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.\" $FreeBSD$
.Dd February 14, 1994
.Dt MD5 1
.Os
.Sh NAME
.Nm md5
.Nd calculate a message-digest fingerprint (checksum) for a file
.Sh SYNOPSIS
.Nm
.Op Fl pqrtx
.Op Fl s Ar string
.Op Ar
.Sh DESCRIPTION
.Nm Md5
takes as input a message of arbitrary length and produces
as output a 128-bit
.Dq fingerprint
or
.Dq message digest
of the input.
It is conjectured that it is computationally infeasible to
produce two messages having the same message digest, or to produce any
message having a given prespecified target message digest.
The MD5 algorithm is intended for digital signature applications, where a
large file must be
.Dq compressed
in a secure manner before being encrypted with a private
(secret)
key under a public-key cryptosystem such as
.Em RSA .
.Pp
MD5 has not yet (2001-09-03) been broken, but sufficient attacks have been
made that its security is in some doubt.
The attacks on MD5
are in the nature of finding
.Dq collisions
\(em that is, multiple
inputs which hash to the same value; it is still unlikely for an attacker
to be able to determine the exact original input given a hash value.
.Pp
The following options may be used in any combination and must
precede any files named on the command line.
The MD5
sum of each file listed on the command line is printed after the options
are processed.
.Bl -tag -width indent
.It Fl s Ar string
Print a checksum of the given
.Ar string .
.It Fl p
Echo stdin to stdout and appends the MD5 sum to stdout.
.It Fl q
Quiet mode - only the MD5 sum is printed out.
Overrides the
.Fl r
option.
.It Fl r
Reverses the format of the output.
This helps with visual diffs.
Does nothing
when combined with the
.Fl ptx
options.
.It Fl t
Run a built-in time trial.
.It Fl x
Run a built-in test script.
.El
.Sh SEE ALSO
.Xr cksum 1
.Rs
.%A R. Rivest
.%T The MD5 Message-Digest Algorithm
.%O RFC1321
.Re
.Sh ACKNOWLEDGMENTS
This program is placed in the public domain for free general use by
RSA Data Security.
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