.\"	$OpenBSD: sha1.1,v 1.34 2014/01/08 16:12:44 jmc Exp $
.\"
.\" Copyright (c) 2003, 2004, 2006 Todd C. Miller <Todd.Miller@courtesan.com>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
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.\" copyright notice and this permission notice appear in all copies.
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\" Sponsored in part by the Defense Advanced Research Projects
.\" Agency (DARPA) and Air Force Research Laboratory, Air Force
.\" Materiel Command, USAF, under agreement number F39502-99-1-0512.
.\"
.Dd $Mdocdate: January 8 2014 $
.Dt SHA1 1
.Os
.Sh NAME
.Nm sha1
.Nd calculate a message digest (checksum) for a file
.Sh SYNOPSIS
.Nm sha1
.Op Fl bpqrtx
.Op Fl c Op Ar checklist ...
.Op Fl h Ar hashfile
.Op Fl s Ar string
.Op Ar
.Sh DESCRIPTION
.Nm
takes as input a message of arbitrary length and produces
as output a 160-bit message digest (checksum) of the input.
It is conjectured that it is computationally infeasible to produce
two messages having the same message digest (a collision),
or to produce any message having a given prespecified target message digest.
However, researchers have developed theoretical attacks that significantly
reduce the amount of time needed to find a collision in SHA-1.
The use of other message digest functions, such as
.Xr sha256 1 ,
is now preferred.
.Pp
The SHA-1 algorithm is intended for digital signature applications,
where a large file must be "compressed" in a secure manner before
being encrypted with a private (secret) key under a public-key
cryptosystem such as RSA.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl b
Output checksums in base64 notation, not hexadecimal.
.It Fl c Op Ar checklist ...
Compares all checksums contained in the file
.Ar checklist
with newly computed checksums for the corresponding files.
Output consists of the digest used, the file name,
and an OK or FAILED for the result of the comparison.
This will validate any of the supported checksums (see
.Xr cksum 1 ) .
If no file is given, stdin is used.
.It Fl h Ar hashfile
Place the checksum into
.Ar hashfile
instead of stdout.
.It Fl p
Echoes stdin to stdout and appends the
checksum to stdout.
.It Fl q
Only print the checksum (quiet mode).
.It Fl r
Reverse the format of the hash algorithm output, making
it match the output format used by
.Xr cksum 1 .
.It Fl s Ar string
Prints a checksum of the given
.Ar string .
.It Fl t
Runs a built-in time trial.
Specifying
.Fl t
multiple times results in the number of rounds being multiplied
by 10 for each additional flag.
.It Fl x
Runs a built-in test script.
.El
.Pp
The checksum of each file listed on the command line is printed
after the options are processed.
.Pp
The
.Nm
command is shorthand for:
.Bd -literal -offset indent
$ cksum -a sha1
.Ed
.Pp
The
.Xr cksum 1
command can also be used to compute digests from the SHA-2 family:
sha256, sha384 and sha512.
.Sh EXIT STATUS
.Ex -std sha1
.Sh SEE ALSO
.Xr cksum 1 ,
.Xr md5 1 ,
.Xr sha256 1
.Rs
.%A X. Wang
.%A Y. Yin
.%A H. Yu
.%D 2005
.%J Crypto
.%T Finding Collisions in the Full SHA-1
.Re
.Sh STANDARDS
.Rs
.%A J. Burrows
.%O FIPS PUB 180-1
.%T The Secure Hash Standard
.Re
.Pp
.Rs
.%A D. Eastlake
.%A P. Jones
.%D September 2001
.%R RFC 3174
.%T US Secure Hash Algorithm 1 (SHA1)
.Re
.Sh CAVEATS
Theoretical attacks that significantly reduce the amount of time needed
to find a collision in
.Em SHA-1
have been developed.
The use of
.Xr sha256 1
is recommended instead.