CKSUM(1)                NetBSD General Commands Manual                CKSUM(1)

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

SYNOPSIS
     cksum [-nw] [-a algorithm | -c [file] | [-o 1 | 2]] [file ...]
     sum [-w] [-c [file]] [file ...]
     md2 [-nw] [-c [file] | -p | -t | -x | -s string] [file ...]
     md4 [-nw] [-c [file] | -p | -t | -x | -s string] [file ...]
     md5 [-nw] [-c [file] | -p | -t | -x | -s string] [file ...]
     sha1 [-nw] [-c [file] | -p | -t | -x | -s string] [file ...]
     rmd160 [-nw] [-c [file] | -p | -t | -x | -s string] [file ...]

DESCRIPTION
     The cksum utility writes to the standard output three whitespace sepa-
     rated 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 written.

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

     The md5 utility takes as input a message of arbitrary length and produces
     as output a 128-bit ``fingerprint'' or ``message digest'' of the input.
     It is conjectured that it is computationally infeasible to product two
     messages having the same message digest, or to produce any message having
     a given prespecified target message digest.  The MD5 algorithm is
     intended for digital signature applications, where a large file must be
     ``compressed'' in a secure manner before being encrypted with a private
     (secret) key under a public-key encryption system such as RSA.

     The md2 and md4 utilities behave in exactly the same manner as md5 but
     use different algorithms.

     The sha1 and rmd160 utilities also produce message digests, however the
     output from these two programs is 160 bits in length, as opposed to 128.

     The options are as follows:

     -a algorithm
             When invoked as cksum, use the specified algorithm.  Valid algo-
             rithms are MD2, MD4, MD5, SHA1, RMD160, SHA256, SHA384, SHA512,
             CRC, old1, and old2.  Old1 and old2 are equal to -o 1 and -o 2,
             respectively.  The default is CRC.

     -c [file]
             Verify (check) files against a list of checksums.  The list is
             read from file, 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 follow-
             ing command to verify them:
                   cat MD5 SHA1 | cksum -c
             If an error is found during checksum verification, an error mes-
             sage 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
             discarded.

             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 check-
             sum, 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
     algorithms:

     -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
             right.

     -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 algo-
             rithm.  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 check-
     ing 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 signif-
           icant 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.

SEE ALSO
     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.

STANDARDS
     The cksum utility is expected to conform to IEEE Std 1003.2-1992
     (``POSIX.2'').

HISTORY
     The cksum utility appeared in 4.4BSD.  The functionality for md2, md4,
     sha1, and rmd160 was added in NetBSD 1.6.  Support for sha2 was added in
     NetBSD 3.0.  The functionality to verify checksum stored in a file (-c)
     first appeared in NetBSD 4.0.

NetBSD 5.0.1                    August 25, 2006                   NetBSD 5.0.1

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