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So, browsing through YouTube, I stumbled on this video interview of John Draper (Captain Crunch), one of the first "hackers". He talks for about 3 minutes (until 27:48) about his home rolled encryption method that will use 1 billion bit keys that randomly change every 5 seconds.

My first thought is, is this guy full of crap? But, more specifically, if we have the capability to use 1 billion bit encryption (he claims an overhead of only 250kb to transport keys), why don't we see keys much longer than 4096? Other than the fact that it seems like an insane overkill.

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How about 9 trillion bit cryptography? –  Matt Nordhoff 5 hours ago
Ridiculous key lengths are one of the primary indicators of bullshit in the crypto world. "Proprietary" schemes are another. Winning a game of buzzword bingo within the first sentence seals the deal. Physical limits on computation mean there's no need for such excessively long keys. Even though public-key crypto has inherently easier attacks than symmetric crypto, there's no point in going that big. Bremermann's limit means that brute forcing a 512-bit symmetric key with a computer the mass of the earth would take 10^72 years. ECC needs keys >=2x that of symmetric to get the same security. –  SAI Peregrinus 4 hours ago

2 Answers 2

Examining his claims about "Thundercloud":

  • You can use it with "any existing software, operating system, or device" (a massive amount of effort---by whom?)
  • Has its "own cryptographic language that is completely independent of any existing security technology" (this is a negative thing: abandoning the entire knowledge base of cryptography is incredibly stupid)
  • Its strength is "built within [its] proprietary design of the public and private cryptographic keys" (proprietary design is not a strength)
  • Those keys are 1 billion bits (125 megabytes!!!)
  • Those keys are "rotated randomly every 5 seconds" (a generation rate of 200 megabits per second)
  • Those keys are "controlled entirely by the user" (how they can generate 200 megabits per second is beyond me)
  • "No information is ever stored... besides of our standard encryption keys in excess of a terabyte data block" (???)
  • However, the above is what makes their technology so exciting---since it's transferred in the space of 200 kilobytes! (what?)
  • Will conform to any existing method of data storage or communication without any overhead
  • "Most security keys range from 128-bit to 4096-bit" (I guess the range includes both symmetric and asymmetric encryption!)
  • Since "most" security keys are so small, "cracking security keys in this size is fairly easy with enough computational power" (of course this is true---by definition, "enough" computational power will break computational security; that's kind of the point)
  • Current cryptographic technology is no longer safe: even RSA crypto was discovered to have "back doors" (yes, recently a blog post circulated showing that RSA can be backdoored if you let someone else control key generation, but that is practically a non-issue)
  • The system is designed from the ground-up to be impossible to breach
  • Every supercomputer in the world in tandem can't break it! (Neither can they break ChaCha20 with its 256-bit key, though, either......)
  • Adding tracking elements to Thundercloud is "technically impossible"

Needless to say, I am very skeptical. He certainly uses many technical terms, but there's very little substance. Sporting massive key sizes are a telltale sign of bullshit.

Answering your question directly: 128-bit encryption is generally considered very sufficient. Maybe it is not very sufficient: then you can pick 256-bit, whose breaking by exhaustive search is "totally out of the reach of mankind".

If exhaustive search of a 256-bit keyspace is totally out of the reach of mankind, why should you use 1 billion bit keys? Even if you built a system that could, is the massive overhead of trying to use a 1-billion-bit key really worth it? I wouldn't say so: not when 256-bit keys suffice.

Some schemes can be broken much faster than by doing an exhaustive search. For example, to get "256 bits of security," you need 15360 bits for RSA, so there's an example of needing a really, really, really large key to attain a certain security level. (Also, notice that I'm saying 15Kbits is really, really, really large. Imagine how I must feel about a gigabit!)

(Almost?) all practical cryptosystems might be broken in the near future, so we can't say that 256-bit encryption with, say, ChaCha20 gives you ironclad, unstoppable security. At the same time, though, if we somehow extended ChaCha to use a gigabit key, there's no guarantee that a new attack would necessarily be thwarted by such a large key, either. So, I don't view excessively large keys as great "insurance" against future cryptanalytic attacks.

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Yes, he is full of crap.

If you go to KeyLength, you can compare key lengths for different cryptosystems and see how long they're expected to be secure for.

It's just a performance vs security tradeoff that implementers make. Most people don't see the point in schlepping around megabytes of key material for cryptosystems that are expected to be secure against quantum attacks and more advanced cryptanalysis, so they certainly don't see the point in schlepping around hundreds of megabytes of key material for a cryptosystem that we expect to see die in our lifetimes.

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