.\"	$OpenBSD: md5.1,v 1.31 2010/07/13 22:34:45 tedu 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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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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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: July 13 2010 $
.Dt MD5 1
.Os
.Sh NAME
.Nm md5
.Nd calculate a message-digest fingerprint (checksum) for a file
.Sh SYNOPSIS
.Nm md5
.Op Fl bpqrtx
.Op Fl c Op Ar checklist ...
.Op Fl s Ar string
.Op Ar
.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 sha256 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 Fl b
Output checksums in base64 notation, not hexadecimal.
.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 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 MD5 sum of each file listed on the command line is printed after the
options are processed.
.Pp
.Ex -std md5
.Sh SEE ALSO
.Xr cksum 1 ,
.Xr sha1 1 ,
.Xr sha256 1
.Rs
.%A R. Rivest
.%T The MD5 Message-Digest Algorithm
.%O RFC 1321
.Re
.Sh CAVEATS
Since collisions have been found for
.Em MD5 ,
the use of
.Xr sha256 1
is recommended instead.