DATA HIDING IN ENCRYPTED H.264 VIDEO FORMAT

ALPHIN J THOTTUPATTU
CB.EN.P2CSP14001
DATA HIDING IN ENCRYPTED H.264/AVC VIDEO
STREAMS BY CODEWORD SUBSTITUTION

INTRODUCTION
 H.264/AVC -most widely deployed video coding
standard
 Data hiding directly in compressed and
encrypted bitstream
 Technique to preserve file-size and maintaining
the video quality while hiding data

Needs
 Avoid the leakage of video content
 Cloud server can embed the additional information
Eg. : medical videos or surveillance videos
 Authentication
 Provision of protection of intellectual property rights
 Indication of content manipulation

Comparison with other
techniques
 Walsh-Hadamard transform based
imagewatermarking
 Encryption by using bit-XOR operation
 A low cost fragile watermarking scheme in
H.264/AVC
compressed domain
 content-based H.264/AVC authentication
 Joint data-hiding and encryption approaches
 Combined scheme of encryption and watermarking
 Difficulties to transplant the existing data hiding
algorithms to the encrypted domain

Challenges for direct data
hiding…
 Determine where and how the bitstream can
be modified
 Insure high visual fidelity
 maintain the file size
 Hidden data can be extracted either from the
Encrypted or decrypted video stream

THE PROPOSED SCHEME
EXCELLENT PERFORMANCE IN
 The data hiding is performed directly
 Ensure format compliance
 Strict file size preservation
 Extracting the hidden data either from the
encrypted or decrypted video

PROPOSED SCHEME
 H.264/AVC video encryption
-standard stream ciphers with
encryption keys
 data embedding
-codeword substituting
 data extraction

DATA HIDING IN ENCRYPTED H.264 VIDEO FORMAT

Encryption of H.264/AVC Video
Stream
 Encrypt code words of
1. IPM
2. residual data
3. motion information (MVD)
 Security, efficiency, and format compliance
 Encrypted bit stream is still H.264/AVC
compliant can be decoded

Intra-Prediction Mode (IPM)
Encryption
 Intra-coded blocks can now be predicted from
neighbouring blocks
 Only the difference between the predicted and
coded block needs to be encoded
 Encrypt IPM codeword without modifying the
CBP
 keep the codeword’s length unchanged

Intra_4 × 4 luminance block Intra_16 × 16 block

Motion Vector Difference (MVD)
Encryption
 Protect both texture information and motion
information
 Exp-Golomb entropy coding
 - as[M zeros] [1] [INFO]
 every frame of the video needs to be coded
independently as a new image

Residual Data Encryption
 residual data in both I-frames and P-frames should be
encrypted
 Encrypting based on the characteristics of codeword
 CAVLC entropy coding
 -{Coef f token, Sign of TrailingOnes, Level, Total zeros,
Run bef ore}
 modifying the code words of Sign_of_TrailingOnes and
Level

Data Embedding
 Since the sign of Levels are encrypted, data
hiding should not affect the sign of Levels
 Must remain syntax compliance so that it can be decoded by
standard decoder.
 Keep the bit-rate unchanged should have the same size as the original
codeword.
 Data hiding does cause visual degradation
 Embedded data after video decryption has to
be invisible to a human observer

Data hiding
 Code words of Levels 2 and 3 within P-frames
are used for data hiding
 Steps
 Step1. The additional data is encrypted with the
chaotic pseudo-random sequence
 Step2. The codewords of Levels are obtained by
parsing the encrypted H.264/AVC bitstream

Data hiding
Step3 .
 Step4. Choose the next codeword
and then go to Step3 for data hiding.

