Secure Client- Server Delegated Computation: Difference between revisions

Delegated Computation is the task of assigning quantum computation to an untrusted device while maintaining privacy of the computation. Protocols under this functionality are commonly called ClientServer protocols. Delegated Quantum Computation (DQC) protocols involve partially/fully classical Client delegate a quantum computation task to a fully powerful quantum Server. All DQC protocols involve three main stages, Prepataion Stage, Computation Stage, Output Correction Stage. The roles of Client and Server in the different stages may differ according to the type of communication used. It can be performed via classical online/offline and quantum online/offline communication. It can be verifiable or non-verifiable. Hence, it is classified as follows, given that the client requires Server to perform Client quantum computation for her classical input/output.

It involves a partially quantum Client perform quantum and classical communication throughout the protocol. The Client and Server then exchange classical messages during the computation phase. Universal Blind Quantum Computation (UBQC) is a protocol falling under this category. In this protocol Client hides his input, output and computation from the Server using [[Supplementary Information#Measurement Based Quantum Computation|MBQC]] by sending hidden quantum states to the Server. Such UBQC protocols can be realised by a [[Measurement Only Universal Blind Quantum Computation|Measurement Only UBQC]] protocol where the client measures some known quantum state prepared by server in a rotated basis to generate input states. Same as UBQC, VUBQC can also be realised by [[Measurement Only Verifiable Universal Blind Quantum Computation|Measurement Only VUBQC]] protocols. Version for quantum input/output is also available in the descriptions.

It involves a partially classical Client exchanging performing both classical and quantum communication with the Server during the preparation stage and output correction. There is no communication between the two parties during computation stage. Client hides her input states with the help of some classical encryption using [[Supplementary Information#Homomorphic Encryption|HE]] and some quantum gadgets (using [[Supplementary Information#entanglement|entanglement]]). Server performs computation on the encrypted state using these quantum gadgets. Later Client decrypts the outcome sent by Server to get the correct result. Protocols falling under this category are Quantum Fully Homomorphic Encryption (QFHE) Just like UBQC, QFHE protocols can also be realised by a [[Prepare and Send Quantum Fully Homomorphic Encryption|Prepare and Send QFHE]] protocol where client prepares and sends the input states to the Server. If the task performed by the Server can be verified by the Client, the protocol is called, Verifiable Quantum Fully Homomorphic Encryption [[Verifiable Quantum Fully Homomorphic Encryption (VQFHE). Same as QFHE, VQFHE can be realised by [[Prepare and Send Verifiable Quantum Fully Homomorphic Encryption|Prepare and Send VQFHE]]. For both QFHE and VQFHE, Measurement Only protocols are an open case. Version for quantum input/output is also available in the descriptions.

It involves a fully classical Client exchanging classical messages with the server only during the preparation and output correction phase. There is no communication during computation phase. It uses only classical [Supplementary Information#Homomorphic Encryption|HE] and no quantum gadgets to realize a quantum functionality. Protocols falling under this category are Classical Fully Homomorphic Encryption [[Classical Fully Homomorphic Encryption for Quantum Circuits|(FHE) for Quantum Circuits]]. A verification of FHE for Quantum Circuits protocol is still an open question. Version for quantum input/output is also available but that would require quantum offline communication. It is different from QFHE as it would use a completely classical HE and hence, the Client would not be required to not generate entanglement, which is difficult but be simple enough to only prepare and send quantum states.