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.
9. The method of claim 5 , wherein the doubly-encrypted frequency for each of the n-grams in each set of n-grams is generated with a key for homomorphic multiplication which is not provided to the server.