NAME
cksum,
md2,
md4,
md5,
rmd160,
sha1,
sum —
display file checksums and
block counts
SYNOPSIS
cksum |
[-n]
[-a algorithm
[-pqtx]
[-s
string]]
[-o
1|2]
[file ... |
-c [-w]
[sumfile]] |
sum |
[-n]
[-a algorithm
[-pqtx]
[-s
string]]
[-o
1|2]
[file ... |
-c [-w]
[sumfile]] |
md2 |
[-npqtx]
[-s
string]
[file ... |
-c [-w]
[sumfile]] |
md4 |
[-npqtx]
[-s
string]
[file ... |
-c [-w]
[sumfile]] |
md5 |
[-npqtx]
[-s
string]
[file ... |
-c [-w]
[sumfile]] |
rmd160 |
[-npqtx]
[-s
string]
[file ... |
-c [-w]
[sumfile]] |
sha1 |
[-npqtx]
[-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 |
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
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 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 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.
-
-
- -q
- Quiet mode — only the checksum is printed out.
Overrides the -n option.
-
-
- -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 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 networking standard
ISO 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
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 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 1003.1-2004 (“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.
Quiet mode (
-q) was added in
NetBSD
7.0.