Abstract
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.
Highlights
With the growth of video services such as video streaming, video conferencing, and video surveillance, the total amount of video content, as well as the types of content available, has been increasing and diversifying
The encrypted bitstream is converted into a restored bitstream by restoring the first bytes that are scrambled after the start code using the restored encryption lookup table (ELUT)
The first bytes of the network abstraction layer (NAL) unit headers included in the original bitstream of Type 11 are ‘0×40’, ‘0×42’, ‘0×44’, ‘0×50’, ‘0×00’, ‘0×02’, and ‘0×26’, which correspond to the NAL units of Video Parameter Set (VPS), Sequence Parameter Set (SPS), Picture Parameter Set (PPS), SUFFIX_SEI, Trailing Non-reference (TRAIL_N), Trailing Reference (TRAIL_R), and IDR_W_RADL, respectively
Summary
With the growth of video services such as video streaming, video conferencing, and video surveillance, the total amount of video content, as well as the types of content available, has been increasing and diversifying. The NAL unit that is expected to be an I picture is a case where an NAL unit of PPS or PREFIX_SEI previously exists, and the RBSP size of the NAL unit is different from the payloadSize obtained by parsing the NAL unit according to Table VIII. In this case, the nal_unit_type of the NAL unit is replaced with IDR_W_RADL.
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