1. International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 9 No.26 (2014) pp. 9323-9326
© Research India Publications; http://www.ripublication.com/ijaer.htm
Comparative Study of Watermarking and Encryption
Schemes for JPEG2000 Images
.J.Jereesha Mary, 2
S.Sebastin Antony Joe,
3
Dr.C.Seldev Christopher
Abstract: The need for secured digital data is getting more intense
and hence there is a necessity for ownership verification, tamper
proof and data integrity. As a solution for these, digital
watermarking methods may be used. In this paper, three
watermarking schemes namely Spread Spectrum (SS), Scalar
Costa scheme Quantization Index Modulation (SCS_QIM),
Rational Dither Modulation (RDM) and the encryption techniques
like RC4,RC5,RC6 which are responsible for the robustness of the
above said watermarking system for JPEG2000 images are
compared. The Peak Signal to Noise Ratio (PSNR) and the Mean
Square Error (MSE) for different watermark images have been
compared and presented in this paper.
Keywords – RC4, RC5, RC6, Spread Spectrum, Scalar Costa Scheme
Quantization Index modulation, Rational Dither
Modulation,JPEG2000.
INTRODUCTION
Digital media communication and security for the digital
content has seen a rapid growth in the current era. Digital Asser
Management Systems (DAMS) are intended to work with
compressed and encrypted data. Media contents liketext, image,
audio, video, etc., can be secured using digital watermark
techniques. Watermarking is a method that is used for reducing
counterfeiting in which the watermark is embedded inside the
message. This watermark can then be extracted or detected for
variety of purposes. Image authentication with watermarking
schemes was proposed by many researches in order to overcome
the drawbacks of image authentication using digital signature
schemes. In the latter scheme the modification of image or
tampering can be identified,but the exact location of
modification cannot be found [1-4]. Fridrich [5] proposed a
block cipher method to prevent collage attack and Wong [6]
proposed a public key fragile watermarking scheme for image
authentication which was vulnerable to vector quantization
attack. This was proven by Memon[7] and hence
WongandMemon[8] proposed an improved model to reduce
vector quantization attack. The above said methods are for JPEG
compressed images.
In this paper, we present a comparative study on various
watermarking schemes like spread spectrum, SCS-QIM, RDM
and the encryption methods used in coordination with those
watermarking schemes for JPEG2000 images. Compressed
images are mainly used in digital watermarking algorithms.
Watermarking algorithms are said to be effective if the
embedded watermark is robust against compression. The
encryption is done in the compressed JPEG2000 image except
the header and marker segment [9]. JPEG2000 images are being
used, since the decompression can be made at any ratio for the
same compression ratio [10]. There aremany encryption
algorithms proposed to work with watermarking algorithms.
Using asymmetric schemes with homomorphic property, the
RSA, Elgamel, Goldwasser-Micali, Paillierhave their own
drawbacks like, the ciphertext output results in loss of
compression efficiency if the message size is small and if the
message size is large the compression loss is reduced, but the
payload capacity decreases [11-14]. To overcome this
Subramanyam et al. in [15] proposed RC4 symmetric stream
cipher scheme with homomorphic property to achieve copyright
protection. Gayathri I.K. proposed the symmetric block cipher
RC5 [16] to work with the watermarking schemes used in [15].
RC5 is more secure and robust than RC4 due to its increased
number of rounds. RC6 is being used by Kukoo Anna Mathew
[17] instead of RC5 due to its increased use of registers.
II. TECHNICAL BACKGROUND
The watermarking schemes used to provide robustness and
the encryption schemes to secure the JPEG2000 images for copy
right protection and content authentication are listed below.
