A New Method of Coding for Steganography Based on LSB Matching Revisited
Mansoor Fateh, Mohsen Rezvani, Yasser Irani
Abstract
LSB matching revisited is an LSB-based approach for image steganography. This method is a type of coding to increase the capacity of steganography. In this method, two bits of the secret message are hidden in two pixels with only one change. But this method provides no idea for hiding a message with a large number of bits. In other words, this method works only for <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" id="M1"> <a:mi>n</a:mi> <a:mo>=</a:mo> <a:mn>2</a:mn> </a:math> , where <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" id="M2"> <c:mi>n</c:mi> </c:math> is the number of bits in a block of the secret message. In this paper, we propose an improved version of the LSB matching revisited approach, which works for <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" id="M3"> <e:mi>n</e:mi> <e:mo>></e:mo> <e:mn>2</e:mn> </e:math> . The proposed scheme contains two phases including embedding and extracting the message. In the embedding phase, we first convert the secret message into a bit-stream, and then the bit-stream is divided into a set of blocks including <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" id="M4"> <g:mi>n</g:mi> </g:math> bits in each block. Then we choose <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" id="M5"> <i:msup> <i:mrow> <i:mn>2</i:mn> </i:mrow> <i:mrow> <i:mi>n</i:mi> <i:mo>−</i:mo> <i:mn>1</i:mn> </i:mrow> </i:msup> </i:math> pixels for hiding such <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" id="M6"> <k:mi>n</k:mi> </k:math> bits of the secret message. In the next step, we choose the operations needed to generate such a message. Finally, we perform the obtained operations over the coefficients to hide the secret message. The proposed approach needs fewer changes than LSB MR when <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" id="M7"> <m:mi>n</m:mi> <m:mo>></m:mo> <m:mn>2</m:mn> </m:math> . The capacity of the proposed approach is <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" id="M8"> <o:mfenced open="(" close=")" separators="|"> <o:mrow> <o:mfenced open="(" close=")" separators="|"> <o:mrow> <o:mfenced open="(" close=")" separators="|"> <o:mrow> <o:msup> <o:mrow> <o:mn>2</o:mn> </o:mrow> <o:mrow> <o:mi>n</o:mi> </o:mrow> </o:msup> <o:mo>−</o:mo> <o:mn>1</o:mn> </o:mrow> </o:mfenced> <o:mo>/</o:mo> <o:mrow> <o:msup> <o:mrow> <o:mn>2</o:mn> </o:mrow> <o:mrow> <o:mi>n</o:mi> <o:mo>−</o:mo> <o:mn>1</o:mn> </o:mrow> </o:msup> </o:mrow> </o:mrow> </o:mfenced> <o:mo>−</o:mo> <o:mn>1</o:mn> </o:mrow> </o:mfenced> <o:mo>×</o:mo> <o:mn>100</o:mn> <o:mo>%</o:mo> </o:math> higher than the F5 method where this value for <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" id="M9"> <z:mi>n</z:mi> <z:mo>></z:mo> <z:mn>2</z:mn> </z:math> is bigger than 75%. For example, the capacity of our scheme is 75% higher than the capacity of F5 for <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML" id="M10"> <bb:mi>n</bb:mi> <bb:mo>=</bb:mo> <bb:mn>3</bb:mn> </bb:math> . The proposed method can be used in the first step of every steganography method to reduce the change in the stego image. Therefore, this method is a new coding method for steganography. Our experimental results using steganalysis show that using our method provides around 10% higher detection error for SRNet over two steganography schemes.