A hash function used to get a
small integer number from a rather large information block. It results from a
calculation made on network
traffic information to detect errors made in the transmission or in the
duplication of files. CRCs are typically calculated before and after the
transmission or the duplication of files and then compared to confirm that they
are, indeed, alike. The most widely used CRC calculations are done in a manner
such that anticipated types of errors (such as transmission channel noise) are
usually detected.
It is important to note, however, that CRCs cannot be relied
upon to confirm the integrity of information (that is, that no alterations have
been made in the information) because through intentional modification, some crackers can cause changes in the data
that remain undetected by a CRC. However, cryptographic hash functions could be
used to verify data integrity. The important operation used to calculate a CRC
is binary division, with the remainder from the division operation determining
the CRC. In fact, CRC types are often identified by a polynomial—the number
used as the divisor, displayed in hexadecimal format. A frequently encountered
CRC type is that used by Ethernet,
PKZIP, WinZip, and PNG; namely, the polynomial 0x04 C11DB7 (a.k.a. CRC-32).
See Also: Crackers;
Ethernet; Network.
GNU_FDL. Cyclic Redundancy Check. [Online, 2004.] GNU_FDL Website.
http://www.free-definition.com/Cyclic-redundancy-check.html.