Data extraction
Fast and simple
Scheme 1-Encrypted Domain Extraction
 Step1: The code words of Levels are firstly identified
by
parsing the encrypted bit stream.
 Step2:
 If the codeword belongs to code space C0, the
extracted data bit is “0”
extracted data bit is “1”.
 Step3: extracted bit sequence could be decrypted

Data extraction
Scheme 2-Decrypted Domain Extraction
 Step1: Generate encryption streams
 Step2: The code words are identified by parsing the
encrypted bit stream.
 Step3: XOR operation
 Step4:
 Step3: extracted bit sequence could be decrypted

Scheme 1-Encrypted Domain
Extraction
Scheme 2-Decrypted Domain
Extraction

Security of Encryption Algorithm
 Secure stream cipher encrypt the bit stream and
chaotic pseudo-random sequence for additional
data
-Cryptographic security
 Encrypts IPM, MVD and residual coefficients
- Perceptual security

Visual Quality of Stego Video
 visual quality of the decrypted video containing
hidden data is very close to that of the original video
 only the code words of Levels within P-frames are
modified for data hiding

Results to evaluate the perceptual
quality

Embedding Capacity
Data hiding payload can be assessed in kilobits per second
(kbits/s)
Embedding capacity determined by the no. of qualified code
words

Bit Rate Variation
BR_em -bit rate generated by encryption and data
embedding encoder
BR_orig -bit rate generated by the original encoder.
The bit rate of the encrypted and stego video
remains unchanged.

Applications
 cloud computing
 a database manager may embed the personal information into
medical videos or surveillance
videos
 video notation, or authentication data
 protection of intellectual property rights
 Indication of content manipulation
 Forensic analysis

CONCLUSION
 embed additional data in encrypted H.264/AVC format

 encryption, data embedding & data extraction phases
 can preserve the bit-rate exactly even after encryption
 data hiding entirely in the encrypted domain & data
extraction either in encrypted or decrypted domain
 preserve file-size and only small degradation in
video quality

References
[1] W. J. Lu, A. Varna, and M. Wu, “Secure video processing: Problems and
challenges,” in Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing,
Prague, Czech Republic, May 2011, pp. 5856–5859.
[2] B. Zhao, W. D. Kou, and H. Li, “Effective watermarking scheme in
the encrypted domain for buyer-seller watermarking protocol,” Inf. Sci.,
vol. 180, no. 23, pp. 4672–4684, 2010.
[3] P. J. Zheng and J. W. Huang, “Walsh-Hadamard transform in the
homomorphic
encrypted domain and its application in image watermarking,”
in Proc. 14th Inf. Hiding Conf., Berkeley, CA, USA, 2012, pp. 1–15.
[4] W. Puech, M. Chaumont, and O. Strauss, “A reversible data
hiding method for encrypted images,” Proc. SPIE, vol. 6819,
pp. 68191E-1–68191E-9, Jan. 2008.
[5] X. P. Zhang, “Reversible data hiding in encrypted image,” IEEE Signal
Process. Lett., vol. 18, no. 4, pp. 255–258, Apr. 2011.

References
[6] W. Hong, T. S. Chen, and H. Y. Wu, “An improved reversible data
hiding in encrypted images using side match,” IEEE Signal Process.
Lett., vol. 19, no. 4, pp. 199–202, Apr. 2012.
[7] X. P. Zhang, “Separable reversible data hiding in encrypted
image,” IEEE Trans. Inf. Forensics Security, vol. 7, no. 2,
pp. 826–832, Apr. 2012.
[8] K. D. Ma, W. M. Zhang, X. F. Zhao, N. Yu, and F. Li, “Reversible data
hiding in encrypted images by reserving room before encryption,” IEEE
Trans. Inf. Forensics Security, vol. 8, no. 3, pp. 553–562, Mar. 2013.
[9] A. V. Subramanyam, S. Emmanuel, and M. S. Kankanhalli, “Robust
watermarking of compressed and encrypted JPEG2000 images,” IEEE
Trans. Multimedia, vol. 14, no. 3, pp. 703–716, Jun. 2012.
[10] S. G. Lian, Z. X. Liu, and Z. Ren, “Commutative encryption and
watermarking in video compression,” IEEE Trans. Circuits Syst. Video
Technol., vol. 17, no. 6, pp. 774–778, Jun. 2007.

