Rayan Ghamri



Rayan Ghamri100837786LSB based SteganographyAdvanced security design CS 691Semester ProjectDr.Edward ChowUnivsersity of Colorado at Colorado Springs. Summer 2011OverviewFrom time immemorial, people organized the need to pass the information from one person to another while keeping that information unknown or as a secret to enemies. Since then there was a need for the information to be secured and hidden. And that what is securing all about.Today there are computers and Internet, which means there is information and it needs to be transmitted from one person to another but without getting stolen or reviled. When we want to send some information to a person we use cryptography so the message always encrypted and when it gets to the receiver it gets decrypted. It’s a simple idea but too hard to implement. Also, sometimes when someone gets the ciphertext they might get the plaintext after trying so hard to get it. But what if we had used something no one can detect something we always send to each other’s. Something will not attract any attention, such as an image, video or even a song by The Beatles. This was the beginning of Steganography.DefinitionSteganography comes from the Greek words Steganós (Covered) and Graptos (Writing). Steganography in these days refers to information or a file that has been concealed inside a digital picture, video or audio file. If a person or persons view the object that the information is hidden inside, he or she will have no idea that there is any hidden information; therefore the person will not attempt to decrypt the information.Steganographic TechniquesPhysical SteganographyPhysical Steganography is the first real use of Steganography and it has been widely used in ancient times. For examples: people wrote message on wood and then covered it with wax. Message was written on the back of postage stamps. Message was written on paper by secret inks. Also shaved the head of his most trusted slave and tattooed a message on it. After his hair had grown the message was hidden, this was used back on 440BC.Printed SteganographyThe letter size, spacing and other characteristics of a cover text can be manipulated to carry the hidden message. A recipient who knows the technique used can recover the message and then decrypt it. For example:These messages were sent by the German embassy in WorldWar I. This is called a null cipher. First litterPRESIDENT'S EMBARGO RULING SHOULD HAVE IMMEDIATE NOTICE. GRAVE SITUATION AFFECTING INTERNATIONAL LAW. STATEMENT FORESHADOWS RUIN OF MANY NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT IMMENSELY.The second letterOF MANY NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT IMMENSELY. APPARENTLY NEUTRAL'S PROTEST IS THOROUGHLY DISCOUNTED AND IGNORED. ISMAN HARD HIT. BLOCKADE ISSUE AFFECTS PRETEXT FOR EMBARGO ON BYPRODUCTS, EJECTING SUETS AND VEGETABLE OILS.¤ Taking the first letter in each word of message 1 or second letter in message 2 reveals the hidden text. PERSHING SAILS FROM NY JUNE 1.Digital SteganographyDigital Steganography is today’s Steganography and it can be wildly used because it uses the concept of invisibly hiding data within data. It conceals the fact that message exists by hiding the actual message. In this, secret data can be hidden inside the image, text, sound clip that can be represented in binary. Why steganography?Steganography can provide a reliable, flexible and user friendly alternative to encryption and can be used in countries where cryptography is prohibited. Alternative to CryptographyFor sure there will be a malicious intervention as long as there are electrical communication. Cryptography helped to fight this intervention and gives security and confidentiality to the existing message and the outcome will be an encrypted message. That message will have it’s own authentication code appended so that recipients must prove their integrity and authenticity before unencryption occurs.With steganography, the message, whether encrypted or not, is hidden in images and invisible to unauthorised recipients, or at least hard to detect. It is a new science that provides added security, privacy and confidentiality when used instead of or in conjunction with cryptography.Steganography SystemA steganographic system is composed of an encoder and a corresponding decoder, as shown in Figure below. The encoder has three inputs. One is the payload we want to embed, one is the stego key, the aim of which is to protect the carrier image so that after encoding, unauthorized or malicious users cannot decode it, and the third is the cover image in which payload will be embedded. The output of the encoder is the stego image, which may be transmitted or recorded and will be the input to the decoder. The encoder sends the stego key to the decoder to allow visibility of the payload.Steganography Vs CryptographyCryptography is the science of scrambling a message by using algorithms to convert the secret data into an incomprehensible form. Steganography hides the message, still in a comprehensible form, so that it cannot be seen. The unauthorized recipient of an encrypted message knows that secret information exists, while unlike a steganographic message, whose very existence is unsuspected.SteganographyCryptographySecurity in SteganographySteganography is an efficient way to hiding data, protecting the data from unauthorized access or viewing. Some steganographic approaches are too simple, however, such as pure LSB hiding, as hidden data can be detected with ease Steganography Detection in LSBThe commonest way to hide data is to embed it in an image by replacing the least significant bits (LSB) of red, green and blue