Challenge/Response is a DDoS tool hidden in an
anti-spam system. Consider this scenario:
mallory@spamcompany.com sends out a million spams in which he puts
alice@wonderland.com in the "From" field. Those running a
challenge/Response tool automatically send out a challenge to
alice@wonderland.com on receipt of this spam. If there were 10,000
people running a challenge/response tool, Alice will receive 10,000
challenges! If all of these had 10k+ graphics in them (as they usually
do), Alice would receive 100Mb of mail in a matter of few minutes. This
might disrupt Alice's mail servers, cause her to lose legitimate mail,
waste several hours of her time, and quite likely force Alice (or her
mail administrator) to drop all future challenges generated by
Challenge/Response softwares involved in the incident; even those sent on receipt of
emails that were written by Alice.
(See my complete response to PC Magazine reviewers
on whitelisting and Challenge/Response
here)
Postulating a big bang to explain red shift has always seemed particularly
unimaginative to me. But that's besides the point. I still believe that
theorizing about the beginning of universe is pointless and will remain
pointless in times to come (pun most definitely intended), because we
observe a local region, and while our definition of local will change as
we learn more, we will still only see a local region, dammit!
Properties of local regions differ tremendously (from the real picture) in
the Universe, as all the classical physicists found out, much to their
dismay, in the early 20th century. I am pretty sure, more advanced
civilizations around the universe have written it off as the NP-hard
problem of all times.
Some of you point out that Razor's use of SHA-1
signatures can be defeated by introducing
randomness in the message. This is true;
SHA-1 will eventually be phased out and replaced
by a
fuzzy hashing mechanism like nilsimsa
in future. [http://lexx.shinn.net/cmeclax/nilsimsa.html]
[http://www.geocrawler.com/archives/3/2539/2001/7/ 0/6173567/]
The protocol is structured to aid change of
hashing algorithms seamlessly, without breaking
the existing system.
Regarding the possibility of poisoning the database, we are working on a reputation system
that will assign credit to honest reporters.
Once we have a critical mass of users, it would
be hard for dishonest reporters to even join
the reporting network, much less be able to
mount a DOS attack.
Some of these issues have been discussed on the
razor-users mailing list. The list archives
are located at
[http://www.geocrawler.com/archives/3/2539/2001/]
best,
vipul.
Slashdot Mirror
Challenge/Response is a DDoS tool hidden in an anti-spam system. Consider this scenario: mallory@spamcompany.com sends out a million spams in which he puts alice@wonderland.com in the "From" field. Those running a challenge/Response tool automatically send out a challenge to alice@wonderland.com on receipt of this spam. If there were 10,000 people running a challenge/response tool, Alice will receive 10,000 challenges! If all of these had 10k+ graphics in them (as they usually do), Alice would receive 100Mb of mail in a matter of few minutes. This might disrupt Alice's mail servers, cause her to lose legitimate mail, waste several hours of her time, and quite likely force Alice (or her mail administrator) to drop all future challenges generated by Challenge/Response softwares involved in the incident; even those sent on receipt of emails that were written by Alice. (See my complete response to PC Magazine reviewers on whitelisting and Challenge/Response here)
Properties of local regions differ tremendously (from the real picture) in the Universe, as all the classical physicists found out, much to their dismay, in the early 20th century. I am pretty sure, more advanced civilizations around the universe have written it off as the NP-hard problem of all times.
Existence exists; deal with it. :-)
Some of you point out that Razor's use of SHA-1 signatures can be defeated by introducing randomness in the message. This is true; SHA-1 will eventually be phased out and replaced by a fuzzy hashing mechanism like nilsimsa in future. [http://lexx.shinn.net/cmeclax/nilsimsa.html] [http://www.geocrawler.com/archives/3/2539/2001/7/ 0/6173567/]
The protocol is structured to aid change of
hashing algorithms seamlessly, without breaking
the existing system.
Regarding the possibility of poisoning the database, we are working on a reputation system
that will assign credit to honest reporters.
Once we have a critical mass of users, it would
be hard for dishonest reporters to even join
the reporting network, much less be able to
mount a DOS attack.
Some of these issues have been discussed on the
razor-users mailing list. The list archives
are located at
[http://www.geocrawler.com/archives/3/2539/2001/]
best,
vipul.