Cryptanalysis of Start Code-Based Encryption Method for HEVC

We propose a cryptanalysis for MPEG high efficiency video coding bitstream encryption based on the start code. Today, most digital video data are transmitted over an open Internet network in an encrypted state for security and privacy. In general, video services must guarantee real-time communications; therefore, it is necessary to reduce the computational complexity required to encrypt video data. Consequently, many selective encryption algorithms that selectively encrypt a highly sensitive part of the entire video data have been studied. Recently, we proposed a selective encryption algorithm based on the start code for high efficiency video coding, which dramatically reduces the computational complexity of encryption. In this paper, we studied the cryptanalysis of the encryption algorithm based on the start code and found a security vulnerability for a ciphertext-only attack. The proposed method presents a method to restore the encrypted first byte of the network abstraction layer unit header by analyzing the unencrypted high efficiency video coding bitstream. The first byte of the network abstraction layer unit header can be restored using the unencrypted parts, such as the order, syntax element, and length of the network abstraction layer unit. The experimental results demonstrated the security vulnerability by breaking the start code based encryption algorithm that is difficult to recover using the brute-force attack with only one to six recovery attempts using the proposed ciphertext-only attack.