 A video coding format[1] (or sometimes video
compression format) is a content representation
format for storage or transmission of digital video
content (such as in a data file or bitstream). Examples
of video coding formats include MPEG-2 Part 2,
MPEG-4 Part 2, H.264 (MPEG-4 Part 10), HEVC,
Theora, Dirac, RealVideo RV40, VP8, and VP9. A
specific software or hardware implementation capable
of video compression and/or decompression to/from a
specific video coding format is called a video codec;
an example of a video codec is Xvid, which is one of
several different codecs which implements encoding
and decoding videos in the MPEG-4 Part 2 video
coding format in software

 A video coding format does not dictate all
algorithms used by a codec implementing the
format. For example, a large part of how a video
compression typically works is by finding
similarities between video frames (block-
matching), and then achieving compression by
copying previously-coded similar subimages (e.g.,
macroblocks) and adding small differences when
necessary. Finding optimal combinations of such
predictors and differences is an NP-complete
problem,[2] meaning that it is practically impossible
to find an optimal solution.

 One subclass of relatively simple video coding
formats are the intra-frame video formats, in
which compression can only be done to each
picture in the video-stream in isolation, and no
attempt is made to take advantage of
correlations between successive pictures over
time for better compression.
 A level is a restriction on parameters such as
maximum resolution and data rates

In the field of video compression a video frame is compressed using different
algorithms with different advantages and disadvantages, centered mainly around
amount of data compression. These different algorithms for video frames are called
picture types or frame types. The three major picture types used in the different
video algorithms are I, P and B. They are different in the following characteristics:
I-frames are the least compressible but don't require other video frames to decode.
P-frames can use data from previous frames to decompress and are more
compressible than I-frames.
B-frames can use both previous and forward frames for data reference to get the
highest amount of data compression.
An I-frame is an 'Intra-coded picture', in effect a fully specified picture, like a
conventional static image file. P-frames and B-frames hold only part of the image
information, so they need less space to store than an I-frame and thus improve video
compression rates.
A P-frame ('Predicted picture') holds only the changes in the image from the previous
frame. For example, in a scene where a car moves across a stationary background,
only the car's movements need to be encoded. The encoder does not need to store
the unchanging background pixels in the P-frame, thus saving space. P-frames are

Intra coded frames/slices (I-frames/slices or Key frames)
See also: Key frame (animation) and Intra-frame
I-frames are coded without reference to any frame except themselves.
May be generated by an encoder to create a random access point (to allow a decoder to
start decoding properly from scratch at that picture location).
May also be generated when differentiating image details prohibit generation of effective
P or B-frames.
Typically require more bits to encode than other frame types.
Often, I-frames are used for random access and are used as references for the
decoding of other pictures. Intra refresh periods of a half-second are common on such
applications as digital television broadcast and DVD storage. Longer refresh periods
may be used in some environments. For example, in videoconferencing systems it is
common to send I-frames very infrequently.
Predicted frames/slices (P-frames/slices)
Require the prior decoding of some other picture(s) in order to be decoded.
May contain both image data and motion vector displacements and combinations of the
two.
Can reference previous pictures in decoding order.
Older standard designs (such as MPEG-2) use only one previously decoded picture as a
reference during decoding, and require that picture to also precede the P picture in
display order.
In H.264, can use multiple previously decoded pictures as references during decoding,
and can have any arbitrary display-order relationship relative to the picture(s) used for its
prediction.
Typically require fewer bits for encoding than I pictures do.

 An I-frame is a compressed version of a single
uncompressed (raw) frame. It takes advantage
of spatial redundancy and of the inability of the
eye to detect certain changes in the image.
Unlike P-frames and B-frames, I-frames do not
depend on data in the preceding or the
following frames. Briefly, the raw frame is
divided into 8 pixel by 8 pixel blocks. The data
in each block is transformed by the discrete
cosine transform (DCT).

DATA HIDING IN ENCRYPTED H.264 VIDEO FORMAT

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DATA HIDING IN ENCRYPTED H.264 VIDEO FORMAT