.\"	$OpenBSD: md5.1,v 1.20 2004/08/24 21:22:25 tom Exp $
.\"
.\" Copyright (c) 2003, 2004 Todd C. Miller <Todd.Miller@courtesan.com>
.\"
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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 April 30, 2004
.Dt MD5 1
.Os
.Sh NAME
.Nm md5
.Nd calculate a message-digest fingerprint (checksum) for a file
.Sh SYNOPSIS
.Nm md5
.Oo
.Fl p | t | x |
.Fl c Oo Ar checklist ... Oc |
.Fl s Ar string |
.Ar file ...
.Oc
.Sh DESCRIPTION
.Nm
takes as input a message of arbitrary length and produces
as output a 128-bit "fingerprint" or "message digest" of the input.
It was conjectured that it would be 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, collisions have now been produced for
.Em MD5 ,
so the use of other message digest functions, such as
.Xr sha1 1 ,
is now preferred.
.Pp
The
.Em MD5
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
.Em RSA .
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Xo
.Fl c
.Op Ar checklist ...
.Xc
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 p
Echoes stdin to stdout and appends the
.Em MD5
sum to stdout.
.It Fl s Ar string
Prints a checksum of the given
.Ar string .
.It Fl t
Runs a built-in time trial.
.It Fl x
Runs a built-in test script.
.El
.Pp
The MD5 sum of each file listed on the command line is printed after the
options are processed.
.Sh SEE ALSO
.Xr cksum 1 ,
.Xr rmd160 1 ,
.Xr sha1 1
.Rs
.%A R. Rivest
.%T The MD5 Message-Digest Algorithm
.%O RFC 1321
.Re
.Sh BUGS
Since collisions have been found for
.Em MD5 ,
the use of
.Xr sha1 1
is recommended instead.