A retrieval algorithm for encrypted speech based on convolutional neural network and deep hashing

In this paper, we propose a retrieval algorithm for encrypted speech based on the convolution neural network (CNN) and deep hashing. It is used to overcome the feature extraction defects of the existing content-based encrypted speech retrieval methods, and solve the problem of low retrieval accuracy caused by high dimensional and temporality of audio data. Firstly, the study encrypts the original speech by the three-dimensional chaotic encryption algorithm and uploads it to the encryption speech library in the cloud. Since CNN can well capture the basic semantic structure features of speech data, we use CNN as a feature extractor to extract deep features from Log-Mel spectrogram/MFCC. The batch normalization algorithm is introduced in the training process, which improves the speed of network fitting, reduces the training time, and improves the retrieval efficiency of the system. Secondly, the deep features extracted from CNN are combined with the hash function to construct the system hashing index table. Finally, the retrieval is implemented by the normalized Hamming distance algorithm. The experimental results show that the proposed algorithm has better discrimination, robustness to amplitude change compared with the existing methods. Meanwhile, the proposed algorithm has a high recall, precision, and retrieval efficiency after various content preserving operations.