JPEG2000 standard
JPEG2000 is a compression standard that is based on
wavelet technology. Scalability and editability are its main
advantage. It meansfor a single encoding resolution, it can be
decoded at any resolution. Hence it needs computationally
complex encoders and decoders. JPEG2000 supports very low
and very high compression rates. It define both the file formats
and code streams. In JPEG2000 compression technique, the
color components of the input are transformed using irreversible
color or reversiblecolor transform. The output is tiled and then
wavelet transformed to an arbitrary depth using irreversible
orreversibletransform. It is then quantized and coded using
Embedded Block Coding with Optimized Truncation (EBCOT)
scheme to get the compressed output [18].The JPEG2000
compression standard processesthe output as byte streams.
Encryption Schemes
Encryption algorithms are used in co-ordination with the
watermarking schemes to make the JPEG2000 images more
robust so that it provides ownership verification & content
authentication.Various encryption schemes are discussed below,
RC4

2. International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 9 No.26 (2014)
© Research India Publications; http://www.ripublication.com/ijaer.htm
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RC4 is a symmetric stream cipher with homomorphic
property. RC4 generates a pseudorandom stream of bits (a
keystream). As with any stream cipher, these can be used for
encryption by combining them with the plaintext using bit-wise
Exclusive-OR. Encryption is done in the input image byte by
byte. This is shown as,
C=E(M,Ks)
C =(mi + ki) mod 255 i = 0,1,2. . . .L-1
WhereM - Input image
C -cipher text
E - Encryption algorithm
Ks -key
Key generation is an important part in RC4 in which a secret
valueSvsharable by both the encryption and decryption side is
applied to RC4 which in turn generates the key stream ks[19].
RC5
RC5 is a homomorphic, symmetric-key block cipher which
has a variable block size (32, 64 or 128 bits), key size (0 to 2040
bits) and number of rounds (0 to 255).RC5 uses two registers
and modular addition. Key schedule is a complex part in RC5
[20].
A = A + S[0];
B = B + S[1];
for i = 1 to r do
A= ((A Xor B) <<< B) + S[ 2 * i ]
B = ((B Xor A) <<< A) + S[ 2 * i + 1]
Where
A, B - two w-bit words of the input in input registers
S - Expanded key table
RC6
RC6 is a symmetric keyblock cipher derived from RC5. Like
RC5, it can be parameterized to support a wide variety of word-
lengths, key sizes and number of rounds. But RC6 does include
the use offour working registers instead of twoand uses an extra
integer multiplication operation in order to make the rotation
dependent on every bit in a word, and not just the least
significant few bits.The encryption process is composed of three
stages viz., pre-whitening, inner loop of rounds, and post-
whitening. Plaintext revealing part of the input to the first round
and the ciphertext revealing part of the input to the last round of
encryption are removed bypre-whitening and post-
whitening.The operations used in RC6 are defined as followings
[21].
A+B integer addition modulo 2w
A-B integer subtraction modulo 2w
A⊕B bitwise exclusive-or of w-bit words
A x B integer multiplication modulo 2w
A⋘B rotation of the w-bit word A to the left by theamount
given by the least significant log w bits ofB
A⋙B rotation of the w-bit word A to the right by theamount
given by the least significant log w bits ofB
(A,B,C,D)=(B,C,D,A) parallel assignment.
Watermarking Algorithms
Watermarking algorithms are used to embed the watermark
inside the input image. The watermarking algorithm should be
robust for ownership verification and fragile for content
authentication.Image watermarking process should be one
without having any visual artifacts between the original and the
watermarked image. Few watermarking schemes are being
discussed below.
Spread Spectrum (SS)
Spread spectrum system has thetransmitted signal spread
over a wide frequency band.The codes are unique to every user
and have low cross correlation value. The main advantage of
spread spectrum is it blocks purposeful and
accidentalinterference. Since it uses pseudo random code
sequence, the privacy of the code is maintained [22]. The
watermarked vector may be expressed as
Wv= S + W
Where
Wv- Watermarked vector
S- Signal vector
W- Watermark vector
Both S and W are in the same vector space R
Scalar costa scheme(SCS)
Scalar costa scheme is a technique for embedding that
belongs to quantization based methods and it uses scalar
approach and reception function [23]. In scalar costa scheme the
Lx – dimensional codebook of costa scheme is replaced by a
product codebook that contains scalar quantizer of uniform step
size . The watermarked data is given as
Wm = M +W=M+ α (Qi(M)-M)
Where,
Wm- Watermarked sequence.
