NetBSD/share/man/man4/cgd.4

.\" $NetBSD: cgd.4,v 1.12 2008/09/13 09:13:14 wiz Exp $
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.\" Copyright (c) 2002, 2003 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Roland C. Dowdeswell.
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.Dd September 12, 2008
.Dt CGD 4
.Os
.Sh NAME
.Nm cgd
.Nd cryptographic disk driver
.Sh SYNOPSIS
.Cd "pseudo-device cgd" Op Ar count
.Sh DESCRIPTION
The
.Nm
driver provides the capability of encrypting blocks on their way
to and from a disk or partition.
.Pp
In order to compile support for the
.Nm
into your kernel, you must add the driver to your kernel configuration
file.
To do this, add a line similar to:
.Bd -unfilled -offset indent
pseudo-device   cgd     4       # cryptographic disk driver
.Ed
.Pp
The count argument defines how many
.Nm Ns 's
may be configured at a time.
.Ss Encryption Algorithms
Currently the following cryptographic algorithms are supported:
.Bl -tag -width indentxxxxxxx
.It 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.
.It 3des-cbc
Triple DES in CBC mode.
Triple DES uses a 64 bit blocksize 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.
.It 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.
.El
.Ss IV Methods
Currently, the following IV Methods are supported:
.Bl -tag -width encblkno1
.It 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
.Xr cgdconfig 8
when configuring new
.Nm Ns 's .
.It encblkno8
This is the original IV method used by
.Nm
and provided for backward compatibility.
It repeatedly encrypts the block number 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 unpredictable.
The eightfold encryption was not intended and causes a notable
performance loss with little (if any) increase in security over a
single encryption.
.El
.Ss IOCTLS
A
.Nm
responds to all of the standard disk
.Xr ioctl 2
calls defined in
.Xr sd 4 ,
and also defines the following:
.Bl -tag -width CGDIOCSET
.It CGDIOCSET
configure the
.Nm .
This
.Xr ioctl 2
sets up the encryption parameters and points the
.Nm
at the underlying disk.
.It CGDIOCCLR
unconfigures the
.Nm .
.El
.Pp
These
.Xr ioctl 2 Ns 's
and their associated data structures are defined in
.Pa /usr/include/dev/cgdvar.h .
.Sh WARNINGS
It goes without saying that if you forget the passphrase that you used
to configure a
.Nm ,
then you have irrevocably lost all of the data on the disk.
Please ensure that you are using an appropriate backup strategy.
.Sh FILES
.Bl -tag -width indentxxxxxxxxxxx
.It /dev/{,r}cgd*
.Nm
device special files.
.El
.Sh SEE ALSO
.Xr config 1 ,
.Xr ioctl 2 ,
.Xr sd 4 ,
.Xr MAKEDEV 8 ,
.Xr cgdconfig 8
.Sh HISTORY
The
.Nm
driver was written by Roland C. Dowdeswell for
.Nx .
The
.Nm
driver originally appeared in
.Nx 2.0 .