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On the definition of 'Angry Mob Cryptanalysis'
by Decius at 9:52 am EDT, Sep 26, 2009

In a recent blog post, which you cannot read because it was censored by a DMCA takedown notice from Texas Instruments, I used the term "Angry Mob Cryptanalysis" to refer to a situation in which a distributed key cracking effort is targeted at a public key that is widely known and widely resented. This term has an origin in the annals of computer security research and my use of it might be misunderstood so I felt that I should elaborate.

Matt Blaze originally coined the term "Angry Mob Cryptanalysis" in a paper he wrote back in 1996 about government key escrow. The term and its origin are burned into my brain because I recall being excited at the prospect - a democratic check upon communications security!

In Blaze's paper a person would broadly distribute shards of his private key. If that person was later accused of a crime the police might issue a public call for shards. If a large number of people were sympathetic to the call they might reveal their shards, allowing the police to proceed with monitoring that person. Its sort of like replacing judicial warrants with a grand jury system, enforced with hard mathematical constraints that cannot be subverted. If the police want to intrude upon someone's privacy they'd have to convince a large enough group of people in the community in order to do so. A very interesting and brilliant idea with numerous variations.

But if you think about it, every key faces a threat to its security from the general public in a world where distributed key cracking efforts can be organized, regardless of whether the creator of that key intentionally escrowed it with the public in the first place. I think the term "Angry Mob Cryptanalysis" is fitting in any situation where there is a public effort to crack a key. Its a risk that designers of crypto systems need to consider - how widely distributed is your public key, what is the key strength, and how much public resentment might exist about it? If the key is weak enough and the resentment high enough, you might fall victim to a public cracking effort.

A perfect example of a place where this might be useful is the context of a computer worm like Conficker. Conficker.B currently controls about 5 million hosts on the Internet, and the security experts who monitor it are concerned that those infected nodes represent a collective threat to Internet security. For example, they could be used to launch denial of service attacks if the Conficker bot master was able to update them. Fortunately, the bot master is blocked through a daily effort by members of the Conficker Working Group to contro... [ Read More (0.2k in body) ]

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