ISBN: 978 – 81 – 922119 – 4–7 1 Proceedings of the “National Conference on Emerging Trends in Information and Computing Technologies” (NCETICT-2012), 30 th March, 2012. A Novel Steganographic Technique Based on LSB-DCT Approach Mohit Kumar Goel Department of Electronics & Electrical Comm. Engineering PEC University of Technology Chandigarh, India mohitgoel4u@gmail.com Neelu Jain Department of Electronics & Electrical Comm. Engineering PEC University of Technology Chandigarh, India neelujain@pec.ac.in Abstract —Steganography is the art of concealing data within other digital media like an image or an audio signal for providing higher security. The security includes both imperceptibility and undetectability. But most of the steganographic methods don’t pay enough attention to the undetectability. In this paper, we propose a novel DCT-based steganographic method for hiding the data. Each bit of data is embedded by altering the least significant bit of low frequency DCT coefficients of cover image blocks. The experimental results show that this algorithm has better PSNR value and high capacity in comparison to other techniques such as LSB, modulus arithmetic, SSB4-DCT. It also maintains satisfactory security as secret message cannot be extracted without knowing the decoding algorithm. Keywords: Steganography; Discrete Cosine Transform; Zigzag scanning; Data hiding. I. INTRODUCTION With the development of science, digital media can be transmitted conveniently over the internet. The security of the data is essential issue for the internet. Encryption is introduced for the data security. Encryption scrambles the secret message so that it cannot be understood. But, it makes the message suspicious enough to attract eavesdropper‘s attention. The commonly used encryption schemes include DES (Data Encryption Standard) [1], AES (Advanced Encryption Standard) [2] and RSA [3]. After encryption watermarking is introduced. In watermarking technique the owner property is protected by some hidden watermarks. A new scheme, called ―steganography‖ [4], is proposed to conceal the secret messages within some image, music or audio file so that it is not visible to others. Steganography differs from cryptography in the sense that where cryptography focuses on concealing the contents of a message, steganography focuses on concealing the existence of a message [5]. The word steganography in Greek means ―covered writing‖ (Greek words ―stegos‖ meaning ―cover‖ and ―grafia‖ meaning ―writing‖). Steganography is the art and science of hiding information in a cover document such as digital images in a way that conceals the existence of hidden data. The main objective of steganography is to communicate securely in such a way that the true message is not visible to the intruder. Image steganography schemes can be divided into two categories: Spatial Domain and Frequency Domain. A. Spatial domain steganography Spatial domain techniques embed messages in the intensity of the pixels directly [6][7][8]. Least Significant Bit (LSB) is the first most widely used spatial domain steganography technique. It embeds the bits of a message in the LSB of the image pixels [9][10]. But the problem with this technique is that if the image is compressed then the embedded data may be lost. Thus, there is a fear for loss of data that may have sensitive information [11]. LSB has been improved by using a Pseudo Random Number Generator (PRNG) and a secret key in order to have private access to the embedded information [12]. The embedding process starts with deriving a seed for a PRNG from the user password and generating a random walk through the cover image that makes the steganalysis hard. Another recent improvement based on random distribution of the message was introduced by M. Bani Younes and A. Jantan [13]. In this method they utilize an encryption key to hide information about horizontal and vertical blocks where the secret message bits are randomly concealed. SSB-4 steganography approach introduced by Rodrigues, Rios and Puech is about changing the 4 th bit of a pixel in the original image according to the bit message. Then modify the other bits (1 st , 2 nd , 3 rd and/or 5 th ) to minimize the difference between the changed pixel value and the original one [14]. The 4 th digit is a significant bit and if the image is compressed the embedded information is not destroyed [15]. Tu C. and Tran T D. argued that the difference must be equal or less than four (i.e., ±4) [16]. The 4 th bit was chosen because it satisfies that changing of ±4 units in the channel color value is imperceptible to human eyes, and it is the most significant bit which provides the minimum change in the pixel values. Modulus arithmetic steganography proposed by Sayuthi Jaafar and Azizah A Manaf has calculated last four bits of each pixel by mod-16 operation. Then these bits are replaced with data bits [8]. In this the amount of the data that can be embedded is more but stego image has less PSNR value than LSB and SSB-4 techniques. B. Frequency domain steganography In frequency domain, images are first transformed and then the message is embedded in the image [17][18][19]. When the data is embedded in frequency domain, the hidden data resides