CKSUM(1) | NetBSD General Commands Manual | CKSUM(1) |
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]] |
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 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 rmd160 and sha1 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:
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 |
md5 *.tgz > MD5
to generate a list of MD5 checksums in MD5, then use the following command to verify them:sha1 *.tgz > SHA1
If an error is found during checksum verification, an error message is printed, and the program returns an error code of 1.cat MD5 SHA1 | cksum -c
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.
The following options apply only when using the one of the message digest algorithms:
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:
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.
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.
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.January 2, 2009 | NetBSD 5.99 |