Effectiveness of Crypto-Transcoding for H.264/AVC and HEVC Video Bit-streams

TL;DR

This paper evaluates a joint crypto-transcoding scheme for H.264/AVC and HEVC video streams that allows secure bitrate reduction without full decryption, enhancing efficiency and privacy in adaptive streaming networks.

Contribution

It introduces a novel selective encryption-based crypto-transcoding method that enables secure, efficient bitrate adjustment of video streams without exposing decryption keys at intermediate points.

Findings

AES outperforms XOR encryption for SE in terms of visual distortion.

Bitrate reduction is effective with minimal computational overhead.

Content and codec type influence the distortion levels after transrating.

Abstract

To avoid delays arising from a need to decrypt a video prior to transcoding and then re-encrypt it afterwards, this paper assesses a selective encryption (SE) content protection scheme. The scheme is suited to both recent standardized codecs, namely H.264/Advanced Video Coding (AVC) and High Efficiency Video Coding (HEVC). Specifically, the paper outlines a joint crypto-transcoding scheme for secure transrating of a video bitstream. That is to say it generates new video bitrates, possibly as part of an HTTP Adaptive Streaming (HAS) content delivery network. The scheme will reduce the bitrate to one or more lower desired bit-rate without consuming time in the encryption/decryption process, which would be the case when full encryption is used. In addition, the decryption key no longer needs to be exposed at intermediate middleboxes, including when transrating is performed in a cloud datacenter. The effectiveness of the scheme is variously evaluated: by examination of the SE generated visual distortion; by the extent of computational and bitrate overheads; and by choice of cipher when encrypting the selected elements within the bitstream. Results indicate that there remains: a content; quantization level (after transrating of an encrypted video); and codec-type dependency to any distortion introduced. A further recommendation is that the Advanced Encryption Standard (AES) is preferred for SE to lightweight XOR encryption, despite it being taken up elsewhere as a real-time encryption method.