1. A method of privately searching for keyword criteria in an electronic document, the method comprising: a) initializing an encryption variable to a value being an encryption of an identity element under a homomorphic and probabilistic Chosen Plaintext Attack-secure (CPA-secure) encryption scheme; b) receiving an electronic document comprising a plurality of document words; c) looking up each of the plurality of document words in a dictionary of known words, each of the known words being either a keyword or an irrelevant word, each of the irrelevant words having associated therewith a correspondingly unique cipher-text having a value that is an encryption of the identity element under the encryption scheme, and each of the keywords having associated therewith a correspondingly unique cipher-text having a value that is an encryption of a non-identity element under the encryption scheme; d) for each of the plurality of document words found during the lookup step, performing an operation associated with the encryption scheme on a first operand and a second operand, the first operand being the cipher-text corresponding to the found document word and the second operand being the encryption variable, each time changing the value of the encryption variable to be the result of the operation, the encryption variable ending with a final value; e) encrypting the electronic document using the encryption variable; f) writing the encrypted electronic document to a first slot in a buffer comprising a plurality of slots, each of the plurality of slots having been initialized to contain an encryption of the identity element prior to the encrypted electronic document being written to the first slot.
5. The method of claim 1 , wherein if a decrypted value of the electronic document is zero then the electronic document is not a matching document, and if the decrypted value of the electronic document is not zero and is not a collision of two or more electronic documents, then the decrypted value of the electronic document is the electronic document.