A Secure Keyless Image Steganography Approach for Lossless RGB Images Sankar Roy School of Education Technology Jadavpur University Kolkata, India roy.sankar.ju@gmail.com Ranjan Parekh School of Education Technology Jadavpur University Kolkata, India rparekh@school.jdvu.ac.in ABSTRACT This paper proposes an improved steganography approach for hiding text messages within lossless RGB images. The objective of this work is to increase the security level and to improve the storage capacity while incurring minimal degradation of the image. The security level is increased by distributing the message over the entire image instead of clustering within specific image portions, as also by including a password authentication scheme to ensure that the message can be retrieved only by the intended recipient. Storage capacity is increased by utilizing all the color channels for storing information instead of reserving one of the channels as pixel indicator. Image degradation is minimized by changing only one LSB bit per color channel for hiding the information thereby incurring the least change in the original image. Experimentations done for analyzing the storage capacity and quality degradation, establish the superiority of the proposed approach vis-à-vis contemporary existing approaches. Categories and Subject Descriptors I.4.9 [Computing Methodologies]: Image Processing and Computer Vision —Applications. General Terms Security, Algorithms, Experimentation, Performance Keywords Keyless Steganography, lossless RGB images, authentication 1. INTRODUCTION Steganography is a technique used to transmit a secret message from a sender to a receiver in a way such that a third person does not suspect the existence of the message. Generally this is done by hiding the secret message within another communication medium such as text, image, audio or video. The terms cryptography and steganography are often used synonymously although they are essentially distinct. In cryptography, a plain message is encrypted into ciphertext and might look like a meaningless jumble of characters whereas in case of steganography, the plain message is hidden inside a medium that looks quite normal and does not provide any reason for suspecting the existence of a hidden message. Electronic steganography approaches use digital processing techniques for hiding and detecting embedded information. In case of digital image steganography, the secret message is transmitted embedded within a digital image called a cover image. Once the message is embedded within the image, it is referred to as a stego image. In a keyless steganography approach the sender includes only the hidden information, and does not include any cryptography algorithm or compression. So the reliability and the security is totally dependent on the efficiency of the steganography algorithm itself. In this paper a keyless steganography algorithm applicable for lossless image formats like BMP, PNG or TIF, is proposed. Attempts are made to improve the storage capacity while incurring minimal quality degradation of the image. Security is enhanced by distributing the message throughout the image and by including a password based authentication scheme. The organization of the paper is as follows: section 2, discusses the related works in this area, section 3 describes the proposed algorithm, section 4 provides details about the experimentations and results, and section 5 discusses the overall conclusion and future scopes. 2. LITERATURE REVIEWS Steganography gives a new dimension to the field of secure data communication as it enables one to transmit messages without a potential intruder suspecting its presence. One of the first attempts of steganography includes the least significant bit (LSB) insertion technique where the LSB of a pixel is changed to include a message [1]. For a 24-bit image, 3 bits can be stored in each pixel. To the human eye, the resulting stego image looks almost identical to the cover image. A random LSB insertion method in which secret message is spread out among the image data in a seemingly random manner, can be achieved using a secret key [2]. This is an efficient approach but changes to the MSB bits can degrade the image quality substantially. One of the best keyless steganography approaches is the Pixel Indicator Technique (PIT) algorithm proposed by A. Gutub [3] where he proposes a color channel as pixel indicator and the other two channels as containers of the message. The main drawback is that one of the channels cannot be used to store the actual message. To increase the capacity Stego-1 bit LSB, Stego-2 bit LSB, Stego-3 bit LSB and Stego-4 bit LSB is proposed in [4]. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. ICCCS’11, February 12–14, 2011, Rourkela, Odisha, India. Copyright © 2011 ACM 978-1-4503-0464-1/11/02…$10.00. 573