Cryptography's window of usefulness (request for link)

[lebing]

In another forum I belong to, someone said (claiming to have a background in cryptography) that the usefulness of such a system was limited to around 200 years because after that point the computers will be too fast and therefore cryptography as a method of security will be outdated.

I remember reading somewhere that it would take more computing power than energy was in the sun (or something insane like this) in order to hack a private key. Does anyone have the link to what I am referring to?

Thanks

[laanwj]

Well, we're still limited by physics, even in 200 years. So I suppose that can give a pretty certain upper bound.

As the key space is 2^256 ~ 10^77 for Bitcoin private keys (2^160 ~ 10^48) if you count colliding addresses after hashing the pubkey), I don't think any realistic attacks will come from the "throw more computing power at it" angle. However it's always possible that the schemes will be mathematically broken.

BTW a bit of googling will reveal many similar discussions.

[Remember remember the 5th of November]

When quantum computers break normal cryptography, it will be replaced with quantum cryptography, no?

[Come-from-Beyond]

When quantum computers break normal cryptography, it will be replaced with quantum cryptography, no?

No need to replace everything. Conventional algos (for example, http://en.wikipedia.org/wiki/Lamport_signature) will work even after the rise of quantum computing.

[lebing]

When quantum computers break normal cryptography, it will be replaced with quantum cryptography, no?

No need to replace everything. Conventional algos (for example, http://en.wikipedia.org/wiki/Lamport_signature) will work even after the rise of quantum computing.

Why is that exactly? I dont see any reference to it in the wiki.

[Come-from-Beyond]

When quantum computers break normal cryptography, it will be replaced with quantum cryptography, no?

No need to replace everything. Conventional algos (for example, http://en.wikipedia.org/wiki/Lamport_signature) will work even after the rise of quantum computing.

Why is that exactly? I dont see any reference to it in the wiki.

Sorry, I didn't check if Wiki mentions about quantum resistant feature of Lamport signature. Here a link to other paper - http://www.nist.gov/customcf/get_pdf.cfm?pub_id=901595, search for "Lamport".