SCSC 455 Computer Security
Chapter 2 Symmetric Encryption and
Message Confidentiality
Dr. Frank Li
Index

Symmetric encryption principles

Symmetric block encryption

Random and pseudorandom numbers

Stream ciphers and RC4
Cipher block modes of operation

Symmetric encryption principles

Five ingredients:





Plaintext
Encryption algorithm
Secret key
Cipher text
Decryption algorithm
Kerckhoff’s Principle

Kerckhoff’s Principle (1883)

the only secrecy involved with a cryptography system
should be the key; the algorithm should be publicly
known;

Good security assumes an eavesdropper knows the
cipher, but the key must be kept secret
Cryptography

Cryptographic systems are classified along three
independent dimensions:

The type of operations used for transforming



The number of keys used


Substitution vs. transposition
Product systems
Symmetric vs. asymmetric
The way in which the plaintext is processed

Block cipher vs. stream cipher
Cryptanalysis


The process of attempting to discover the plaintext
or key
Types of cryptanalytic attacks (table 2.1)





Cipher text only
Known plaintext
Chosen plaintext
Chosen ciphertext
Chosen text
Computationally Secure

A encryption scheme is computationally secure, if
the ciphertext generated by the scheme meets one
or both of criteria:



The cost …
The time …
Brute force attack

X different keys  on average ? Tries
Feistel Cipher Structure


Many symmetric block encryption algorithms have a
structure … (figure 2.2)
Feistel Structure is a particular example of the more
general structure used by all symmetric block
ciphers

Parameters and design features







Block size
Key size
Number of rounds
Subkey generation algorithm
Round function
Fast software encryption/decryption
Ease of analysis
Symmetric block encryption algorithms

important symmetric block ciphers



DES
3DES
AES
DES

Data encryption standard




Issued in1977 FIPS 46 by NIST
The algorithm is Data encryption algorithm (DEA)
What is DES?
The strength of DES


Concerns about the algorithm …
Concerns about key length …
History of DES (1)

In the early 1970s, the National Institute of Standards and
Technology (NIST) invited vendors to submit data encryption
algorithms to be used as a cryptographic standard.

In 1974, IBM’s 128-bit algorithm Lucifer was submitted and
accepted.

The NSA modified Lucifer to use a key size of 64 bits instead of
the original 128 bits, and named it the Data Encryption Algorithm
(DEA).

DEA became the algorithm that fulfills the Data Encryption
Standard (DES) in 1977.
History of DES (2)

DES has been implemented in a majority of commercial
products and in the applications of almost all government
agencies

In January 1988, NSA stopped endorsing DES


DES had been so popular for so long, it would surely be targeted
for penetration and become useless as an official standard.
NSA wanted to move on to a newer, more secure, and less
popular algorithm as the new standard.
History of DES (3)

In 1998, the Electronic Frontier Foundation built a
computer system “DES cracker” for $250,000

DES cracker broke DES in three days

uses a brute force attack against the keyspace
Concerns on DES

Concerns on DES

Design decisions not public -- mysteries S-box



NSA's involvement in the design, S-boxes may have
backdoors
key is too short
Eventually, DES was replaced by the Advanced
Encryption Standard (AES) by NIST
Breaking Encryption Algorithm

Breaking an encryption algorithm can take place
through brute force attacks or by identifying
weaknesses in the algorithm


Brute force attacks have increased in potency because
of the increased processing capacity of computers.
An encryption algorithm is broken if someone is able
to uncover a key used in an encryption process.
Q: Is a broken algorithm worthless?
Breaking Encryption Algorithm
Ans:

If breaking an encryption algorithm by identifying
weakness of the algorithm, the answer is YES;

If breaking an encryption algorithm by brute force
attack, the answer depends …

In proper implementations, we should be encrypting
data with session keys


A session key is good only for that one session
So even if one session key was uncovered, it may be
useless to the attacker
DES steps

DES is a symmetric block encryption algorithm.