components in the pixels of a 24-bit image. That anything has been embedded is difficult to detect visually as the human eye cannot discriminate the difference in pixels. LSB methods cannot, however, resist extraction or attacks like compression and cropping.Least Significant Bit Technique (LSB)In Least Significant Bit technique (LSB) steganography encoding occurs in spatial or image domain not in frequency domain. Then in spatial domain various steps are involved and are discussed in next section.LSB Encoding Algorithm LSB Encoding AlgorithmInput: secret message, stego key, original imageProcedure:Step1. Convert original image to color bytes (no alpha byte)Step2. Step3. while complete message not embedded do 3.1 get next color byte 3.2.1 get next bit from message 3.2.2 replace color byte LSB with message bit end{while}Step4. Convert color bytes to stego imageEnd.Output: stego imageLSB Encoding ProcessThis process consists of following stepsStep 1:In step 1 first image is converted to pixels. Then these pixels split to R, G and B bytes. These bytes are stored in array. These will be further processed in next steps.Step 2:In this step secret message is converted to bytes.Step 3:In this step actual data hiding occurs. Each bit of secret message is inserted to least significant bit of color byte. So one byte of message is inserted in 8 color bytes. By using this formulaN color bytes = N *1/8 message bytesThe process of inserting message bits to least significant bit of color byte repeats until all messages are completed.In order to understand how color bytes looks after modification we have to consider example. Let we have message byte and we want that byte to insert it in color bytes, message byte isM = 0110 0010M consists of 8 bits so it will require 8 bytes of color bytes. Let we have 9 color bytes and before encoding process these bytes looks likeRGB001011010001110011011100101001101100010000001100110100101010110101100011Before LSB EncodingAfter LSB encoding we see from Table that least significant bit of color bytes are changed indicated by bold letters. These bold bits are M message bits RGB001011000001110111011101101001101100010000001100110100111010110001100011 After LSB EencodingThis process repeats until the entire secret message bits are inserted in least significant bit of color bytes.Step 4:In this step the modified color bytes are combined to pixels and are converted back to image. Output of this process is stego image. LSB Decoding AlgorithmInput: stego image, stego keyStep1. Convert stego image to color bytes (no alpha byte)Step2. Step3. while complete message length do 3.1 get next color byte 3.2.1 concatenate color byte LSB to secret message end{while}Step4. Decode secret message and show output End.Output: secret message LSB decoding algorithmLSB Decoding ProcessStep 1:In step 1 first image is converted to pixels. Then these pixels split to R, G and B bytes. These bytes are stored in array. There will be further processed in next steps.Step 2:In this step actual extraction occurs. Here have color bytes, now in order to create message least significant bit of these bytes are extracted and then they are concatenated to create secret message. Concatenation occurs in length of 8 bits (1 byte). Eight bits are extracted and then they are concatenated to produce byte. This process repeats until the entire secret message completes. In order to understand how decoding works consider example. In this example we have 9 color bytes in the table we see bold letter these are message bytes that are inserted in Encoding phase. RGB001011000001110111011101101001101100010000001100110100111010110001100011 Encoded bytesLeast significant bit of each color byte is extracted and then concatenated to produce M message byte M = 0110 0010. This process repeats until all the message bytes are extracted.Step 3:In this step all extracted bytes are converted to secret message and presented to user. LSB Decoding AlgorithmHow invisibility achievedAfter encoding step user cannot visually detect that something is hidden in stego image. Since bytes values are changed if least significant bit changes. We see from Table byte values are changed when LSB implemented but in color column we see that visually before and after encoding colors are almost same. That’s why user cannot see any difference in original and stego image. RGB value in bitsRGB value in bytesColorBefore Encoding00101101, 00011100, 1101110045, 28, 22010100110, 11000100, 00001100166, 196, 1211010010, 10101101, 01100011210, 173, 99After Encoding00101100, 00011101, 1101110144, 29, 22110100110, 11000100, 00001100166, 196, 1211010011, 10101100, 01100011211, 172, 99Compression of before and after encoding valuesExperimental ResultsFrom these two pictures we cannot find any difference visually but there is hidden secret message.Image before LSB EncodingImage after LSB EncodingAdvantagesThis algorithm provides high hiding capacity.Simple algorithm and simple to understand.It takes less time to encode secret message.DisadvantagesBy using steganalysis technique it will be easy to detect hidden message.It is fragile technique. References[1] Wikipedia [2] Ekta Walia, Payal jain, Naveep, “ An Analysis of LSB & DTC based Sreganography.” P.4 Global journal of computer science and technology. April 2010.[3] Alaa O. Khadidos “DISTRIBUTED STEGANOGRAPHY FILE SYSTEMS” University of Birmingham [4] Michael T. Raggo, CISSP Principal Security Consultant VeriSign “Steganography, Steganalysis, & Cryptanalysis”[5] Brian Mearns, “Least-Significant Bit Steganography and Steganalysis”[6] Java territorial in steganography ................
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