1. CSCI 530L Steganography and Steganalysis

2. Administrative issues If you have not yet signed up for a Lab Section, do so now. Most lab sections are full Send an e-mail to csci530l@usc.edu with the exact subject line “Lab Time Request”csci530l@usc.edu List the lab sections 1-7 in order of preference

3. Any Difference?

4. Steganography Introduction Steganography The art and science of hiding information by embedding messages within other seemingly harmless messages in such a way that no one besides the intended recipient is able to retrieve it. It is different than Cryptography Cryptography in a broad sense means scrambling of data using a particular algorithm Steganography is about hiding data

5. Hiding Data Steganography – hiding a file inside of another Typically hiding text inside of a media file Normally used for the transportation of secretive information Operating System Unused memory Slack space Unallocated space Hidden partition Normally used to hide data from investigators Network Unused bits in packet headers

6. Steganography Applications Terrorist and Criminal Activities “Terrorist instructions hidden online “  U.S. News “Messages in dots”  U.S.News Corporate Espionage Trading company secretss

7. Steganography Approaches Chaffing and Winnowing Ron Rivest Bob sends multiple messages to Alice, but only one is authenticated. The rest are bogus. Eavesdropper cannot determine which are real and which are fake Least Significant Bit Manipulation

8. Least Signifiacant Bit Manupalation Idea is that the least significant bit of a byte can change with little change to the overall file Consider a 8-bit grey scale image One pixel of information is stored using 8 bits. There are 256 different variations of grey. 1 0 0 1 0 1 1 0 MSBLSB

9. LSB continued Change in the LSB information of some area of the image will not be noticeable by naked eye. Utilizing this fact the message is embedded 10101101 00101010 10100010 10010001 10… 10101100 00101011 10100011 10010000 10…

10. LSB advantages and disadvantages Advantages Does not change the size of the file Is harder to detect than other steganography techniques Disadvantages Normally must use the original program to hide and reveal data If the picture with the hidden information is converted to another format, then the hidden data may be lost