64-bit blocks of plaintext go in, 64-bit blocks of ciphertext come
out.
A 64-bit key: 56 bits are the true key, and 8 bits are for parity.
DES steps:
1.
2.
Divides the message into 64-bit blocks and operates on them
one at a time.
The blocks are put through 16 rounds of transposition and
substitution functions.

3.
The order and type of transposition and substitution functions
depend on the value of the key that is used with the algorithm.
The result is 64-bit blocks of ciphertext.
DES Modes of operation (section 2.5)

DES has several distinct modes of operation



Each mode specifies how a block cipher will operate
Each mode are used in different situations for different results
Modes





Electronic Code Book (ECB)
Cipher Block Chaining (CBC) – the most common
Cipher Feedback (CFB)
Output Feedback (OFB)
Counter Mode (CM)
Cipher Block Chaining Mode (CBC)
In CBC, each block of plaintext, the key, and the
ciphertext from the previous block are processed in the
Algorithm  Chaining
IV
Cipher Block Chaining Mode (CBC)

Dependence (Chaining) among the blocks

Ciphertext is extracted and used from the previous block of text;



For the first block, we use a 64-bit initialization vector (IV)
to add randomness
This chaining effect means that a particular ciphertext block is
dependent upon all blocks before it, not just the previous block.
CBC produces different ciphertext when encrypting the
same plaintext in different block

More random ciphertext  less pattern can be revealed from
ciphertext
Initialization vectors (IVs)

Initialization vectors (IVs) are random values that are used
with algorithms to ensure that patterns are not created during
the encryption process.




IVs are used with keys
IVs do not need to be encrypted when being sent to the
destination.
If IVs are not used, then two identical plaintext values that are
encrypted with the same key will create the same ciphertext.
In CBC, if we choose a different IV each time we encrypt a
message, even if it is the same message, the ciphertext will
always be unique.
2DES and 3DES

Double-DES has a key length of 112 bits
A specific attack against Double-DES that reduces its
work factor to about the same as DES

Triple-DES is a quick fix to provide more protection
for sensitive data.


uses 48 rounds in its computation, which makes it
highly resistant to differential cryptanalysis
take up to three times longer than DES to perform
encryption and decryption
2DES

There has been interest to provide another algorithm
during the transition to AES -- preserve the existing
investment in software and hardware, increasing the
security

Double DES


C=E_K2(E_K1(M))
M=D_K1(D_K2(C))
Q: Is double DES more secure than DES?
Meet-in-the-Middle attack on 2DES



1.
2.
3.
4.
5.
Proposed by Diffie, Hellman (1977)
Main observation:
if C=E_K2(E_K1(M)), then X=E_K1(M)=D_K2(C)
Assume we have two pairs of plaintext-ciphertext,
Encrypt P for all 2^56 possible keys K1
Store the results in a table and sort the table by the values of
X
Decrypt C using all possible 2^56 possible keys K2
For each decryption check the result in the table
In case of match, test the two keys with the second pair of
plaintext-ciphertext. If they match, the correct keys were found
2DES
Q : Is double DES more secure than DES?
Ans: through analysis, 2DES is broken in 2^56 steps with
probability larger than 1-2^-16.
The effort is not much bigger than the 2^55 required to
break DES
3DES

3DES is incorporated in 1999 with FIPS 46-3



Formula
FIPS 46-3 guidelines
AES is intended to replace 3DES
3DES

Counter to the meet-in-the-middle attack: use three
stages of encryption

3DES can work in different modes:
 DES-EEE3
E_K3( E_K2 ( E_k1(M) ) )
 DES-EDE3
E_K3( D_K2( E_K1(M) ) )
 DES-EEE2
E_K1( E_K2 ( E_k1(M) ) )
 DES-EDE2
E_K1( D_K2( E_K1(M) ) )
Advanced Encryption Standard (AES)


NIST sponsored a competition in 1997 to create a
replacement for DES.
The following five algorithms were the finalists:








MARS
RC6
Serpent
Twofish
Rijndael
The winner is the Rijndael algorithm by two Belgians
Use three different key lengths: 128 bits, 192 bits,
256 bits
was approved for use by U.S. government agencies
in May 2002
AES Features

Not a Feistel structure
Process the entire data block in parallel using
substitutions and permutation


The key is expanded into an array of 44 32-bit
words w[i]. Four distinct words (128 bits) serve as a
round key.
Four different stages

One permutation and three of substitution




Substitute bytes
Shift rows
Mix columns
Add round key
History of cryptography

The first encryption methods date back to
4000 years ago.


