Practical applications of homomorphic encryption algorithms?

Question

It appears there there were interesting things going on in cryptography: the first homomorphic encryption scheme appeared recently (explanation, HT). Roughly sp

Answer 1

I don't know how expensive the f(x) + f(x) computation is going to be, but maybe it could be used as a way of implementing encrypted database.

You can store 1 million rows of some data encrypted as f(x_1), f(x_2), ... f(x_n). You could do

SELECT SUM(x)
FROM Foo
WHERE y = 'some value'

Which could be calculated by first doing SUM(f(x)) then decrypting it to SUM(x).