VLSI Realization of a Secure Cryptosystemand Steganography in ImageEncryption and Decryption by VANMATHI.R

&

PRABAVATHI.M

BE(ECE)

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Abstract

In this paper I present a technique that allows cryptography to inherit some features from steganography in such a way that the information is encrypted as well as hidden. The proposed solution is to use image cryptography to hide textual data. The process is to transfer encrypted textual data but in image format..

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Literature Survey Image Steganography Methods

– Replacing Least Significant Bit: The Embedding data is hidden by replacing the least significant bit (LSB) of each pixel in the cover image

– Replacing Moderate Significant Bit: The Embedding data is hidden by replacing the moderate significant bit (MSB) of each pixel in the cover image

– Transformation Domain Techniques: Other familiar data hiding techniques use the transformation domain of digital media to hide information. These methods hide the messages in the significant areas of the cover image which makes them robust against compression, cropping and other image processing attacks

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Cryptography In Cryptography, the meaning of the message is

hidden, not its existence– Kryptos = “hidden” in Greek– Cryptography is the fundamental technique to counter

these threats because the outsider does not understand the meaning of messages

Cryptanalyst: Person working for unauthorized interceptor

Cryptographer: Person working for legitimate sender or receiver

Cryptology: Study of encryption and decryption, including cryptography and cryptanalysis

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Modern Encryption Principles An encryption scheme has 5 ingredients

– Plaintext, Encryption Algorithm, Key, Ciphertext, and Decryption Algorithm

– Security depends on secrecy of the key, not algorithm

Proposed Conceptual Framework

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Selection of image area for hiding textual data In this step we propose to insert the secret text on

the selected image. We have two basic assumptions in this step: – firstly, the sender and the receiver know which image is

being transmitted and – secondly, the area in the image that is used for hiding

secret data. Selecting a proper portion in the image is a very essential step because we are going to modify the pixels in the spatial domain. After selecting a proper portion in an image the text can be inserted.

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Information hiding by modifying image within the Spatial Domain In this step i propose to use: Replacing Least Significant Bit: The Embedding data is

hidden by replacing the least significant bit (LSB) of each pixel in the cover image

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Advanced Encryption Standard (AES) The Advanced Encryption Standard (AES) specifies a

approved cryptographic algorithm that can be used to protect electronic data.

The AES algorithm is a symmetric block cipher that can encrypt (encipher) and decrypt (decipher) information.

Encryption converts data to an unintelligible form called ciphertext.

Decrypting the ciphertext converts the data back into its original form, called plaintext.

The AES algorithm is capable of using cryptographic keys of 128, 192, and 256 bits to encrypt and decrypt data in blocks of 128

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There a four basic step, called layers, that are used to form the rounds:

(1) The ByteSub (SB) Transformation: This non-linear layer is for resistance to differential and linear cryptanalysis attacks.

(2) The ShiftRow (SR) Transformation: This linear mixing step causes diffusion of the bits over multiple rounds.

(3) The MixColumn (MC) Transformation: This layer has a purpose similar to ShiftRow.

(4) AddRoundKey (ARK) Transformation: The round key is XORed with the result of the above layer.

Decryption

Each of the steps Byte Sub, Shift Row, Mix Column, and AddRoundKey is inversible:

(1) The inverse of Byte Sub is another lookup table, called InvByteSub (IBS).

(2) The inverse of Shift Row is obtained by shifting the rows to the right instead of to the left, yielding InvShiftRow (ISR)

(3) The transformation InvMixColumn (IMC) is given by multiplication by the matrix

(4) AddRoundKey is its own inverse.

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AES Encryption Algorithm Flow

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Basics of Modern SteganographySteganography

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fE:     steganographic function "embedding"fE-1:   steganographic function "extracting"cover:  cover data in which emb will be hiddenemb:    message to be hiddenkey:    parameter of fEstego:  cover data with the hidden message

Steganalysis meets Cryptanalysis Knowing the steganography program used to

hide the message can be extremely handy when attempting to reveal the actual hidden message

Identifying and cracking the algorithm– Unfortunately, some of these programs use

strong encryption 256-bit or stronger Reveal or Crack the password, seed, or secret

key– Practically all Steganography programs use

a password to hide the message

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Steganalysis meets Cryptanalysis

Cryptanalysis As stated previously, in

Steganography the goal is to hide the message, NOT encrypt it

Cryptography provides the means to encrypt the message

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Steganography – Modern Day

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Anomaly – Visual Detection

Can you see a difference in these two pictures?

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Result Analysis

If the encrption and decryption key is wrong,then the output of hidden text will be a display unknown text.

To view original hidden message, keys or password should be loaded correctly in both encryption and decryption sides.

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If the key or password loaded is wrong then the output of the decrypted emmbedded text will be wrong as follows in below simulation analysis..

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Conclusion In this paper i proposed a new technique of

using image as a cover medium for concealing cryptographic communication.

This is a new technique, which can be used to disguise the use of encrypted communication as well as keep the hidden information secret

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