CGD(4)                  NetBSD Kernel Interfaces Manual                 CGD(4)


NAME
cgd -- cryptographic disk driver
SYNOPSIS
pseudo-device cgd [count]
DESCRIPTION
The cgd driver provides the capability of encrypting blocks on their way to and from a disk or partition. In order to compile support for the cgd into your kernel, you must add the driver to your kernel configuration file. To do this, add a line similar to: pseudo-device cgd 4 # cryptographic disk driver The count argument defines how many cgd's may be configured at a time. Encryption Algorithms Currently the following cryptographic algorithms are supported: aes-cbc AES in CBC mode. AES uses a 128 bit blocksize and can accept keys of length 128, 192, or 256. The default key length is 128. 3des-cbc Triple DES in CBC mode. Triple DES uses a 64 bit block- size and is performed in EDE3 mode with a 168 bit key. The key passed to the kernel is 192 bits but the parity bits are ignored. blowfish-cbc Blowfish in CBC mode. Blowfish uses a 64 bit blocksize and can accept keys between 40 and 448 bits in multiples of 8. It is strongly encouraged that keys be at least 128 bits long. There are no performance advantages of using shorter keys. The default key length is 128 bits. IV Methods Currently, the following IV Methods are supported: encblkno1 This method encrypts the block number of the physical disk block once with the cipher and key provided and uses the result as the IV for CBC mode. This method should ensure that each block has a different IV and that the IV is reasonably unpredictable. This is the default method used by cgdconfig(8) when configuring new cgd's. encblkno8 This is the original IV method used by cgd and provided for backward compatibility. It repeatedly encrypts the block num- ber of the physical disk block eight times and uses the result as the IV for CBC mode. This method should ensure that each block has a different IV and that the IV is reasonably unpre- dictable. The eightfold encryption was not intended and causes a notable performance loss with little (if any) increase in security over a single encryption. IOCTLS A cgd responds to all of the standard disk ioctl(2) calls defined in sd(4), and also defines the following: CGDIOCSET configure the cgd. This ioctl(2) sets up the encryption parameters and points the cgd at the underlying disk. CGDIOCCLR unconfigures the cgd. These ioctl(2)'s and their associated data structures are defined in /usr/include/dev/cgdvar.h.
WARNINGS
It goes without saying that if you forget the passphrase that you used to configure a cgd, then you have irrevocably lost all of the data on the disk. Please ensure that you are using an appropriate backup strategy.
FILES
/dev/{,r}cgd* cgd device special files.
SEE ALSO
config(1), ioctl(2), sd(4), MAKEDEV(8), cgdconfig(8)
HISTORY
The cgd driver was written by Roland C. Dowdeswell for NetBSD. The cgd driver originally appeared in NetBSD 2.0. NetBSD 5.0_RC4 September 12, 2008 NetBSD 5.0_RC4

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