Some Egyptian hieroglyphics were encrypted
Atbash Cipher a Hebrew cryptographic method
the alphabet to be flipped so that each letter in the original
alphabet was mapped to a different letter in the flipped, alphabet.
ABCDEFGHIJKLMNOPQRSTUVWXYZ
ZYXWVUTSRQPONMLKJIHGFEDCBA

e.g.:
Encypt “atbash”  ?
Decrpt “hvxfirgb”  ?
Scytale Cipher (review)

Scytale cipher 400 B.C. the Spartans



Write a message on a sheet of papyrus that was
wrapped around a staff;
The papyrus was delivered and wrapped around a
different staff by the recipient;
The message was only readable if it was wrapped
around the correct size staff, which would make the
letters properly match up
32
Caesar Cipher (review)
Julius Caesar (100–44 B.C.) developed a simple
encryption method -- shifted the alphabet by three
positions
Standard Alphabet:
ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cryptographic Alphabet:
DEFGHIJKLMNOPQRSTUVWXYZABC
Example:
Encypt “caesar”  ?
Decrpt “vhfxulwb”  ?
Substitution Cipher (review)

Both Atbash cipher and Caesar Cipher are substitution
cipher, because each character is replaced with another
character.


Monoalphabetic substitution cipher: uses only one alphabet,
Polyalphabetic substitution cipher: uses multiple alphabets
Q1. Can you formulate them use mathematically?
Hint:
integers 0 – 25 represent 26 characters;
m: message / plaintext, c: cipher text;
encryption: c = E(m) = ?
decryption: m = D(c) = ?
Q2. Is Scytale cipher a substitution cipher?
Transposition Cipher (review)
Transposition Cipher: rearrange letters in plaintext
to produce cipher text


Scytale cipher is a transposition cipher
Rail-Fence cipher is another transposition cipher
 Plaintext is HELLO WORLD
 Encryption: c = E(m)
HLOOL
ELWRD
 HLOOLELWRD
 Describe decryption process: m = D(c) = ?
Vigenère Cipher

The Vigenère cipher is a method of
encryption that uses a series of different
Caesar ciphers based on the letters of a
keyword.
Appears to be unbreakable.
The Vigenère cipher has been reinvented many
times.
 The method was originally described by Giovan
Batista Belaso in his 1553 book La cifra del. Sig.
Giovan Batista Belaso
 However, the scheme was later misattributed to
Blaise de Vigenère in the 19th century, and is
now widely known as the "Vigenère cipher".

36
Terms in Vigènere Cipher

Vigènere table: a table used to encipher and decipher
Vigènere cipher has key letters on top, plaintext
letters on the left.



There are 27 shift alphabets
Vigènere cipher is a polyalphabetic substitution cipher. In
contrary, Caesar cipher is a monoalphabetic substitution
cipher
Key is used with Vigènere table in encryption /
decryption
The Vigènere Table
A
B
E
H
L
O
S
T
Y
G
G
H
L
N
R
U
Y
Z
E
I
I
J
M
P
T
W
A
B
H
V
V
W
Z
C
G
J
N
O
T
A mini example
Encryption:
A key letter V, and a
plaintext letter T  follow
V column down to T row
 “O”
Decryptioin:
A key letter V, and a
ciphertext letter O  “T”
Vigènere Cipher Example

