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 5.1.2 August 25, 2006 NetBSD 5.1.2
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