Evil bit
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The evil bit is a fictional IP packet header field proposed in RFC 3514, a humorous April 1st RFC from 2003 authored by Steve Bellovin. The RFC recommended that the last remaining unused bit in the IPv4 packet header be used to indicate whether a packet had been sent with malicious intent, thus making computer security engineering an easy problem.
The joke is that:
- it is impossible to come up with a rigorous yes-or-no definition of what constitutes an "evil" packet, which is a necessarily subjective human value judgement
- even if such a definition existed, a host on the other side of an untrusted network could not be trusted to set the bit correctly
The evil bit has become a synonym for all attempts to seek simple technical solutions for difficult human social problems, in particular efforts to implement Internet censorship using simple technical solutions.
The evil bit also became a noteworthy in-joke in Slashdot. News about the publication of this RFC was posted in Slashdot dozens of times, reworded each time, among other April Fools stories, poking humour at the common criticism of Slashdot often posting duplicate stories.
As a joke, FreeBSD implemented this on the same day but removed the changes on the following day.
This RFC has also been quoted in the otherwise completely serious RFC 3675, ".sex Considered Dangerous", which may have caused the proponents of .xxx to wonder whether the Internet Engineering Task Force (IETF) was commenting on their application for a top-level domain (TLD) - the document was not related to their application.
