1. Information Hiding Cryptography & Steganography
Lesson 6

2. What is Cryptography
Protecting information by transforming it into an unreadable format
Encryption is the process that transforms the data into the unreadable format, Decryption restores it to its original format.
Used to prevent information from “falling into the wrong hands”
Data is only available to the people that are supposed to see it

3. A little history Cryptography is not new 1900 BC hieroglyphics
60 BC Caesar cipher
Simple substitution cipher
Replace each letter with alphabet shifted K letters
If K=3 then “hello” becomes “khoor”
Thomas Jefferson considered by some to be the father of U.S. cryptography
Cryptography vital during World Wars
German Enigma machine in WW II
“Lucifer” IBM project in late 1960’s became successful commercial product

4. How does it work A few terms Plaintext – the original message
Ciphertext – the encrypted message
Encryption – how the message is scrambled
Decryption – how the message is unscrambled
Cryptographic system – specific method of encryption and decryption (also called a cipher or cryptosystem)
Transposition – rearranging elements
Substitution – replacing elements

5. How does it work Encryption is NOT the same as a code
Code – words are substituted for other words
Navajo code talkers from WW II
“dah-he-tih-hi (hummingbird) substituted for “fighter plane”
“besh-lo” (iron fish) meant “submarine”

6. How does it work Encryptkey(Plaintext) = Ciphertext
Decryptkey(Ciphertext) = Plaintext
Must know method and key (if used)
Not all crypto methods use keys

7. How does it work Caesar cipher
Plaintext = “hello”
Encryption method = substitute letter with letter plus 3
Encrypt(“hello”) = Ciphertext = “khoor”
How can we make this method more secure?

8. How does it work Caesar cipher with incrementing substitution
Plaintext = “hello”
Encryption method = substitute letter with letter(I) where I starts at 3 and increments 1 for each letter
Encrypt(“hello”) = Ciphertext = “kiqrv”

9. Different Methods
Symmetric – same key is used for both encryption and decryption (also called private key encryption)
DES - Data Encryption Standard
Loosely based on Lucifer which used 112 bit keys
NSA asked that the key length be shortened to 56 bits
Triple-DES – variant of DES
AES - Advanced Encryption Standard
IDEA – International Data Encryption Algorithm

10. Different Methods DES Encrypts 64-bit blocks using a 56-bit key
64-bit block is permutated
64-bit block split into two 32-bit blocks
Each sub-block is combined with the key and processed 16 times
Sub-blocks are joined and sent through an inverse permutation process

11. How DES Works Initial Permutation DES operates on a 64-bit block of
plaintext which it
breaks into two
32 bit blocks.

12. Different Methods Skipjack – developed and released by NSA
Uses 80-bit keys
Used in Clipper chip
Meant to help FBI combat criminals using encryption
Built in back door for law enforcement
Government has “master key”
Key escrow – session key held for later release to law enforcement when needed
Government tried to force this as a standard
Not widely accepted

13. Different Methods Problems with symmetric methods
Same key is used to encrypt and decrypt
Shared key is more likely to be compromised
Possible to brute force short keys
Certain keys are weak
Different keys can produce identical ciphertext
Distribution of keys

14. Different Methods
Asymmetric – uses two different keys (also called public key)
Private key – known only to one party
Public key – available to anyone
Diffie-Hellman
First discussion of public-key distribution system
RSA (named for its inventors Ron Rivest, Adi Shamir, and Leonard Adleman)
PGP (Pretty Good Privacy)

15. Different Methods Diffie-Hellman Method
Ciphertext = Encrypt public key[Plaintext]
Plaintext = Decrypt private key[Ciphertext]
Each party creates their own private key
Each party computes a public key using a mathematical function of the private key
Public keys are exchanged
Message key is computed from other person’s public key and your own private key
If the math is right, the message key is the same on both sides

16. Uses of Public Key Cryptography
Digital Signatures
Used to authenticate digital material
Prove identity and validity of action or material
Transmission of symmetric key (public key encryption is generally slower)

17. Uses of Public Key Cryptography
Digital Signatures and Public Key Encryption
Message encrypted or signed with private key of sender and public key of recipient
Recipient decrypts with own private key and sender’s public key
Only sender has the right private key so if it decrypts it must have come from the sender
NOTE: Assumes keys have not been compromised

18. Uses of Cryptography Digital Certificates
Used to encode and verify messages
Requires a Certificate Authority that creates a digital certificate based on a private key and other authentication information
Implements the “trusted third party” concept
X.509 is a popular standard for defining digital certificates

19. Uses of Cryptography VPN (Virtual Private Network)
Connects geographically separate offices using public communication means
Packets are usually “tunneled” – entire packet is encrypted and encapsulated in a new packet before sending
Hardware or software based
Sometimes integrated into firewalls
Usually cheaper than leased lines
Very good for mobile employees that need access to the company network

20. Uses of Cryptography Smart Cards
IPv6 will support IPsec – built in encryption
SSH – Secure Shell, an alternative to Telnet
– PGP very popular in this area
File or disk encryption

