Combining Steganography and Cryptography: New Directions Khalil Challita and Hikmat Farhat Computer Science Department Notre Dame University - Louaize, Lebanon kchallita,hfarhat@ndu.edu.lb Abstract Our main goal in this paper is to give new in- sights and directions on how to improve existing methods of hiding secret messages, possibly by combining steganography and cryptography. We start by describing the main existing methods and techniques in steganography that allow us to hide the existence of a message, together with the mostly used steganalysis techniques to counter them. We then illustrate two different approaches that help us achieve a higher level of secrecy and security, together with their limitations. The first method is about combining steganography and cryptography in such a way to make it harder for a steganalyst to retrieve the plaintext of a secret message from a stego-object if cryptanalysis were not used. The second method does not use any cryptographic techniques at all and relies solely on steganographic ones. Keywords : Steganography, steganalysis, cover object, stego-object, cryptography. 1. Introduction Since the ancient times people have been inter- ested in hiding secret messages. Both cryptogra- phy and steganography achieve this aim, but using different strategies as we next explain. We have stories from the antiquity on how the Greeks received warning of Xerxes hostile in- tentions from a message underneath the wax of a writing tablet; about the use of invisible ink; about ancient Chinese wrote messages on fine silk, which was then crunched into a tiny ball and covered by wax that the messenger swallowed; or about a Roman general who shaved a slaves head and tattooed a message on it. After the hair grew back, the slave was sent to deliver the now-hidden message [13]. Steganography is concerned with sending a se- cret message while hiding its existence. The word steganography is derived from the Greek words steganos, meaning ’covered’, and graphein, meaning ’to write’. On the other hand, cryptography is not concerned with hiding the existence of a message, but rather its meaning by a process called encryption. The word cryptography is derived from the Greek word kryptos, meaning ’hidden’. Several ciphers can be found in the literature such as the Caesar cipher, or the cipher of Mary Queen of Scots that was successfully broken by the lin- guist and cryptanalyst Phelippes, which led to the execution of Mary Queen of Scots in 1587. One may read [27] for more historical notes on the art of exchanging secret messages. A more scientific and formal approach can be found in [26, 21]. Cryptanalysis is the science that tries to defeat cryptography. Many ciphers were shown to be vulnerable to cryptanalytic attacks such as fre- 199 International Journal on New Computer Architectures and Their Applications (IJNCAA) 1(1): 199-208 The Society of Digital Information and Wireless Communications, 2011 (ISSN 2220-9085)