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We perform checksums of some data in sql server as follows:
declare @cs int;
select
@cs = CHECKSUM_AGG(CHECKSUM(someid, position))
from
SomeTable
where
userid = @userId
group by
userid;
This data is then shared with clients. We'd like to be able to repeat the checksum at the client end... however there doesn't seem to be any info about how the checksums in the functions above are calculated. Can anyone enlighten me?
729
The checksum algorithm is really a special kind of hash function. A hash function is a function, or process, that can be used to map data of arbitrary size to data of a fixed size. The types of hashes used for data integrity are distinguished by the presence or absence of keys and cryptographic properties.
The SHA family of algorithms is published by the National Institute of Standards and Technology. One algorithm, SHA-1, produces a 160-bit checksum and is the best-performing checksum, followed by the 256-bit and 512-bit versions.
CHECKSUM computes a hash value, called the checksum, over its argument list. Use this hash value to build hash indexes. A hash index will result if the CHECKSUM function has column arguments, and an index is built over the computed CHECKSUM value. This can be used for equality searches over the columns.
A cryptographic hash, or checksum, is a digital fingerprint of a piece of data (e.g., a block of text) which can be used to check that you have an unaltered copy of that data. Emacs supports several common cryptographic hash algorithms: MD5, SHA-1, SHA-2, SHA-224, SHA-256, SHA-384 and SHA-512.
On SQL Server Forum, at this page, it's stated:
The built-in CHECKSUM function in SQL Server is built on a series of 4 bit left rotational xor operations. See this post for more explanation.
138
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