Posts by Simon Whitehouse

Modern 'primitive' could ease the pain of encrypting massive amounts of data

Symetric and assymmetric encryption systems

"Functional encryption is designed to solve the hassle tied to traditional public-key encryption resulting from distributing and managing thousands or millions of private keys authorized people need to decrypt protected data. If 1,000 people in an organization need to securely share their public key with their co-workers, that requires close to one million separate exchanges."

You seem to be getting confused between symmetric and assymmetric encryptions. In a symmetric system you have a seperate secret key that you exchange with everybody. Total number of keys needed is n(n+1)/2 which does get very near to a million for 1000 employees.

In an assymmetric system you have one public key that is available to everybody. There is no need to secure your public key, as it's a public key: there is a clue in the name after all. In an assymmetric system you only need n keys.

Peruvian 'meteorite' strike provokes noxious gas attack

800 miles south of Lima?

"According to the BBC, the impact occurred on Saturday night near Carancas in the Puno region, around 800 miles (1,300km) south of Lima."

In which case they are missing the bigger story, as Carancas, which used to be in the Andes, near the border with Bolivia, now appears to be in the Pacific Ocean.

http://maps.google.co.uk/maps?oe=UTF-8&hl=en&tab=wl&q=peru

Exams, contracts, and nuclear research: stupid, stupid, stupid

Mineshaft maths

Ok, 38 no calc.

Circumference = pi.d = 22/7*7/10m = 2.2 m

So, with 10 rpm we need 1 minute to descend or ascend the shaft. We need 3 journeys to evacuate all of the people in the mine and each of these will take 2 minutes 20 seconds to complete. Total time taken is therefore 7 minutes.