b33d1898c1
The previous changes that added support for the coreutils -c option modified the output generated by passing -r to match that of the coreutils versions. The difference is that coreutils separates the hash from the file name by two blanks " " (or a blank followed by an asterisk " *" with the -b option denoting). While most scripts or users will not notice the difference, it might be considered a violation of POLA and this commit reverts the change for the non-sum programs. These will print a single blank " " as the separator, as they die before the previous commit. In order to still generate output that is identical to that of the coreutils programs, this commit generates the " " or " *" separator used by them for the -sum versions, depending on the presence of the -b option. MFC after: 3 days
257 lines
7.1 KiB
Groff
257 lines
7.1 KiB
Groff
.\" $FreeBSD$
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.Dd June 29, 2021
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.Dt MD5 1
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.Os
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.Sh NAME
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.Nm md5 , sha1 , sha224 , sha256 , sha384 , sha512 , sha512t256 , rmd160 ,
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.Nm skein256 , skein512 , skein1024 ,
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.Nm md5sum , sha1sum , sha224sum , sha256sum , sha384sum , sha512sum ,
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.Nm sha512t256sum , rmd160sum , skein256sum , skein512sum , skein1024sum
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.Nd calculate a message-digest fingerprint (checksum) for a file
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.Sh SYNOPSIS
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.Nm
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.Op Fl pqrtx
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.Op Fl c Ar string
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.Op Fl s Ar string
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.Op Ar
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.Pp
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.Nm md5sum
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.Op Fl pqrtx
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.Op Fl c Ar file
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.Op Fl s Ar string
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.Op Ar
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.Pp
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(All other hashes have the same options and usage.)
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.Sh DESCRIPTION
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The
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.Nm md5 , sha1 , sha224 , sha256 , sha384 , sha512 , sha512t256 , rmd160 ,
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.Nm skein256 , skein512 ,
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and
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.Nm skein1024
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utilities take as input a message of arbitrary length and produce as
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output a
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.Dq fingerprint
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or
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.Dq message digest
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of the input.
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The
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.Nm md5sum , sha1sum , sha224sum , sha256sum , sha384sum , sha512sum ,
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.Nm sha512t256sum , rmd160sum , skein256sum , skein512sum ,
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and
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.Nm skein1024sum
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utilities do the same, but default to the reversed format of
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the
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.Fl r
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flag.
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It is conjectured that it is computationally infeasible to
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produce two messages having the same message digest, or to produce any
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message having a given prespecified target message digest.
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The SHA-224 , SHA-256 , SHA-384 , SHA-512, RIPEMD-160,
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and SKEIN
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algorithms are intended for digital signature applications, where a
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large file must be
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.Dq compressed
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in a secure manner before being encrypted with a private
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(secret)
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key under a public-key cryptosystem such as RSA.
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.Pp
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The MD5 and SHA-1 algorithms have been proven to be vulnerable to practical
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collision attacks and should not be relied upon to produce unique outputs,
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.Em nor should they be used as part of a cryptographic signature scheme.
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As of 2017-03-02, there is no publicly known method to
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.Em reverse
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either algorithm, i.e., to find an input that produces a specific
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output.
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.Pp
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SHA-512t256 is a version of SHA-512 truncated to only 256 bits.
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On 64-bit hardware, this algorithm is approximately 50% faster than SHA-256 but
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with the same level of security.
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The hashes are not interchangeable.
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.Pp
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It is recommended that all new applications use SHA-512 or SKEIN-512
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instead of one of the other hash functions.
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.Pp
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The following options may be used in any combination and must
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precede any files named on the command line.
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The hexadecimal checksum of each file listed on the command line is printed
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after the options are processed.
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.Bl -tag -width indent
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.It Fl b
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Make the
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.Nm -sum
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programs separate hash and digest with a blank followed by an asterisk instead
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of by 2 blank characters for full compatibility with the output generated by the
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coreutils versions of these programs.
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.It Fl c Ar string
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If the program was called with a name that does not end in
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.Nm sum ,
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compare the digest of the file against this string.
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.Pq Note that this option is not yet useful if multiple files are specified.
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.It Fl c Ar file
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If the program was called with a name that does end in
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.Nm sum ,
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the file passed as argument must contain digest lines generated by the same
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digest algorithm with or without the
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.Fl r
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option
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.Pq i.e. in either classical BSD format or in GNU coreutils format .
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A line with the file name followed by a colon
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.Dq ":"
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and either OK or FAILED is written for each well-formed line in the digest file.
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If applicable, the number of failed comparisons and the number of lines that were
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skipped since they were not well-formed are printed at the end.
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The
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.Fl q
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option can be used to quiesce the output unless there are mismatched entries in
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the digest.
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.Pp
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.It Fl s Ar string
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Print a checksum of the given
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.Ar string .
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.It Fl p
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Echo stdin to stdout and append the checksum to stdout.
