5. The method of claim 2 , wherein the server receives doubly-encrypted resources from the client generated from the encrypted resources provided to the client, the doubly-encrypted resources including doubly-encrypted frequencies generated by further encrypting the encrypted frequencies of n-grams in the encrypted resources with a key for homomorphic multiplication.
5. The method of claim 2 , wherein the server receives doubly-encrypted resources from the client generated from the encrypted resources provided to the client, the doubly-encrypted resources including doubly-encrypted frequencies generated by further encrypting the encrypted frequencies of n-grams in the encrypted resources with a key for homomorphic multiplication. 8. The method of claim 5 , wherein the doubly-encrypted frequencies are encrypted with a homomorphic additive encryption scheme selected from Paillier and Benaloh encryption and with ElGamal homomorphic multiplicative encryption.