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.\" $FreeBSD$
.Dd January 7, 2017
.Dt MD5 1
.Os
.Sh NAME
.Nm md5 , sha1 , sha256 , sha384 , sha512 , sha512t256 , rmd160 ,
.Nm skein256 , skein512 , skein1024
.Nd calculate a message-digest fingerprint (checksum) for a file
.Sh SYNOPSIS
.Nm md5
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Nm sha1
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Nm sha256
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Nm sha384
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Nm sha512
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Nm sha512t256
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Nm rmd160
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Nm skein256
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Nm skein512
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Nm skein1024
.Op Fl pqrtx
.Op Fl c Ar string
.Op Fl s Ar string
.Op Ar
.Sh DESCRIPTION
The
.Nm md5 , sha1 , 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.
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 , SHA-384 , SHA-512, RIPEMD-160,
and
.Tn 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
.Tn RSA .
.Pp
.Tn MD5
has been completely broken as far as finding collisions is
concerned, and should not be relied upon to produce unique outputs.
This also means that
.Tn MD5
should not be used as part of a cryptographic signature scheme.
At the current time (2014-05-17) there is no publicly known method to
.Dq reverse
MD5, i.e., to find an input given a hash value.
.Pp
.Tn SHA-1
currently (2014-05-17) has no known collisions, but an attack has been
found which is faster than a brute-force search, placing the security of
.Tn SHA-1
in doubt.
.Pp
.Tn SHA-512t256
is a version of
.Tn SHA-512
truncated to only 256 bits.
On 64-bit hardware, this algorithm is approximately 50% faster than
.Tn SHA-256
but with the same level of security.
The hashes are not interchangeable.
.Pp
It is recommended that all new applications use
.Tn SHA-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 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.
.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.
.It Fl x
Run a built-in test script.
.El
.Sh EXIT STATUS
The
.Nm md5 , sha1 , 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 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 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 .