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.IX Title "nbdkit-xor-filter 1"
.TH nbdkit-xor-filter 1 2026-10-17 nbdkit-1.49.4 NBDKIT
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH NAME
nbdkit\-xor\-filter \- obfuscate contents of a plugin with XOR
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit \-\-filter=xor [PLUGIN ARGS ...] xor=VALUE xorlen=LENBYTES
\&
\& nbdkit \-\-filter=xor [PLUGIN ARGS ...] xor=rand[:SEED]
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-xor\-filter\*(C'\fR is a filter for \fBnbdkit\fR\|(1) which XORs
(exclusive or) a value across all of the data in the underlying
plugin.  This can be used to obfuscate the contents of a plugin or as
a trivial, insecure, but fast type of encryption.  For proper
encryption, see \fBnbdkit\-luks\-filter\fR\|(1).
.PP
This filter has two modes.  You can XOR with a fixed repeating
pattern:
.PP
.Vb 1
\& nbdkit file disk.img \-\-filter=xor xor=0xDEADBEEF xorlen=4
.Ve
.PP
Or you can XOR with the output of a pseudo\-random number generator
(PRNG) with an optional seed by using \f(CW\*(C`xor=rand[:SEED]\*(C'\fR.  The result
is more obfuscated.  In this mode \f(CW\*(C`xorlen\*(C'\fR is not used:
.PP
.Vb 1
\& nbdkit file disk.img \-\-filter=xor xor=rand:1984
.Ve
.PP
This filter does not currently support sparse plugins.  Trim
operations will fill the backing plugin with XORed zeroes (which makes
it easy to read out the "key", another reason why this is not secure).
.SH PARAMETERS
.IX Header "PARAMETERS"
.IP \fBxor=\fRVALUE 4
.IX Item "xor=VALUE"
The value to be XORed with the underlying data.  This is truncated or
extended to \f(CW\*(C`xorlen\*(C'\fR bytes.  Usually you want to specify this in hex
using the \f(CW\*(C`0x\*(C'\fR prefix.
.Sp
The value is big endian.  For example \f(CW\*(C`xor=0x123456\ xorlen=3\*(C'\fR will
XOR bytes as follows:
.Sp
.Vb 4
\& data:     A0 A1 A2 A3 A4 A5 A6
\& XOR with: 12 34 56 12 34 56 12
\&           ────────────────────
\& result:   B2 95 F4 B1 90 F3 B4
.Ve
.IP \fBxor=rand\fR 4
.IX Item "xor=rand"
.PD 0
.IP \fBxor=rand:\fRSEED 4
.IX Item "xor=rand:SEED"
.PD
XOR the underlying data with the output of a pseudo\-random number
generator (PRNG).  Optionally a seed for the PRNG may be given
(otherwise the seed is 0).
.Sp
The \f(CW\*(C`xor\*(C'\fR parameter is required.
.IP \fBxorlen=\fRLENBYTES 4
.IX Item "xorlen=LENBYTES"
The length of the XOR value, in bytes.  Any length from 1 to 8 is
supported.
.Sp
This parameter is required when using \f(CW\*(C`xor=VALUE\*(C'\fR and should not be
set for \f(CW\*(C`xor=rand\*(C'\fR.
.SH FILES
.IX Header "FILES"
.ie n .IP \fR\fI$filterdir\fR\fI/nbdkit\-xor\-filter.so\fR 4
.el .IP \fR\f(CI$filterdir\fR\fI/nbdkit\-xor\-filter.so\fR 4
.IX Item "$filterdir/nbdkit-xor-filter.so"
The filter.
.Sp
Use \f(CW\*(C`nbdkit \-\-dump\-config\*(C'\fR to find the location of \f(CW$filterdir\fR.
.SH VERSION
.IX Header "VERSION"
\&\f(CW\*(C`nbdkit\-xor\-filter\*(C'\fR first appeared in nbdkit 1.48.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-file\-plugin\fR\|(1),
\&\fBnbdkit\-luks\-filter\fR\|(1),
\&\fBnbdkit\-map\-filter\fR\|(1),
\&\fBnbdkit\-pattern\-plugin\fR\|(1),
\&\fBnbdkit\-random\-plugin\fR\|(1),
\&\fBnbdkit\-swab\-filter\fR\|(1),
\&\fBnbdkit\-filter\fR\|(3),
\&\fBnbdkit_parse_uint64_t\fR\|(3).
.SH AUTHORS
.IX Header "AUTHORS"
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
.IP \(bu 4
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.IP \(bu 4
Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
.IP \(bu 4
Neither the name of Red Hat nor the names of its contributors may be
used to endorse or promote products derived from this software without
specific prior written permission.
.PP
THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS \*(Aq\*(AqAS IS\*(Aq\*(Aq AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.