Visual Cryptography

VISUAL CRYPTOGRAPHY Dr. Qaim Mehdi Department of Computer Science

What is Cryptography?

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Cryptography is the science of information security.

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The main objective of cryptography is information hiding.

What is Cryptography?

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Cryptography is the science of information security.

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The main objective of cryptography is information hiding.

History of Cryptography-1: Hieroglyphics

Cryptography probably began in or around 2000 BC in Egypt, where hieroglyphics were used to decorate the tombs of deceased rulers and kings.

COMPUTER SCIENCE

History of Cryptography-2: Wax Tablet

A wax tablet is a tablet made of wood and covered with a layer of wax. It was used as a reusable and portable writing surface in the 1400 BC.

History of Cryptography-3: Caesar Cipher

The first known use of a modern cipher was introduced by Julius Caesar (100 BC to 44 BC), who did not trust his messengers when communicating with his governors.

Failure is success if we learn from it.

Idloxuh lv vxffhvv li zh ohcuq iurp lw.

Visual Cryptography

It is a new type of cryptographic scheme, which can decode concealed images without any cryptographic computations. The scheme is perfectly secure and very easy to implement.

Visual Cryptography

It is a new type of cryptographic scheme, which can decode concealed images without any cryptographic computations. The scheme is perfectly secure and very easy to implement.

Moni Naor is a computer scientist and also famous for his Turing Test on verification of a human in the loop.

Adi Shamir is a cryptographer and co-inventor of the famous RSA algorithm.

Pixel Pixel is the smallest addressable element in a picture element.

Grayscale-level Grayscale Level is the brightness value assigned to a pixel; values range from black, through gray, to white.

Qualified Participants A qualified set of participants is a subset of ÎĄ whose shares visually reveal the 'secret' image when stacked together.

Qualified Participant

Qualified Participant

Forbidden Participant

Qualified Participants A forbidden set of participants is a subset of ÎĄ whose shares reveal absolutely no information about the 'secret' image when stacked together.

Forbidden Participant

Qualified Participant

Qualified Participant

Visual Cryptography: The Objective

Encrypting written material (printed text, handwritten notes, pictures, etc.) in a perfectly secure way which can be decoded directly by the human visual system.

Visual Cryptography: The Approach

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The message consists of a collection of black and white pixels and each pixel is handled separately.

Each original pixel appears in n modified versions (called shares), one for each transparency.

Visual Cryptography: The Approach

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The message consists of a collection of black and white pixels and each pixel is handled separately.

Each original pixel appears in n modified versions (called shares), one for each transparency.

Horizontal Share

Vertical Share

Diagonal Share

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Visual Cryptography: The Process

Original Pixel Share 1 Share 2 Overlaid

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Visual Cryptography: The Process

Original Pixel

1

0

Share 1

0 1

0 1

Share 2

1 0

0 1

Overlaid

1

0 1

Illustration of Visual Cryptography

Pixel (0)

Pixel (1)

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Illustration of Visual Cryptography

pixel

m sub-pixels

Example. n = 2, m = 4 or

n shares

or

m sub-pixels

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Illustration of Visual Cryptography horizontal shares

Secret Message

vertical shares

diagonal shares

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Illustration of Visual Cryptography horizontal shares

vertical shares

diagonal shares

Concluding Remarks

Concluding Remarks

Future Scope ď ś ď ś

We can improve result by removing digital noise(gray-shades).

With some minor changes, we can implement visual cryptography on color images.

References 

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M. Naor and A. Shamir, Visual cryptography, in "Advances in Cryptology { EUROCRYPT '94", A. De Santis, ed., Lecture Notes in Computer Science 950 (1995), 1-12.

G. Ateniese, C. Blundo, A. De Santis and D. R. Stinson, Visual cryptography for general access structures, Information and Computation 129 (1996), 86-106.

C. Blundo, A. Giorgia Gaggia and D. R. Stinson, On the dealer's randomness required in secret sharing schemes, Designs, Codes and Cryptography 11 (1997), 107-122.

W. Hawkes, A. Yasinsac, C. Cline, An Application of Visual Cryptography to Financial Documents, technical report TR001001, Florida State University (2000).

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Nakajima, M. and Yamaguchi, Y., Extended Visual Cryptography for Natural Images, WSCG02 (2002), 303.

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D Chaum, Secret-ballot receipts: True voter-veriable elections, IEEE Security and Privacy (2004), 38-47.

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A.Klein, M. Wessler, Extended Visual Crypotography Schemes, Science Direct (2007), 716-732.

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A. Bonis and A.Santis, Randomness in secret sharing and visual cryptography schemes, Theoretical Comp. Sci. 314 (2004), 351-374.

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