
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 12] [file ...  c [w] [sumfile]]
sum [n] [a algorithm [ptx] [s string]] [o 12] [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 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
written.
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 RIPEMD160
SHA1 160 SHA1, per FIPS PUB 1801
SHA256 256 SHA2
SHA384 384 SHA2
SHA512 512 SHA2
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 16bit 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 32bit 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 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 builtin message digest time trial.
x Run a builtin 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 SHA1 algorithm and the
RIPEMD160 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 network
ing standard ISO/IEC 88023:1989. 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 pro
cedure:
The n bits to be evaluated are considered to be the coefficients of a mod 2 polynomial
M(x) of degree n1. These n bits are the bits from the file, with the most signifi
cant 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 nec
essary) to achieve an integral number of octets, followed by one or more octets repre
senting 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 32bit 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 pseudocode in the following ACM arti
cle.
Dilip V. Sarwate, "Computation of Cyclic Redundancy Checks Via Table Lookup", Communications
of the ACM, August 1988.
R. Rivest, The MD2 MessageDigest Algorithm, RFC 1319.
R. Rivest, The MD4 MessageDigest Algorithm, RFC 1186 and RFC 1320.
R. Rivest, The MD5 MessageDigest Algorithm, RFC 1321.
U.S. DOC/NIST, Secure Hash Standard, FIPS PUB 1801.
STANDARDS
The cksum utility is expected to conform to IEEE Std 1003.12004 (``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 SHA2 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 