21. Uses of Cryptography Key Escrow and Key Recovery
Keys held in “reserve” in case the original keys are lost or damaged
Usually split between two parties, each with half of the key
Often requires two or more people to access and recover key

22. Breaking Crypto Weaknesses The human factor
Security of key and message
Key length
Short keys can be broken even with a good algorithm
Algorithm
Very difficult to develop a secure algorithm
Weak algorithm can be insecure even with a long key

23. Breaking Crypto Differential Cryptanalysis Linear Cryptanalysis
Look for differences in pairs of messages
Only works on certain ciphers
Linear Cryptanalysis
Looks for simple approximation of encryption function
Differential Power Analysis
Measures power consumption of hardware encryption devices
The basic idea of the attacks is that the power consumption of a
device (such as a smartcard) is statistically correlated to the
operations it performs. By monitoring the power usage (or
electromagnetic radiation, etc.) during cryptographic operations, it
is possible to obtain information correlated to the keys. The
collected data is then analyzed to actually find the keys.

24. DPA

25. Breaking Crypto Brute Force DES Challenge
Just try different keys until you get one that works
DES Challenge
Worked off of 56 bit keys
Sponsored by RSA to show weaknesses in DES
Electronic Frontier Foundation built special system (DES Cracker) to crack DES in 56 hours
Jan 19, 1999 – Distributed.Net cracks 56-bit DES in 22 hours and 15 minutes using 100,000 PCs on Internet and DES Cracker
Testing 245 billion keys per second
Depends on where key falls in possible keyspace

26. Breaking Crypto
Advances in computing power enhances ability to break crypto.
56-bit DES broken in less than a day
Roughly 70 thousand trillion possible keys
128-bit DES would have 3 * 10^38 possible keys
1 billion processors capable of processing 100 million keys/sec would take 10^20 years to try all keys
Cracking just needs to find a suitable key, not try every combination

27. Steganography

28. Steganography Literally means “covered writing”
The practice of hiding a message in such a manner that its very existence is concealed.
Done by embedding the message in some medium such as a document, image, sound recording, or video.
Those who know the medium contains a message can extract it.
For those who don’t know about it, the message will be completely invisible.
Related concept is digital “watermarking”

29. Steganography -- historical examples
In the Histories of Herodotus
Demaratus wanted to notify the Spartans that Xerxes planned to invade Greece. He had the wax scraped off of writing tablets, the message carved into the wood, then recovered with the wax. The message was thus hidden.
Shave the head of a messenger, tattoo the message on his head, let his hair grow back.
Codes, invisible ink, microdots

30. Encoded messages “Pershing sails from N.Y. June 1”
Example 1: President’s embargo ruling should have immediate notice. Grave situation affecting international law, statement foreshadows ruin of many neutrals. Yellow journals unifying national excitement immensely.
Example 2: 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.

31. Hiding images in files Takes advantage of coding scheme
For pictures, each pixel represented by 1 or more bytes.
If the least significant bit is used to encode the message, small variations in the picture may occur but the message will be hidden inside.
A 400 x 300 image will have 120,000 pixels thus
if 8 bit coding scheme (256 colors) 120,000 bits of coded message can be encrypted or 15,000 bytes (characters).
If RGB scheme used with 3 bytes/pixel (one for each color RGB) even more data can be hidden since the resulting file is much larger.

32. Steganography
CAB =
8 shades of gray
000
001
010
011
100
101
110
111

33. Steganography
CAB =
Original =
Hidden =
8 shades of gray
000
001
010
011
100
101
110
111

34. Steganography original hidden original 8 shades of gray 000 001 010
original
hidden
original
8 shades of gray
000
001
010
011
100
101
110
111

35. Example (hideseek on gif file)
Original
Version with hidden text
Text: “This is a MacGregor 26X.”

36. Example (hideseek on gif file)
Original
Version with hidden text
Text: “This is a MacGregor 26X under power.
Cool looking boat with lots of neat features.
Uses water ballast system so very easily trailered.
This also results in an extremely shallow draft so
it can be easily beached..”

37. Example (PGE on jpg file)
Original
Picture with hidden text
Text: “A sample text to hide.”

38. Example (PGE on jpg file)
Original
Picture with hidden text
Text: “A sample text to hide.
This is a larger file to hide.
The photo is cool, how did that car get
underneath the jet in the first place?”

39. Example (Hide4pgp with wav)
Original
Wav file with hidden text
Text: “An example of text hidden in a sound file.”

40. Steganography (TextHide)

41. Steganography (TextHide)

42. What can you do about it? First of all, why worry? Detection
There are some legitimate concerns but often there are many other easy ways to conceal/capture info.
Detection
Watermarks harder than complete stego images
Any manipulation of image introduces distortion
Changes between colors rarely occur in 1-bit shifts
(not true of gray-scale)
one way to foil is to use color palettes that change dramatically with 1-bit shifts