CKSUM(1) BSD General Commands Manual CKSUM(1)NAME
cksum, md2, md4, md5, rmd160, sha1, sum — display file checksums and
block counts
SYNOPSIS
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]]
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 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 algo‐
rithms 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 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 ALSOopenssl(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 1003.1-2004
(“POSIX.1”).
HISTORY
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
