Authenticated Color Extended Visual Cryptography

Authenticated Blush Continued Beheld Cryptography with Absolute Reconstruction

R. Sathishkumar, Gnanou Florence Sudha

Abstract – Beheld Cryptography Arrangement (VCS) is an angel absorption arrangement which encrypts the abstruse argument based angel into assorted bifold images alleged shares, which are again transmitted to participants. These shares are again ample over by the participants to break the abstruse image, about with bargain quality. In Continued Beheld Cryptography Arrangement (EVCS), these bifold shares are encoded with awning images to accomplish allusive shares. In adjustment to enhance the decoded EVCS abstruse angel quality, Two in One Angel Abstruse Administration Arrangement (TiOISSS) was implemented, which offers absolute retrieval of the abstruse image. In this proposed scheme, the TiOISSS implemented for blush abstruse angel with allusive blush shares with absolute about-face is proposed. This arrangement uses Adaptive Halftoning address to advance the EVCS angel quality. Further, a blush accurate angel and a argument bulletin are encoded in the allusive blush shares to abolish any affected shares from the intruders, appropriately convalescent the aegis of the proposed scheme. Beginning after-effects characterize that the advance in affection and aegis of the scheme.

Index Terms – Angel Security, Beheld Cryptography Scheme, Adaptive Halftone, Polynomial Angel Abstruse Sharing,

I. Introduction

With the abrupt development in the networking technologies, agenda abstracts are transmitted beyond the apple over internet. Thus, aegis has become a basal affair in both advice and the circuitous encryption gives means to defended the advice from the intruders. Angel encryption has a basal role in array of applications like telemedicine, medical angel processing, aggressive applications, etc. In the acceptable way of encryption, the abstracts will be encrypted with a aegis key and the decryption charge be done with the aforementioned key. Hence, the aegis key is capital for able adaptation of the abstruse data.

VCS is one such encryption adjustment proposed by Naor and Shamir [1-2] to adumbrate a abstruse angel in the anatomy of n blatant pictures alleged shares such that the abstruse abstracts is retrieved by Animal Beheld Arrangement (HVS) by stacking the n shares. The acceptable VCS is airy for beginning VCS in which at atomic any k cardinal of shares are acceptable to break the abstruse angel [3-4]. The VCS has been proposed to adumbrate the gray images by appropriately halftoning it to bifold images [5-7]. These schemes were proposed with blatant shares, that may allure intruders’ attention.

R. Sathishkumar is with Department of Electronics & Advice Engineering, Perunthalaivar Kamarajar Institute of Engineering and Technology (PKIET), Karaikal, India. ([email protected])

Gnanou Florence Sudha is with Department of Electronics & Advice Engineering, Pondicherry Engineering College, Puducherry, India. ([email protected])

By suppressing this weakness, VCS were implemented with allusive shares from the awning images, and is referred as Continued Beheld Cryptography Arrangement (EVCS) [8-9].

The VCS has added been continued for accustomed blush images. Rijmen et al [10] proposed a VCS for blush abstruse angel with pixel expansion, in which anniversary abstruse blush pixel is broadcast into a block of 2×2 blush sub-pixels to accomplish two blush shares. Huo et al [11] proposed the VCS for gray-level and blush images application blush atomization and halftone technology, while application the advantage of acceptable connected beheld cryptography. Huo et al [12-13] proposed an bigger archetypal by application bifold encoding to represent the sub-pixel blocks. In [14], Huo et al adapted the adverse to acknowledge the abstruse angel with bigger quality, but the blatant shares acknowledge the clandestineness of the image. Der et al [15] proposed a blush VCS with an added accurate image, but the arrangement suffers from the beheld quality.

Polynomial angel abstruse administration (PISS) was implemented with absolute adaptation of abstruse angel [16]. In [17], Sian et al implemented a Two in One Angel Abstruse Administration Arrangement (TiOISSS) wherein the ambiguous abstruse angel is decoded application VCS in the 1st adaptation date and the bigger affection abstruse angel is decoded application PISS application computations. Peng et al [18] bigger the TiOISSS application GVCS with gray PISS ethics in the shares. Srividhya et al [19] bigger the TiOISSS angel affection by applying adaptive halftoning. However, the arrangement is implemented for gray images with blatant shares. In [20], TiOISSS was implemented for allusive shares, but the lossless accretion of the decoded angel was not achieved. The absolute archetypal of TiOISSS are implemented for gray images and generates blatant shares and that may allure the intruders to admit the affected shares.

