.\" Copyright 2009 Colin Percival
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.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 f
.Op Fl M Ar maxmem
.Op Fl m Ar maxmemfrac
.Op Fl t Ar maxtime
.Op Fl P
.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.
.Pp
If
.Fl P
is not given,
.Nm
reads passphrases from its controlling terminal, or failing that,
from stdin.  Prompts are only printed when
.Nm
is reading passphrases from some terminal.  If
.Fl P
is given, then
.Nm
does not print any prompts, and reads a passphrase from stdin.
.Sh OPTIONS
.Bl -tag -width "-m maxmemfrac"
.It Fl f
Force the decryption to proceed even if it is anticipated to
require an excessive amount of memory or CPU time.
.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 P
Always read passphrase from stdin, and do so only once even
when encrypting.
.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.