Distributed Checksum Clearinghouse (also referred to as DCC) is a method of

spam Spam may refer to: * Spam (food), a canned pork meat product * Spamming, unsolicited or undesired electronic messages ** Email spam, unsolicited, undesired, or illegal email messages ** Messaging spam, spam targeting users of instant messaging ( ...

email detection. The basic logic in DCC is that most spam mails are sent to many recipients. The same message body appearing many times is therefore bulk email. DCC identifies bulk email by calculating a

fuzzy checksum A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify dat ...

on it and sending that to a DCC server. The server responds with the number of times it has received that checksum. An individual email will create a score of 1 each time it is processed. Bulk mail can be identified because the response number is high. The content is not examined. DCC works over the UDP protocol and uses little

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

. DCC is resistant to

hashbusters A hash buster is a program which randomly adds characters to data in order to change the data's hash sum. This is typically used to add words to spam e-mails, to bypass hash filters. As the e-mail's hash sum is different from the sum of e-mails p ...

because "the main DCC checksums are fuzzy and ignore aspects of messages. The

s are changed as spam evolves"Distributed Checksum Clearinghouses official website
/ref> DCC is likely to identify mailing lists as bulk email unless they are white listed. Likewise, repeatedly sending the same email to a server increases its number in the server, and, therefore, the likelihood of it being treated as spam by others.

History

According to the official DCC website:

The DCC is based on an idea of
Paul Vixie Paul Vixie is an American computer scientist whose technical contributions include Domain Name System (DNS) protocol design and procedure, mechanisms to achieve operational robustness of DNS implementations, and significant contributions to open ...
and on fuzzy body matching to reject spam on a corporate firewall operated by
Vernon Schryver Vernon may refer to: Places Australia *Vernon County, New South Wales Canada *Vernon, British Columbia, a city *Vernon, Ontario France * Vernon, Ardèche *Vernon, Eure United States * Vernon, Alabama * Vernon, Arizona * Vernon, California ...
starting in 1997. The DCC was designed and written at Rhyolite Software starting in 2000. It has been used in production since the winter of 2000/2001.

References

External links

* {{Spamming Spam filtering