Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Particular communication authentication technique
Reexamination Certificate
1999-12-02
2004-04-20
Barrón, Gilberto (Department: 2132)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Particular communication authentication technique
C382S100000, C380S210000, C380S201000, C380S202000, C380S203000
Reexamination Certificate
active
06725372
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application relates to the field of digital multimedia and more particularly to the field of watermarking digital multimedia content.
2. Description of Related Art
Enforcing ownership rights in digital content may be difficult due to the relative ease with which the content can be reproduced and distributed. Secure communication provides one form of protection. Encryption may prevent outsiders from viewing a video sequence, but once the video stream has been decrypted, there is no protection against manipulation and redistribution of the stream. Further, where widespread distribution of multimedia content is desired, key-management for a typical public key encryption scheme becomes cumbersome. In addition, encryption may require error-free communications, which may not be available in all networks, particularly in a wireless network. Thus, there is an interest in supplemental security methods for multimedia content.
Another form of protection is provided by a message authentication code (“MAC”) that is attached to digital content. For example, origination information may appear within a message field appended to digital content. However, this type of add-on authentication is easily identified and removed. A more resilient MAC system is provided by digital watermarking.
Digital watermarking is a technique for hiding an identification of origin in a digital media stream. A digital watermark is actually embedded in the media stream in a way that inhibits removal without destroying the underlying content. The watermark may also be folded into the original data in a manner that is imperceptible to the listener/viewer. When such watermarked digital content is distributed on-line, or recorded on a disk, the origination data travels with it, and allows the originator to demonstrate the source of the content. Digital watermarking also identifies tampering, since any manipulation of a sequence will result in an invalid watermark.
One technique for encoding multimedia content is detailed in the well-known Moving Picture Experts Group (“MPEG”) 2 standard. MPEG-2 is based upon a process of breaking an image frame up into fixed-size blocks, converting the blocks to luminance/chrominance data, transforming the blocks using a discrete cosine transform (“DCT”), and quantizing the transformed data. The resulting “I frame” includes Y blocks for luminance (four in MPEG-2's main level at main profile) and C blocks for chrominance (two in the main level at main profile) for each block of the frame. Each block contains a matrix of coefficients calculated from a Y or C block using the DCT. This step compresses data by removing so-called spatial redundancies, which may loosely be considered as similar-looking content in different areas of a block. Variable-length coding is then used to compress long runs of zeroes that are typical of high spatial-frequency coefficients. Still further compression is achieved by coding consecutive frames into “P frames” (predictive) and “B frames” (bi-directional), which only include information describing changes relative to neighboring chronological frames.
One known technique for watermarking such an MPEG-2 video stream is to use the DC coefficients of the Y blocks in each I frame of the MPEG-2 stream to effectively form a parity bit. According to this technique, the median DC coefficient of each sequential group of three Y blocks is forced to be always even or odd, depending on the watermark bit being encoded. This technique has a minimal impact on image quality and is relatively simple to implement. However, as a significant disadvantage thereof, this technique is not particularly robust. In many instances, only one out of every fifteen frames of an MPEG-2 video stream is an I frame, only two out of three blocks in an I frame is a Y block, and only one out of every three Y blocks is coded for watermarking. In those instances, very few bits of the overall bit stream are actually used for a watermark. Thus a relatively small amount of data corruption from bit errors in the data channel can effectively erase a watermark. At the same time, it is less likely that minor, intentional alterations will be detected.
There remains a need for a digital watermarking scheme that provides high watermark bit rates (relative to the overlying digital content) while remaining imperceptible to content users. A successful watermark would retain its signature in the presence of an error-prone data channel, and would correctly alert a watermark user to data tampering.
SUMMARY OF THE INVENTION
In accordance with the principles of the invention, there is provided digital watermarking that operates on a conventional digital video stream to etch, on hand, and read, on the other hand, digital watermarks in the stream that do not visibly interfere with the video content. The technique operates on digital data that has been transformed into the spatial-frequency domain, using inter-block differences between spatial-frequency coefficients to encode the bits of a digital watermark. According to the principles of the invention, it is possible to encode multiple watermark bits between two adjacent blocks, thus providing higher watermark data rates relative to underlying video content.
In one aspect, there is provided etching a digital watermark by: providing a watermark bit; providing a digital media stream comprising a first block and a second block, the first block comprising a first plurality of coefficients, and the second block comprising a second plurality of coefficients, each one of the second plurality of coefficients corresponding to one of the first plurality of coefficients; and setting a first difference to a predetermined value according to the watermark bit, the first difference being a difference between a first coefficient of the first block and a corresponding first coefficient of the second block.
This aspect may further include repeating the above for a plurality of consecutive watermark bits and a plurality of consecutive blocks, wherein the second block is used as a new first block, and a third consecutive block is used as a new second block. This aspect may also include setting the first difference to a predetermined value according to the watermark bit further includes forcing the first difference to a first level if the watermark bit is a one, and forcing the first difference to a second level if the watermark bit is a zero. In this aspect, the first level may be a binary even level and the second level may be a binary odd level. Setting the first difference to a binary even level may further include adding a quantization level to the corresponding first coefficient if the first difference is odd, and wherein setting the first difference to a binary odd level further includes adding a quantization level to the corresponding first coefficient if the first difference is even.
This aspect may further include: providing a second watermark bit; and setting a second difference to a predetermined value according to the second watermark bit, the second difference being a difference between a second coefficient of the first block and a corresponding second coefficient of the second block. The plurality of consecutive watermark bits may include an encrypted watermark. The digital media stream may include a Motion Picture Expert Group video stream, the first coefficient being a DC coefficient. The digital media stream may include a Motion Picture Expert Group video stream, the first coefficient being an AC coefficient.
In a different aspect, there is provided reading a digital watermark by: receiving a digital media stream comprising a first block and a second block, the first block comprising a first plurality of coefficients, and the second block comprising a second plurality of coefficients, each one of the second plurality of coefficients corresponding to one of the first plurality of coefficients; determining a first difference between a first coefficient of the first block and a corresponding first coefficient of t
Basch Evert
Lewis Arianne M.
Barrón Gilberto
McArdle Joseph M
Oliver, Esq. Kevin
Suchyta, Esq. Leonard C.
Verizon Laboratories Inc.
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