Research Of Decoding Homomorphic Encrypted FLAC Audio Without Decryption

Homomorphic Encryption(HE)allows processing ciphertext data,which is an effective solution of privacy-preserving data processing on the cloud.The multimedia data on the cloud is generally stored in a compressed state,thus it needs to be decompressed before processing.A scheme is proposed to enable the homomorphic encrypted FLAC(Free Lossless Audio Codec)decompression without decryption.It is a huge challenge to enable multimedia decompression in the HE domain.FLAC decoding relies heavily on dynamic controls that HE does not support due to unknown values of control variables after encryption.To address this issue,static controls can be regularized with dynamic controls in FLAC decoding by calculating an encrypted matching bit for each possible value of a control variable and producing candidate results as if it were a match.The summation of each possible value's candidate results multiplied by its matching bit is equivalent to selecting the results of the matched control value.The existing optimization of scheme is applied including multi-threading,batch bootstrapping,and Single-Instruction Multiple-Data(SIMD).Multi-ciphertext multiplication optimization is also proposed.SIMD means that multiple(e.g.256)plaintexts are packed and encrypted into a single ciphertext,and decoding one encrypted frame corresponds to decoding multiple plaintext frames.Experimental results verify the correctness of the scheme and show the effectiveness of the optimization.The scheme is also applicable to other audio compression standards based on similar coding technologies such as SILK,Apple Lossless,and MPEG-4 ALS.