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.It Fl q
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Quiet mode \(em only the checksum is printed out.
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Overrides the
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.Fl r
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option.
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.It Fl r
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Reverses the format of the output.
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This helps with visual diffs.
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Does nothing
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when combined with the
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.Fl ptx
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options.
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.It Fl t
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Run a built-in time trial.
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For the
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.Nm -sum
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versions, this is a nop for compatibility with coreutils.
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.It Fl x
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Run a built-in test script.
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.El
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.Sh EXIT STATUS
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The
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.Nm md5 , sha1 , sha224 , sha256 , sha512 , sha512t256 , rmd160 ,
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.Nm skein256 , skein512 ,
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and
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.Nm skein1024
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utilities exit 0 on success,
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1 if at least one of the input files could not be read,
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and 2 if at least one file does not have the same hash as the
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.Fl c
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option.
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.Sh EXAMPLES
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Calculate the MD5 checksum of the string
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.Dq Hello .
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.Bd -literal -offset indent
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$ md5 -s Hello
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MD5 ("Hello") = 8b1a9953c4611296a827abf8c47804d7
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.Ed
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.Pp
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Same as above, but note the absence of the newline character in the input
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string:
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.Bd -literal -offset indent
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$ echo -n Hello | md5
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8b1a9953c4611296a827abf8c47804d7
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.Ed
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.Pp
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Calculate the checksum of multiple files reversing the output:
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.Bd -literal -offset indent
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$ md5 -r /boot/loader.conf /etc/rc.conf
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ada5f60f23af88ff95b8091d6d67bef6 /boot/loader.conf
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d80bf36c332dc0fdc479366ec3fa44cd /etc/rc.conf
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.Pd
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The
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.Nm -sum
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variants put 2 blank characters between hash and file name for full compatibilty
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with the coreutils versions of these commands.
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.Ed
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.Pp
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Write the digest for
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.Pa /boot/loader.conf
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in a file named
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.Pa digest .
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Then calculate the checksum again and validate it against the checksum string
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extracted from the
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.Pa digest
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file:
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.Bd -literal -offset indent
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$ md5 /boot/loader.conf > digest && md5 -c $(cut -f2 -d= digest) /boot/loader.conf
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MD5 (/boot/loader.conf) = ada5f60f23af88ff95b8091d6d67bef6
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.Ed
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.Pp
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Same as above but comparing the digest against an invalid string
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.Pq Dq randomstring ,
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which results in a failure.
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.Bd -literal -offset indent
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$ md5 -c randomstring /boot/loader.conf
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MD5 (/boot/loader.conf) = ada5f60f23af88ff95b8091d6d67bef6 [ Failed ]
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.Ed
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.Pp
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If invoked with a name ending in
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.Nm -sum
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the
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.Fl c
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option does not compare against a hash string passed as parameter.
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Instead, it expects a digest file, as created under the name
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.Pa digest
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for
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.Pa /boot/loader.conf
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in the example above.
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.Bd -literal -offset indent
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$ md5 -c digest /boot/loader.conf
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/boot/loader.conf: OK
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.Ed
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.Pp
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The digest file may contain any number of lines in the format generated with or without the
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.Fl r
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option
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.Pq i.e. in either classical BSD format or in GNU coreutils format .
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If a hash value does not match the file, FAILED is printed instead of OK.
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.Sh SEE ALSO
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.Xr cksum 1 ,
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.Xr md5 3 ,
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.Xr ripemd 3 ,
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.Xr sha 3 ,
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.Xr sha256 3 ,
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.Xr sha384 3 ,
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.Xr sha512 3 ,
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.Xr skein 3
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.Rs
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.%A R. Rivest
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.%T The MD5 Message-Digest Algorithm
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.%O RFC1321
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.Re
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.Rs
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.%A J. Burrows
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.%T The Secure Hash Standard
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.%O FIPS PUB 180-2
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.Re
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.Rs
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.%A D. Eastlake and P. Jones
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.%T US Secure Hash Algorithm 1
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.%O RFC 3174
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.Re
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.Pp
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RIPEMD-160 is part of the ISO draft standard
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.Qq ISO/IEC DIS 10118-3
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on dedicated hash functions.
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.Pp
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Secure Hash Standard (SHS):
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.Pa http://csrc.nist.gov/cryptval/shs.html .
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.Pp
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The RIPEMD-160 page:
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.Pa http://www.esat.kuleuven.ac.be/~bosselae/ripemd160.html .
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.Sh BUGS
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All of the utilities that end in
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.Sq sum
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are intended to be compatible with the GNU coreutils programs.
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However, the long option functionality is not provided.
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.Sh ACKNOWLEDGMENTS
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This program is placed in the public domain for free general use by
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RSA Data Security.
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.Pp
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Support for SHA-1 and RIPEMD-160 has been added by
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.An Oliver Eikemeier Aq Mt eik@FreeBSD.org .
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