M - Message
W - Watermark sequence
α- Scalar factor / Distortiioncompensation parameter
Qi(M) - Quantization value of M using step size D.
Rational Dither Modulation (RDM)
RDM is a modification of Dither Modulation (DM) which
overcomes the vulnerability of scaling attack. It does not focus
on the step-size of the quantizer and hence avoids the usage of
pilot-sequence. It is used for carrying outscalar operation and
hence avoids the construction of spherical codes. RDMuses
gain-invariant adaptive quantization step-size at both embedder
and decoder. This causes the watermarked signal being
asymptotically stationary [25]. The embedding rule is given as
follows
where
yk- vector with„L‟ past samples of vector „y‟
g- isa function, that satisfies
with
-Quantiers
III. SECURITY OF CRYPTOSYSTEM
RC4
₳

3. International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 9 No.26 (2014)
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RC4 crypto system has the advantage of being faster and it is
suitable for streaming application [19].[26] proved that
relatively low sampling resistancein RC4 will increase the
probability of data tradeoff attacks based on the key scheduling
algorithm. Also the RC4 algorithm is weak in common mode of
operation and is commonly used in Wired Equivalent Privacy
Protocol (WEP).
RC5
RC5 algorithm is simple. The data dependent rotations and
the complexity in key scheduling are its advantages [27]. RC5-
32algorithm (32-bit blocks) is susceptible to known plain text
attack which is linear.From[28]it is shown that RC5-32 has a
factor of approximately 26
to attack an extra round and RC5-64
has around 28
.RC5-64 algorithm (64-bit blocks)is prone to
differential attack, when the chosen plain text is 244
. But it
overcomes the attack with 18 – 20 rounds.
RC6
RC6 is also susceptible to differential linear attack as that of
its predecessor RC5[28]. Linear attack is possible with 16
rounds with text size 2119
. With less than 15 rounds it undergoes
statistical attack [29]. RC6 is affected by X2
attack when the
number of rounds is more than 16[30]
IV. ROBUSTNESS OF EMBEDDING ALGORITHM
Spread Spectrum
An attack on spread spectrum watermarks based on
estimation of the watermarks is explained in [31]. Various
attacks that spread spectrum watermarking prone to are simple
attacks, detection disabling attacks, ambiguity attack, removal
attack etc.
Scalar Costa Scheme with QIM
Under AWGN attack the performance of Scalar Costa
Scheme is high compared to spread spectrum. Sospread
spectrum is of no use even when the watermark must survive
high noise level [24]. For high noise levels independent of the
host statistics and the document to watermark ratio the
achievable embedding rate of scalar costa scheme is smaller
than spread spectrum. When the watermark to noise ratio
increases, the scalar costa scheme outperforms spread spectrum
[24].
Rational Dither Modulation
Rational Dither Modulation has higher capacity than spread
spectrum and scalar costa scheme. It has benefits from the gains
afforded by distortion compensation and channel coding.
Moderately it is robust to Invariant value metric scaling attack
[25]. The RDM as in [25] poorly models the human perceptual
system and a function that models the properties of perception
should be considered [32]
V. CONCLUSION
The above comparative study discloses that a number of
watermarking and encryption schemes can be used for different
watermarking applications. The watermarking schemes
compared are robust and they can be used for content
authentication. The encryption algorithms which are explained
in this paper can be used in addition to the watermarking
schemes and can be applied for copy right protection. The
advantages and drawbacks the major water marking / encryption
schemes are being discussed here. The watermarking schemes
can all be together used with a single encrypion algorithm. The
research work can be extended to find a suitable encryption
scheme and watermarking algorithm to be put together to give a
robust watermarking for JPEG2000 images.
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