Java Art Chapter 6. Steganography

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Java Prog. Techniques for Games. Java Art Chapter 6. Stego Draft #1 (7th June 09)Another solution is to keep using LSB, since it's easy to implement, but encrypt themessage before hiding it in the image. A steganalysis tool will still find the hiddenencrypted bits, but they'll look like random data rather a text message.3. The StegCrypt ClassStegCrypt is a modification of the Steganongraphy class which encrypts the binaryversion of the plain-text message before hiding it in an image.The byte array encryption and decryption is done using Jasypt'sBasicBinaryEncryptor class. Jasypt (http://www.jasypt.org/) lets a programmeremploy basic encryption capabilities without requiring a deep knowledge ofcryptography.Jasypt doesn't implement any encryption algorithms itself, but acts as a simplifyinginterface to the JCE (Java Cryptography Extension), an API that provides securityfeatures via the JVM (or third party providers such as Bouncy Castle(http://www.bouncycastle.org/)).A fundamental question with encryption is how to safely send the encryptedmessage's password (or key) to the message's recipient. I 'solve' this problem byincluding the password as part of the stego message, which now has three fields:This approach is fine since the aim of the encryption is only to scramble the messageso that a basic LSB steganalysis attack will not reveal plain-text. Of course, if theattacker knows that the first field is the message's password, then the original messagecan be retrieved.The password is a 10-letter randomly generated string, which will be stored in 10*8bytes in the image. The message size is a Java integer (i.e. 4 bytes long), whichutilizes 4*8 bytes in the image. Each byte of the encrypted message needs 8 bytes ofstorage in the image.The StegCrypt class has the same public interface as Steganongraphy, two publicstatic methods:boolean hide(String textFnm, String imFnm);boolean reveal(String imFnm);3.1. Hiding a Messagehide() loads the text and image, and saves the modified image in the same way as theSteganography class. The differences come in the use of a password to encrypt thetext:public static boolean hide(String textFnm, String imFnm)/* hide message read from textFnm inside image read from imFnm;12 Andrew Davison © 2009
Java Prog. Techniques for Games. Java Art Chapter 6. Stego Draft #1 (7th June 09){the resulting image is stored in Msg.png */// read in the message as a byte arraybyte[] msgBytes = readMsgBytes(textFnm);if (msgBytes == null)return false;// generate a passwordString password = genPassword();byte[] passBytes = password.getBytes();// use password to encrypt the messagebyte[] encryptedMsgBytes = encryptMsgBytes(msgBytes, password);if (encryptedMsgBytes == null)return false;byte[] stego = buildStego(passBytes, encryptedMsgBytes);// access the image's data as a byte arrayBufferedImage im = loadImage(imFnm);if (im == null)return false;byte imBytes[] = accessBytes(im);if (!singleHide(imBytes, stego))return false;// im is modified with the stego// store the modified image in Msg.pngString fnm = getFileName(imFnm);return writeImageToFile( fnm + "Msg.png", im);} // end of hide()One benefit of staying with LSB hiding, is that once the byte array holding the threepartstego message has been constructed (i.e. the stego[] array is filled), then the samesingleHide() method as in Steganongraphy can be employed to write it into theimage's data.genPassword() generates a 10-letter random string.// globalsprivate static final int PASSWORD_LEN = 10;private static Random rand = new Random(); //used for passwd genprivate static String genPassword(){String availChars ="abcdefghjklmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ23456789";// chars available for passwordStringBuffer sb = new StringBuffer(PASSWORD_LEN);for (int i=0; i
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Java Art Chapter 6. Steganography

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