In this proposed scheme, absolute TiOISSS [20] is continued for accustomed blush angel with RGB blush atomization method. Further, afore applying PISS algorithm, the blush abstruse angel is permuted at bit level, block akin and pixel akin to advance the security. This arrangement generates allusive shares based on the blush awning images. Additionally, a blush affidavit angel and a textual abstruse bulletin are aggregate to validate the actuality of the decoded abstruse image.

Experimental after-effects of the proposed arrangement appearance that the weaknesses of the absolute TiOISSS schemes are attempted, blush TiOISSS are implemented with the added affection and bigger security.

This cardboard is organized as follows. The VCS for gray calibration and blush images, TiOISSS and its accompanying works are discussed in area II. The proposed Accurate Blush VCS is discussed in area III. The beginning after-effects are discussed in area IV. The Affection assay and Aegis assay are discussed in area V and area VI. The cessation is presented in area VII.

II. Accompanying Works

The cold of the proposed arrangement is to extend the TiOISSS for blush images, with bigger affection and absolute reconstruction. This area discusses the accompanying works pertaining to absolute TiOISSS and its limitations.

  1. Visual Cryptography Scheme

Moni Noar and Adi Shamir implemented the beheld abstruse administration arrangement in 1994 [1], which requires computations alone in the encryption stage. The adaptation of abstruse angel is done by animal beheld arrangement (HVS).

In (k, n) beginning beheld abstruse administration scheme, n babble like shares are generated. Any k or added cardinal of shares are appropriate to break the abstruse image. With (k-1) or bottom shares, the abstruse cannot be reconstructed.

In basal (2, 2) VCS, every bifold abstruse angel pixel is broadcast into 2×2 sub-pixels in the 2 cardinal of blatant shares, as per the sub-pixel coding table apparent in Fig. 1. For every white pixelof the abstruse image, any one out of the six sub-pixels are about called for both the shares. Similarly, for every atramentous pixel of the abstruse image, any one out of the six sub-pixels are about called for allotment 1, and its acclaim sub-pixels for allotment 2.

Thus, by stacking the two shares, the white pixels are decoded with 50% gray level. However, the atramentous pixels are reconstructed with abounding atramentous sub-pixels. With the alone shares which has according allotment of white and atramentous pixels, the abstruse angel advice is not revealed. The allotment admeasurement and appropriately the reconstructed angel are angled due to pixel expansion.

Fig. 1 Sub-pixel coding table

  1. Adaptive Halftoning

Halftoning address is a action of converting the connected accent angel to connected angel or bifold image. The VCS is about ill-fitted for connected images. Many techniques like AM halftoning, FM halftoning, etc. are accessible for converting the gray calibration angel to bifold image. In [16-18], Error circulation based on FM halftoning with is implemented. But, this after-effects in broadcast white pixels in the abode of darker areas of gray image. The proposed assignment utilizes the Adaptive Halftoning [19] area in the dynamically bent beginning for halftoning, after-effects in bigger adverse for both consistently capricious images and aciculate alteration images. The animal eye perceives the tiny dots as white and denser dots as black, in the halftoned image. A gray calibration angel and its halftoned angel is apparent in Fig. 2.

Fig. 2 a) Continous accent b) Halftone

  1. Extended Beheld Cryptography Arrangement (EVCS)

The shares generated in the VCS bears a babble like image. Though, it may acknowledge no clue about the abstruse image, it may about accession suspicions about the secret. In adjustment to affected the weakness of babble like VCS shares, they are anchored with the alone awning images, appropriately breeding the allusive shares. The VCS with allusive shares are referred as Continued Beheld Cryptography Arrangement (EVCS). The allusive shares characterize the awning angel and not the abstruse image. However, on overlapping the allusive shares, the abstruse angel is decoded.

  1. Color Beheld Cryptography Scheme

Conventional VCS is applicative alone for bifold images. For grayscale image, it is to be halftoned to bifold angel as discussed in area II-B.

In the proposed scheme, adaptive halftoning is implemented. The blush angel is about constituted by either subtractive or accretion models as in Fig. 3.

Fig. 3 a) Subtractive model, and b) Accretion model

In the subtractive model, with primary blush apparatus as cyan (C), amethyst (M) and chicken (Y), the alternative colors can be acquired with able bond of CMY components. The blush printer is based on subtractive model.

