.\" $FreeBSD: src/sbin/md5/md5.1,v 1.24 2005/03/10 09:56:39 cperciva Exp $
.Dd January 21, 2010
.Dt MD5 1
.Os
.Sh NAME
.Nm md5 ,
.Nm sha1 ,
.Nm sha256 ,
.Nm rmd160
.Nd calculate a message-digest fingerprint (checksum) for a file
.Sh SYNOPSIS
.Nm md5
.Op Fl pqrtx
.Op Fl b Ar offset
.Op Fl e Ar offset
.Op Fl s Ar string
.Op Ar
.Nm sha1
.Op Fl pqrtx
.Op Fl b Ar offset
.Op Fl e Ar offset
.Op Fl s Ar string
.Op Ar
.Nm sha256
.Op Fl pqrtx
.Op Fl b Ar offset
.Op Fl e Ar offset
.Op Fl s Ar string
.Op Ar
.Nm rmd160
.Op Fl pqrtx
.Op Fl b Ar offset
.Op Fl e Ar offset
.Op Fl s Ar string
.Op Ar
.Sh DESCRIPTION
The
.Nm md5 ,
.Nm sha1 ,
.Nm sha256
and
.Nm rmd160
utilities take as input a message of arbitrary length and produce as
output a
.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
.Tn MD5 , SHA-1, SHA-256
and
.Tn RIPEMD-160
algorithms are 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
.Tn RSA .
.Pp
.Tn 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
.Tn 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 hexadecimal checksum of each file listed on the command line is printed
after the options are processed.
.Bl -tag -width indent
.It Fl b Ar offset
When processing file(s), use the specified begin and/or end (below) instead
of processing each file in its entirety.
Either option can be omitted.
Both begin- and end-offsets can be specified as just a number (of bytes) or
be followed by K, M, or G to mean that the number is to be multiplied by
1024 once, twice, or thrice respectively.
For example, to start at 512, you can use
.Fl b Ar 512
or
.Fl b Ar 0.5K .
.Pp
The use of offsets is implemented using
.Fn mmap
and will only work on regular files and mmap-able devices.
.Pp
If the beginning offset is negative, its absolute value is subtracted
from the file's size.
Zero thus means the very beginning of each file,
which is also the default if the option is omitted entirely.
.It Fl e Ar offset
If the end-offset is not positive, its absolute value is subtracted
from the file's size.
Zero thus means the very end of each file,
which is also the default if the option is omitted entirely.
.It Fl s Ar string
Print a checksum of the given
.Ar string .
.It Fl p
Echo stdin to stdout and append the checksum to stdout.
.It Fl q
Quiet mode - only the checksum 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 DIAGNOSTICS
The
.Nm md5 ,
.Nm sha1 ,
.Nm sha256
and
.Nm rmd160
utilities exit 0 on success, and
.Dv EX_NOINPUT Pq 66
if at least one of the input files could not be read or
invalid offsets were specified.
A mistake with command line arguments results in
.Dv EX_USAGE Pq 64 .
.Sh SEE ALSO
.Xr cksum 1 ,
.Xr mmap 2 ,
.Xr md5 3 ,
.Xr ripemd 3 ,
.Xr sha 3
.Rs
.%A R. Rivest
.%T The MD5 Message-Digest Algorithm
.%O RFC 1321
.Re
.Rs
.%A J. Burrows
.%T The Secure Hash Standard
.%O FIPS PUB 180-1
.Re
.Rs
.%A D. Eastlake and P. Jones
.%T US Secure Hash Algorithm 1
.%O RFC 3174
.Re
.Pp
RIPEMD-160 is part of the ISO draft standard
.Qq ISO/IEC DIS 10118-3
on dedicated hash functions.
.Pp
Secure Hash Standard (SHS):
.Pa http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf .
.Pp
The RIPEMD-160 page:
.Pa http://www.esat.kuleuven.ac.be/~bosselae/ripemd160.html .
.Sh ACKNOWLEDGMENTS
This program is placed in the public domain for free general use by
RSA Data Security.
.Pp
Support for SHA-1 and RIPEMD-160 has been added by
.An Oliver Eikemeier Aq Mt eik@FreeBSD.org .