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

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

cksum[-n] [-m|-1|-2|-4|-5|-6| [-o1|2]] [file ...]sum[file ...]md2[-n] [-p] [-t] [-x] [-sstring] [file ...]md4[-n] [-p] [-t] [-x] [-sstring] [file ...]md5[-n] [-p] [-t] [-x] [-sstring] [file ...]sha1[-n] [-p] [-t] [-x] [-sstring] [file ...]rmd160[-n] [-p] [-t] [-x] [-sstring] [file ...]DESCRIPTION

Thecksumutility 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. Thesumutility is identical to thecksumutility, except that it defaults to using historic algorithm 1, as described below. It is pro- vided for compatibility only. Themd5utility 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 asRSA. Themd2andmd4utilities behave in exactly the same manner asmd5but use different algorithms. Thesha1andrmd160utilities 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:-1Use the SHA1 algorithm rather than the default one.-2Use the MD2 algorithm rather than the default one.-4Use the MD4 algorithm rather than the default one.-m|-5Use the MD5 algorithm rather than the default one.-6Use the RMD160 algorithm rather than the default one.-oUse 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-roption. 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. The following options apply only when using the one of the message digest algorithms:-nPrint the hash and the filename in the normal sum output form, with the hash at the left and the filename following on the right.-pEcho input from standard input to standard output, and append the selected message digest.-sstringPrint the hash of the given stringstring.-tRun a built-in message digest time trial.-xRun 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 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 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: Thenbits to be evaluated are considered to be the coefficients of a mod 2 polynomial M(x) of degreen-1. Thesenbits 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. Thecksumandsumutilities exit 0 on success, and >0 if an error occurs.SEE ALSO

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

Thecksumutility is expected to conform to IEEE Std 1003.2-1992 (``POSIX.2'').HISTORY

Thecksumutility appeared in 4.4BSD. The functionality formd2,md4,sha1, andrmd160was added in NetBSD 1.6. NetBSD 2.1 October 18, 2002 NetBSD 2.1

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