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scrypt.1
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scrypt.1
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.\" Copyright 2009 Colin Percival
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. 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.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' 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 THE AUTHOR 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.
.Dd @DATE@
.Dt SCRYPT 1
.Os
.Sh NAME
.Nm scrypt
.Nd encrypt and decrypt files.
.Sh SYNOPSIS
.Nm
.Brq Cm enc | Cm dec
.Op Fl M Ar maxmem
.Op Fl m Ar maxmemfrac
.Op Fl t Ar maxtime
.Ar infile
.Op Ar outfile
.Nm
.Fl -version
.Sh DESCRIPTION
.Nm Cm enc
encrypts
.Ar infile
and writes the result to
.Ar outfile
if specified, or the standard output otherwise.
The user will be prompted to enter a passphrase (twice) to
be used to generate a derived encryption key.
.Pp
.Nm Cm dec
decrypts
.Ar infile
and writes the result to
.Ar outfile
if specified, or the standard output otherwise.
The user will be prompted to enter the passphrase used at
encryption time to generate the derived encryption key.
.Sh OPTIONS
.Bl -tag -width "-m maxmemfrac"
.It Fl M Ar maxmem
Use at most
.Ar maxmem
bytes of RAM to compute the derived encryption key.
.It Fl m Ar maxmemfrac
Use at most the fraction
.Ar maxmemfrac
of the available RAM to compute the derived encryption key.
.It Fl t Ar maxtime
Use at most
.Ar maxtime
seconds of CPU time to compute the derived encryption key.
.It Fl -version
Print version of scrypt, and exit.
.El
.Pp
In
.Nm Cm enc ,
the memory and CPU time limits are enforced by picking
appropriate parameters to the
.Nm
key derivation function.
In
.Nm Cm dec ,
the memory and CPU time limits are enforced by exiting with
an error if decrypting the file would require too much memory
or CPU time.
.Sh EXIT STATUS
The
.Nm
utility exits 0 on success, and >0 if an error occurs.
.Pp
Note that if the input encrypted file is corrupted,
.Nm Cm dec
may produce output prior to determining that the input
was corrupt and exiting with a non-zero status; so
users should direct the output to a safe location and
check the exit status of
.Nm
before using the decrypted data.
.Sh SEE ALSO
.Rs
.%A "Colin Percival"
.%T "Stronger Key Derivation via Sequential Memory-Hard Functions"
.%O "Presented at BSDCan'09"
.%D "May 2009"
.Re
.Sh HISTORY
The
.Nm
utility was written in May 2009 by Colin Percival as a
demonstration of the
.Nm
key derivation function.
The
.Nm
key derivation function was invented in March 2009 by Colin
Percival in order to allow key files from the
.Nm tarsnap
backup system to be passphrase protected.