sbin/md5/md5.1

.\" $FreeBSD$
.Dd May 19, 2021
.Dt MD5 1
.Os
.Sh NAME
.Nm md5 , sha1 , sha224 , sha256 , sha384 , sha512 , sha512t256 , rmd160 ,
.Nm skein256 , skein512 , skein1024 ,
.Nm md5sum , sha1sum , sha224sum , sha256sum , sha384sum , sha512sum ,
.Nm sha512t256sum , rmd160sum , skein256sum , skein512sum , skein1024sum
.Nd calculate a message-digest fingerprint (checksum) for a file
.Sh SYNOPSIS
.Nm
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Pp
(All other hashes have the same options and usage.)
.Sh DESCRIPTION
The
.Nm md5 , sha1 , sha224 , sha256 , sha384 , sha512 , sha512t256 , rmd160 ,
.Nm skein256 , skein512 ,
and
.Nm skein1024
utilities take as input a message of arbitrary length and produce as
output a
.Dq fingerprint
or
.Dq message digest
of the input.
The
.Nm md5sum , sha1sum , sha224sum , sha256sum , sha384sum , sha512sum ,
.Nm sha512t256sum , rmd160sum , skein256sum , skein512sum ,
and
.Nm skein1024sum
utilities do the same, but default to the reversed format of
the
.Fl r
flag.
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 SHA-224 , SHA-256 , SHA-384 , SHA-512, RIPEMD-160,
and SKEIN
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 RSA.
.Pp
The MD5 and SHA-1 algorithms have been proven to be vulnerable to practical
collision attacks and should not be relied upon to produce unique outputs,
.Em nor should they be used as part of a cryptographic signature scheme.
As of 2017-03-02, there is no publicly known method to
.Em reverse
either algorithm, i.e., to find an input that produces a specific
output.
.Pp
SHA-512t256 is a version of SHA-512 truncated to only 256 bits.
On 64-bit hardware, this algorithm is approximately 50% faster than SHA-256 but
with the same level of security.
The hashes are not interchangeable.
.Pp
It is recommended that all new applications use SHA-512 or SKEIN-512
instead of one of the other hash functions.
.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
Ignored for compatibility with the coreutils
.Nm -sum
programs.
.It Fl c Ar string
Compare the digest of the file against this string.
.Pq Note that this option is not yet useful if multiple files are specified.
This option causes an error in for the
.Nm -sum
programs because it check the checksums listed in a file for the coreutils
.Nm -sum
programs that is not yet implemented.
.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 \(em 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.
For the
.Nm -sum
versions, this is a nop for compatibility with coreutils.
.It Fl x
Run a built-in test script.
.El
.Sh EXIT STATUS
The
.Nm md5 , sha1 , sha224 , sha256 , sha512 , sha512t256 , rmd160 ,
.Nm skein256 , skein512 ,
and
.Nm skein1024
utilities exit 0 on success,
1 if at least one of the input files could not be read,
and 2 if at least one file does not have the same hash as the
.Fl c
option.
.Sh EXAMPLES
Calculate the MD5 checksum of the string
.Dq Hello .
.Bd -literal -offset indent
$ md5 -s Hello
MD5 ("Hello") = 8b1a9953c4611296a827abf8c47804d7
.Ed
.Pp
Same as above, but note the absence of the newline character in the input
string:
.Bd -literal -offset indent
$ echo -n Hello | md5
8b1a9953c4611296a827abf8c47804d7
.Ed
.Pp
Calculate the checksum of multiple files reversing the output:
.Bd -literal -offset indent
$ md5 -r /boot/loader.conf /etc/rc.conf
ada5f60f23af88ff95b8091d6d67bef6 /boot/loader.conf
d80bf36c332dc0fdc479366ec3fa44cd /etc/rc.conf
.Ed
.Pp
Write the digest for
.Pa /boot/loader.conf
in a file named
.Pa digest .
Then calculate the checksum again and validate it against the checksum string
extracted from the
.Pa digest
file:
.Bd -literal -offset indent
$ md5 /boot/loader.conf > digest && md5 -c $(cut -f2 -d= digest) /boot/loader.conf
MD5 (/boot/loader.conf) = ada5f60f23af88ff95b8091d6d67bef6
.Ed
.Pp
Same as above but comparing the digest against an invalid string
.Pq Dq randomstring ,
which results in a failure.
.Bd -literal -offset indent
$ md5 -c randomstring /boot/loader.conf
MD5 (/boot/loader.conf) = ada5f60f23af88ff95b8091d6d67bef6 [ Failed ]
.Ed
.Sh SEE ALSO
.Xr cksum 1 ,
.Xr md5 3 ,
.Xr ripemd 3 ,
.Xr sha 3 ,
.Xr sha256 3 ,
.Xr sha384 3 ,
.Xr sha512 3 ,
.Xr skein 3
.Rs
.%A R. Rivest
.%T The MD5 Message-Digest Algorithm
.%O RFC1321
.Re
.Rs
.%A J. Burrows
.%T The Secure Hash Standard
.%O FIPS PUB 180-2
.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/cryptval/shs.html .
.Pp
The RIPEMD-160 page:
.Pa http://www.esat.kuleuven.ac.be/~bosselae/ripemd160.html .
.Sh BUGS
All of the utilities that end in
.Sq sum
are intended to be compatible with the GNU coreutils programs.
However, the long arguments and the
.Fl -check
functionality are not provided.
.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 .