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CKSUM(1)                  BSD General Commands Manual                 CKSUM(1)

     cksum, md2, md4, md5, rmd160, sha1, sum -- display file checksums and
     block counts

     cksum [-n] [-a algorithm [-ptx] [-s string]] [-o 1|2]
           [file ... | -c [-w] [sumfile]]
     sum [-n] [-a algorithm [-ptx] [-s string]] [-o 1|2]
           [file ... | -c [-w] [sumfile]]
     md2 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]
     md4 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]
     md5 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]
     rmd160 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]
     sha1 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]

     The cksum utility writes to the standard output three whitespace
     separated fields for each input file.  These fields are a checksum CRC,
     the total number of octets in the file and the file name.  If no file
     name is specified, the standard input is used and no file name is

     The sum utility is identical to the cksum utility, except that it
     defaults to using historic algorithm 1, as described below.  It is
     provided for compatibility only.

     The md2, md4, md5, sha1, and rmd160 utilities compute cryptographic hash
     functions, and write to standard output the hexadecimal representation of
     the hash of their input.

     The options are as follows:

     -a algorithm
             When invoked as cksum, use the specified algorithm.  Valid
             algorithms are:

                   Algorithm    Bits    Description
                   CRC          32      Default CRC algorithm
                   MD2          128     MD2, per RFC1319
                   MD4          128     MD4, per RFC1320
                   MD5          128     MD5, per RFC1321
                   RMD160       160     RIPEMD-160
                   SHA1         160     SHA-1, per FIPS PUB 180-1
                   SHA256       256     SHA-2
                   SHA384       384     SHA-2
                   SHA512       512     SHA-2
                   old1         16      Algorithm 1, per -o 1
                   old2         16      Algorithm 2, per -o 2

     -c [sumfile]
             Verify (check) files against a list of checksums.  The list is
             read from sumfile, or from stdin if no filename is given.  E.g.
             first run
                   md5 *.tgz > MD5
                   sha1 *.tgz > SHA1
             to generate a list of MD5 checksums in MD5, then use the
             following command to verify them:
                   cat MD5 SHA1 | cksum -c
             If an error is found during checksum verification, an error
             message is printed, and the program returns an error code of 1.

     -o      Use historic algorithms instead of the (superior) default one.

             Algorithm 1 is the algorithm used by historic BSD systems as the
             sum(1) algorithm and by historic AT&T System V UNIX systems as
             the sum(1) algorithm when using the -r option.  This is a 16-bit
             checksum, with a right rotation before each addition; overflow is

             Algorithm 2 is the algorithm used by historic AT&T System V UNIX
             systems as the default sum(1) algorithm.  This is a 32-bit
             checksum, and is defined as follows:

                   s = sum of all bytes;
                   r = s % 2^16 + (s % 2^32) / 2^16;
                   cksum = (r % 2^16) + r / 2^16;

             Both algorithm 1 and 2 write to the standard output the same
             fields as the default algorithm except that the size of the file
             in bytes is replaced with the size of the file in blocks.  For
             historic reasons, the block size is 1024 for algorithm 1 and 512
             for algorithm 2.  Partial blocks are rounded up.

     -w      Print warnings about malformed checksum files when verifying
             checksums with -c.

     The following options apply only when using the one of the message digest

     -n      Print the hash and the filename in the normal sum output form,
             with the hash at the left and the filename following on the

     -p      Echo input from standard input to standard output, and append the
             selected message digest.

     -s string
             Print the hash of the given string string.

     -t      Run a built-in message digest time trial.

     -x      Run a built-in message digest test script.  The tests that are
             run are supposed to encompass all the various tests in the suites
             that accompany the algorithms' descriptions with the exception of
             the last test for the SHA-1 algorithm and the RIPEMD-160
             algorithm.  The last test for these is one million copies of the
             lower letter a.

     The default CRC used is based on the polynomial used for CRC error
     checking in the networking standard ISO/IEC 8802-3:1989.  The CRC
     checksum encoding is defined by the generating polynomial:

           G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
                x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1

     Mathematically, the CRC value corresponding to a given file is defined by
     the following procedure:

           The n bits to be evaluated are considered to be the coefficients of
           a  mod  2 polynomial M(x) of degree n-1.  These n bits are the bits
           from the file,  with  the  most  significant  bit  being  the  most
           significant  bit  of  the  first octet of the file and the last bit
           being the least significant bit of the last octet, padded with zero
           bits  (if  necessary)  to  achieve  an  integral  number of octets,
           followed by one or more octets representing the length of the  file
           as  a  binary  value,  least significant octet first.  The smallest
           number of octets capable of representing this integer are used.

           M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided
           by  G(x) using mod 2 division, producing a remainder R(x) of degree
           <= 31.

           The coefficients of R(x) are considered to be a 32-bit sequence.

           The bit sequence is complemented and the result is the CRC.

     The cksum and sum utilities exit 0 on success, and >0 if an error occurs.

     openssl(1), mtree(8)

     The default calculation is identical to that given in pseudo-code in the
     following ACM article.

     Dilip V. Sarwate, "Computation of Cyclic Redundancy Checks Via Table
     Lookup", Communications of the ACM, August 1988.

     R. Rivest, The MD2 Message-Digest Algorithm, RFC 1319.

     R. Rivest, The MD4 Message-Digest Algorithm, RFC 1186 and RFC 1320.

     R. Rivest, The MD5 Message-Digest Algorithm, RFC 1321.

     U.S. DOC/NIST, Secure Hash Standard, FIPS PUB 180-1.

     The cksum utility is expected to conform to IEEE Std 1003.1-2004

     The cksum utility appeared in 4.4BSD.  md5 was added in NetBSD 1.3.  The
     functionality for md2, md4, sha1, and rmd160 was added in NetBSD 1.6.
     Support for the SHA-2 algorithms (SHA256, SHA384, and SHA512) was added
     in NetBSD 3.0.  The functionality to verify checksum stored in a file
     (-c) first appeared in NetBSD 4.0.

BSD                              June 24, 2012                             BSD