In accretion model, the adapted blush is accomplished from able bond altered Red (R), Green (G) and Blue (B) blush components. By bond the RGB apparatus of according intensity, white blush can be obtained. Computer adviser is based on accretion model.

The abstruse blush angel can be addle into Red, Green and Blue frames. The alone frames will again be a gray arrangement of the agnate blush components. These frames are adaptive halftoned to access the bifold images which can be acclimated for bearing of shares in Red, Green and Blue components. By concatenating these RGB apparatus of anniversary shares, the agnate blush shares are obtained.

Overlapping the blush shares, the blush abstruse angel is decoded.

  1. Polynomial Angel Abstruse Administration Arrangement (PISSS)

PISS arrangement was aboriginal implemented [16] to adumbrate a abstruse image. Though, it contradicts the advantage of VCS, by involving algebraic calculations in both encrypting and decrypting stages, it offers absolute retrieval of the abstruse angel pixels. The PISS is implemented for TiOISSS with absolute about-face [20].

The polynomial in blueprint 1, encodes the angel pixels to blank data, which is again anchored in GVCS shares.

in which are the consecutive k pixels of the angel and P is the prime number.

In the adaptation phase, the Lagrange departure blueprint in blueprint (2) is acclimated to acquire the polynomial coefficients,

By substituting the pixel position for , where, , befitting as the variable, the polynomial coefficients is derived, Further, the adaptation polynomial blueprint can be acquired by from the polynomial accessory and the encoded angel pixels in blueprint (3).

The aboriginal abstruse pixel amount can be retrieved from the blueprint (3), by substituting the angel pixel position ,. A ample prime cardinal of 251, which is aural the gray pixel range, can be advised for encrypting the grayscale image.

  1. TiOISSS

Two in One Angel Abstruse Administration Arrangement (TiOISSS) [18] combines the claim of both PISS to accomplish absolute about-face & VCS to break the ambiguous abstruse angel by HVS. Hence, it involves two levels of encoding and adaptation phases.

The encoding appearance starts with breeding n VCS shares and n PISS shares from the aforementioned abstruse image, followed by replacing the atramentous pixels of VCS shares by the gray-valued pixels of PISS shares to accomplish GVCS shares, which are transmitted through n users. In the adaptation phase, the GVCS shares from the users are overlapped to reconstruct the ambiguous abstruse image, in the 1st date akin with aloof HVS. This action does not crave any algebraic computations. Further, Inverse PISS is activated to the gray pixels of GVCS shares to altogether retrieve the abstruse image, in the 2nd date akin of decoding.

III. Proposed scheme

In absolute TiOISSS [19], the blatant shares were generated, which accomplish allure the intruders to actualize a affected shares to coin the accepted user. In the proposed scheme, the absolute TiOISSS is adapted for blush images. The allusive blush EVCS shares are generated by embedding a blush affidavit image. The RGB apparatus of blush abstruse angel and the awning images are extracted as in Fig. 4. The adapted TiOISSS is activated for anniversary blush apparatus to accomplish the agnate the blush apparatus of GVCS shares. By concatenating the RGB components, blush GVCS shares are obtained.

The ambiguous blush abstruse angel and the affidavit angel can be decoded, in the aboriginal adaptation phase. Additionally, to accommodate added authenticity, a 216 $.25 of textual bulletin is anchored in the two LSBs of white pixels of all GVCS shares, which are again decoded in the 2nd phase. The RGB apparatus of blush abstruse angel and the affidavit angel are again retrieved by applying Inverse PISS. The stages complex in the proposed adapted blush TiOISSS with the bearing of allusive EVCS shares and including an affidavit angel are discussed in the afterward sections.

  1. EVCS Allotment generation

EVCS shares are generated from the alone RGB apparatus of the abstruse blush image, affidavit angel and the awning image. The Larboard bisected of the abstruse angel is advised for breeding the larboard bisected of VCS shares (LS1 and LS2) as in Fig. 5. By because the affidavit image, the appropriate bisected of VCS shares (RS1 and RS2) are generated.

For anniversary RGB apparatus of the abstruse image, the afterward accomplish are followed to accomplish the agnate RGB apparatus of the VCS shares.

1.From the larboard bisected of abstruse angel (LS), the larboard bisected of share1 (LS1) and the larboard bisected of share2 (LS2) are generated.

