-3: Data Encryption Standard (DES), National Institute of Standards and Technology, https://csrc.nist.gov/publications/detail/fips/46/3/archive/1999-10-25, United States Department of Commerce, October 25, 1999, withdrawn May 19, 2005.
FIPS PUB 197: Advanced Encryption Standard (AES), National Institute of Standards and Technology, https://csrc.nist.gov/publications/detail/fips/197/final, United States Department of Commerce, November 2001.
Morris Dworkin, Recommendation for Block Cipher Modes of Operation: Methods and Techniques, National Institute of Standards and Technology, https://csrc.nist.gov/publications/detail/sp/800-38a/final, United States Department of Commerce, December 2001, NIST Special Publication 800-38A.
Morris Dworkin, Recommendation for Block Cipher Modes of Operation: the XTS-AES Mode for Confidentiality on Storage Devices, National Institute of Standards and Technology, https://csrc.nist.gov/publications/detail/sp/800-38e/final, United States Department of Commerce, January 2010, NIST Special Publication 800-38E.
Bruce Schneier, The Blowfish Encryption Algorithm, https://www.schneier.com/academic/blowfish, superseded by Twofish, superseded by Threefish.
Karthikeyan Bhargavan and Gaëtan Leurent, Sweet32: Birthday attacks on 64-bit block ciphers in TLS and OpenVPN, https://sweet32.info.
cgd
driver was written by Roland C. Dowdeswell for
NetBSD. The cgd
driver
originally appeared in NetBSD 2.0. The
aes-xts
cipher was added in NetBSD
8.0. The adiantum
cipher was added in
NetBSD 10.0.
August 16, 2020 | NetBSD 10.0 |