In the world of digital currencies, security and privacy represent a serious challenge. Since the launch of bitcoin, many hack attacks have occurred, leading to the loss of millions of dollars. Furthermore, when bitcoins are stolen, not only the direct victim is affected, but also the whole bitcoin market is undermined by considerable fluctuations in bitcoin’s price. Every node across bitcoin’s network stores a copy of the transaction records, referred to as the blockchain. Every set of transactions submitted to the network during a specific time period is grouped into a block, and blocks are chained sequentially, forming the blockchain.
The public ledger that records all data of transactions is publically available to everyone, so an adversary can obtain all transaction data, undermining the privacy of users. Via bitcoin transaction analysis, an attacker can retrieve all transactions associated with any address and can also obtain the relationships between different addresses. To protect the privacy of bitcoin users, several privacy protection approaches have been proposed. The main concept is to conceal some of the information broadcast to the public ledger without undermining the normal operations of the Bitcoin network, and to render data analysis more difficult to perform successfully. High Efficiency Video Coding (HEVC) represents a novel and advanced approach for compression of videos with advanced compression efficiency. HEVC can be used in network transmission. A recently published research study proposed the use of HEVC video to conceal transaction information in order to boost the security and privacy of bitcoin transactions.
Hiding bitcoin transaction data in HEVC videos:
Intra-frame distortion drift represents a major obstacle for hiding data in streams of HEVC videos. Since the beginning of the period of H.264/AVC, developers have suggested methods for data hiding algorithms without intra-frame distortion drift. In 2009, researchers deployed the paired coefficients of a special 4 x 4 DCT block to embed data in order to compensate for intra-frame distortion. In 2010, a group of researchers worked on improving the algorithm via employment of the paired coefficients in addition to the directions of intra-frame prediction in order to mitigate the problem of distortion drift. Nevertheless, algorithms developed on the basis of H.264/AVC cannot be implemented with HEVC, namely for HEVC’s 4 x 4 luminance blocks, where discrete sine transform (DST) is utilized alternatively to DCT. To mitigate the problem of coefficient distortion drift in HEVC, a group of researchers in 2013, introduced a set of three-tuple, which had an effect similar to the paired coefficients used in previously proposed algorithms.
The newly proposed method involves the use of HEVC for hiding bitcoin transaction information. Developers of the proposed method formulated a coefficient compensation rule, in addition to three-tuple-groups with coefficients that meet this rule. The formulated coefficient compensation rule can be applied to 4 x 4 luminance DST blocks in order to embed bitcoin transaction information to mitigate intra-frame distortion. The data embedding strategy is implemented to these three-tuple groups for the purpose of improving the visual quality of the used video.
Testing the proposed method:
The proposed approach for hiding bitcoin transactions was deployed in version HM16.0 of the HEVC reference software. During the experiments, the researchers used “Basketball” (416 * 240), “Keiba” (416 * 240), and “Akiyo” (176 * 144) as test videos. GOP size is adjusted to 1, and QP values are adjusted to 16, 24, 32, and 40. Due to the fact that 4 bits of bitcoin transaction data can be embedded in a single 4 x 4 luminance DST block, the using probability of (1, -1, 1) mode is set to 0.75, and the using probability of (1, -2, 8) mode is set to 0.25.
With increasing the value of QP, the qualities of the embedded image and decoded image are reduced. Single usage of three-tuple (1, -1, 1) can markedly alter multiple fixed pixels in the 4 x 4 luminance DST blocks, which can produce significant hot pixels provided that the value of QP is big.
As such, experiments showed that coefficient compensation rule, in addition to hybrid three-tuple, can efficiently hide bitcoin transaction information, while preventing intra-frame distortion drift. Via cross utilization of multiple three-tuple, this method can yield better visual results when compared to usage of single three-tuple. Experiments conducted by developers of the method have proven its superiority and feasibility in hiding bitcoin transaction information.