path: root/sbin/md5/md5.1

.\" $FreeBSD$
.Dd Feb 5, 2022
.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
.Nm md5sum
.Op Fl pqrtx
.Op Fl c Ar file
.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
Make the
.Nm -sum
programs separate hash and digest with a blank followed by an asterisk instead
of by 2 blank characters for full compatibility with the output generated by the
coreutils versions of these programs.
.It Fl c Ar string
If the program was called with a name that does not end in
.Nm sum ,
compare the digest of the file against this string.
.Pq Note that this option is not yet useful if multiple files are specified.
.It Fl c Ar file
If the program was called with a name that does end in
.Nm sum ,
the file passed as argument must contain digest lines generated by the same
digest algorithm with or without the
.Fl r
option
.Pq i.e. in either classical BSD format or in GNU coreutils format .
A line with the file name followed by a colon
.Dq ":"
and either OK or FAILED is written for each well-formed line in the digest file.
If applicable, the number of failed comparisons and the number of lines that were
skipped since they were not well-formed are printed at the end.
The
.Fl q
option can be used to quiesce the output unless there are mismatched entries in
the digest.
.Pp
.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
.Pd
The
.Nm -sum
variants put 2 blank characters between hash and file name for full compatibility 
with the coreutils versions of these commands.
.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
.Pp
If invoked with a name ending in
.Nm -sum
the
.Fl c
option does not compare against a hash string passed as parameter.
Instead, it expects a digest file, as created under the name
.Pa digest
for
.Pa /boot/loader.conf
in the example above.
.Bd -literal -offset indent
$ md5 -c digest /boot/loader.conf
/boot/loader.conf: OK
.Ed
.Pp
The digest file may contain any number of lines in the format generated with or without the
.Fl r
option
.Pq i.e. in either classical BSD format or in GNU coreutils format .
If a hash value does not match the file, FAILED is printed instead of OK.
.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 https://www.nist.gov/publications/secure-hash-standard-shs
.Pp
The RIPEMD-160 page:
.Pa https://homes.esat.kuleuven.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 option functionality is 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 .