2.For every atramentous pixel of the halftoned affidavit image, agnate subpixels of larboard bisected of allotment 2 (LS2) with one pixel adapted from white to atramentous is placed in the agnate subpixel area of appropriate bisected of allotment 1 (RS1). Thus, the RS1 and LS2 will break the ambiguous affidavit image.

3.For anniversary atramentous pixels of RS, the agnate sub-pixels of the appropriate bisected of allotment 1 (RS1) with adapted area of atramentous pixels is placed in the agnate subpixel area of appropriate bisected of allotment 2 (RS2).

4.VCS shares are acquired by accumulation the larboard bisected and the appropriate bisected of anniversary shares.

To affected the weakness of blatant shares, awning images are anchored to accomplish the allusive shares. Anniversary RGB apparatus of the VCS shares are candy as apparent in Fig. 5, with the agnate RGB apparatus of the awning images. For every atramentous pixel in anniversary awning angel component, the agnate sub-pixel area of the agnate VCS allotment basic is adapted such that one white pixel adapted to black. The area of the adapted atramentous pixel depends on the pixel amount of the abstruse angel in the agnate location. Thus, the EVCS shares apparatus are generated from the VCS shares and the awning images.

  1. GEVCS Allotment generation

The blush abstruse angel is aboriginal addle into RGB apparatus and the pixels of anniversary basic are permuted in three levels to advance the security. In the proposed scheme, the 128 bit of encryption key is acclimated as formatted in Fig. 6 is acclimated to accomplish the about-face in bit level, block akin and pixel akin with agnate 32-bit keys. The about-face adjustment key defines the adjustment of about-face performed which is appropriate in about-face about-face operation. The GVCS allotment adjustment defines the allotment adjustment to be candy to retrieve the anchored key from the GVCS shares. The admeasurement of the textual abstruse bulletin anchored in the GVCS shares is authentic in the 16-bit Abstruse Bulletin length.

The PISS shares are generated from the permuted blush abstruse angel as abundant in area II-E. The resultant PISS ethics and the affidavit blush angel pixels are anchored into the atramentous sub-pixels are the EVCS shares. Prior to embedding these PISS values, it is truncated by a agency α, (α = 1, 2, … 16). This truncated amount forth with its butt in GEVCS shares will be darker abreast to black, accouterment bigger beheld quality. Thus, the truncated permuted PISS values, the blush accurate angel and the textual abstruse bulletin are anchored into EVCS shares to accomplish the GEVCS shares as abundant in the Fig.7.

  1. Decryption of the Abstruse image

The adaptation of the abstruse angel is done in two phases. In the aboriginal phase, the two GEVCS shares are overlapped to break the ambiguous blush abstruse image. To verify its authenticity, RS1 and LS2 of the GEVCS shares are superimposed to break the affidavit image.

In the added appearance of decoding, the encryption keys and the abstruse letters are extracted from the white pixels of anniversary GEVCS shares. The PISS ethics are retrieved from the GEVCS shares. Inverse PISS is activated to reconstruct the abstruse angel and the affidavit angel are perfectly. The action is explained in Fig.8.

IV. Beginning Results

The beginning after-effects of the proposed Accurate Blush Continued TiOISSS with absolute about-face are discussed in this section. This arrangement is implemented for truncation factor, α = 7 and adaptive halftoning address is activated for VCS allotment generation.

The 256×256 sized blush abstruse angel and the 256×128 sized blush affidavit angel are advised as apparent in Fig. 9(a) & 9(b). The blush awning images of 256×256 admeasurement are apparent in Fig. 9(c) & 9(d). The Adaptive halftoning adaptation of the abstruse angel and awning images are apparent in Fig. 9 (e), 9(f) & 9 (g). Applying VCS over the halftoned affidavit and the abstruse angel with pixel expansion, m = 4, two VCS shares of 512×512 are generated and is apparent in Fig. 9 (h) & 9 (i). The GVCS shares generated from VCS shares by embedding PISS ethics as abundant in area III-B are apparent in Fig. 9 (j) & 9 (k).

In the aboriginal akin of decoding, the two GEVCS shares are overlapped to break the ambiguous blush abstruse image. To verify the authenticity, LS2 and RS1 are overlapped to acknowledge the ambiguous affidavit image. They are apparent in Fig. 9 (l) & 9 (m). In the 2nd adaptation phase, by applying Inverse PISS and about-face about-face over the extracted gray pixels of the GEVCS shares, the absolute about-face of both the blush affidavit angel and the blush abstruse angel is decoded as apparent in Fig. 9 (n) & 9 (o).

V. Affection Analysis

The ambit like Contrast, Structural Affinity Index Admeasurement (SSIM) & Peak Signal to Babble Ratio (PSNR) of the Accurate Blush Continued TiOISSS are analysed.

  1. Contrast

Contrast which represents the beheld affection of the image, is accustomed by the normalized aberration amid the beggarly grayness of the white abstruse pixels and the beggarly grayness of atramentous abstruse pixels in the decoded image. In this scheme, adverse [20] is affected amid the accumulation of decoded pixels admired added than the threshold, (C0) and the accumulation of decoded pixels admired bottom than the threshold, (C1) and is accustomed by,

Contrast amid the blush abstruse angel and its 1st decoded abstruse angel for adaptive halftoning address and amid the affidavit angel and its 1st decoded achievement has been tabled in Table I for assorted truncation factor, α. The adverse is improved

  1. SSIM

It is a admeasurement of affinity amid two images and it is affected for two accepted sized (NÃ-N) windows x and yof the two images. SSIM is accustomed by


and are the boilerplate of y and x.

and are the about-face of x and y, is the covariance of x and y

and are two variables to balance the division, L is the activating ambit of the pixel ethics and and by default.

The SSIM amid the blush abstruse angel and its 1st decoded abstruse angel for adaptive halftoning address and amid the affidavit angel and its 1st decoded achievement has been tabled in Table I for assorted truncation factor, α. The SSIM is bigger consistent in added affinity amid the abstruse angel and the decoded abstruse image.

  1. PSNR

The Peak Signal to Babble Ratio (PSNR) is a admeasurement to appraisal the angel affection amid two images. Based on the pixel aberration amid the reconstructed angel and the aboriginal image, PSNR is authentic as

where MSE denotes Beggarly Squared Error and s = 255, the best pixel amount of the image.

The PSNR amid the blush abstruse angel and its 1st decoded abstruse angel for adaptive halftoning address and amid the affidavit angel and its 1st decoded achievement has been tabled in Table I for assorted truncation factor, α. The PSNR is college for bottom amount of the truncation factor.


Comparison of Abstruse Angel and 1ST PHASE DECODED Abstruse Image

Secret angel vs Decoded Abstruse angel (1st phase)

Auth angel vs Decoded Auth angel (1st phase)









Not possible, No Truncation

Not possible, No Truncation






































































































Table II shows the allegory of allusive shares with the agnate awning images, which depicts that allusive shares offers bigger beheld quality.


Parameter Allegory for GVCS Shares vs Awning Images, for α = 7

Proposed Scheme












Table III shows the allegory of altered halftoning techniques, which shows that the adaptive halftoning offers bigger beheld quality.


Parameter Allegory amid the Abstruse Angel and 1st decoded Abstruse Image, for Altered Halftoning, for α = 7

Halftoning Technique

AM Halftoning

FM Halftoning

Adaptive Halftoning

% Improvement

FM vs Adaptive
















VI. Aegis Analysis

The aegis of the proposed arrangement is discussed actuality with the afterward aegis aspects.

  1. Authentication angel for added security

With any one of the GEVCS blush shares, the hackers may accomplish the alternative affected shares, such that the accepted receiver may get a artificial abstruse angel instead of the aboriginal abstruse image. To affected this weakness, a blush affidavit angel is encoded into the GEVCS shares. In the 1st akin of decoding, the ambiguous affidavit angel is reconstructed and is acclimated to validate the actuality of the abstruse image, appropriately acceptable the aegis of the scheme. Further, the absolute retrieval of the affidavit angel is accomplished by computations, in the 2nd adaptation phase.

  1. Histogram of Shares

Fig. 10 shows the histogram arrangement of the blush GEVCS allotment 1, for truncation agency α = 7. It can be empiric that the pixels absorb amount up to 36 (i.e. 28/α) and at 255. By allotment altered ethics of α, the pixel administration of GEVCS shares can be bound accordingly. Unlike the aboriginal abstruse image, area pixels are broadcast over the absolute range, GEVCS shares are anchored with bound pixel distribution, appropriately enhancin

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