If the message is longer than the key, the key repeats itself

E.g. 1:
Key: LEMON
Encrypt plaintext: ATTACKATDAWN
Key
L
E
M O
N
L
E
M
O
N
L
E
m
A
T
T
C
K
A
T
D
A
W
N
A
c

E.g.2, Decrypt ciphertext: P R U U Z L
Q: How to represent Vigènere Cipher in formula?
(Hint: encryption / decryption is done character by character)
Exercise
1) Encrypt a plaintext with the key “lucky”
computinggivesinsight
2) Decrypt a ciphertext with the key “vector”
olklwjvrgqodkpghtkcixbuviitxqzklgk
Cryptanalysis

Cryptanalysis is the science of studying and breaking
the secrecy of encryption processes, compromising
authentication schemes, and reverse-engineering
protocols.


All previously introduced ciphers have been broken.
Basic methods:


Statistical analysis
Exhaustive search key space
Statistical analysis
Each character has a certain frequency. A.k.a. 1-gram
model of English

a
0.080
h
0.060
n
0.070
t
0.090
b
0.015
i
0.065
o
0.080
u
0.030
c
0.030
j
0.005
p
0.020
v
0.010
d
0.040
k
0.005
q
0.002
w
0.015
e
0.130
l
0.035
r
0.065
x
0.005
f
0.020
m
0.030
s
0.060
y
0.020
g
0.015
z
0.002
Statistical Analysis (1)

f(c) frequency of character c in ciphertext

p(x) is frequency of character x in English

(i) correlation of frequency of letters in ciphertext with
corresponding letters in English, assuming key is i
(i) = 0 ≤ c ≤ 25 f(c)p(c – i)
Statistical Attack (2)

E.g., a Caesar cipher : KHOOR ZRUOG
step 1: Compute frequency of each letter in ciphertext:
G 0.1
H 0.1
K 0.1
O 0.3
R 0.2
U 0.1
Z 0.1
Step 2: Compute correlation  for key i
(i) = 0.1p(6 – i) + 0.1p(7 – i) + 0.1p(10 – i) +
0.3p(14 – i) + 0.2p(17 – i) + 0.1p(20 – i) +
0.1p(25 – i)
Correlation: (i) for 0 ≤ i ≤ 25
i
(i)
i
(i)
i
(i)
i
(i)
0 0.0482
7 0.0442
13 0.0520
19 0.0315
1 0.0364
8 0.0202
14 0.0535
20 0.0302
2 0.0410
9 0.0267
15 0.0226
21 0.0517
3 0.0575
10 0.0635
16 0.0322
22 0.0380
4 0.0252
11 0.0262
17 0.0392
23 0.0370
5 0.0190
12 0.0325
18 0.0299
24 0.0316
6 0.0660
25 0.0430
The Result
Step 3: find the most probable keys, based on :

i = 6, (i) = 0.0660


i = 10, (i) = 0.0635


plaintext HELLO WORLD
i = 14, (i) = 0.0535


plaintext AXEEH PHKEW
i = 3, (i) = 0.0575


plaintext EBIIL TLOLA
plaintext WTAAD LDGAS
The only valid English phrase is for i = 3. That’s the key
(3 or ‘D’)
Exhaustive search

Exhaustive search

If the key space is small enough, try all possible keys
until you find the right one
Q 1: How large is the key space in Caesar cipher ?
Q2: If we use exhaustive search, what is the expected
number of trials when breaking Caesar cipher?
Q3: How about the key space of Vigènere Cipher?
Q4: How to break Vigènere Cipher?
Attacking Vigènere Cipher
–
Vigenere ciphers were regarded by many as
practically unbreakable for 300 years.
–
In 1863, a Prussian major named Kasiski proposed a
method for breaking it.
–
This method was not in fact invented by Kasiski but instead
by Charles Babbage;
–
Babbage's discovery was used to aid English military
campaigns, and was not published until several years later;
as a result credit for the development was instead given to
Friedrich Kasiski
Statistical analysis of Vigènere Cipher
1.
Establish period n (the length of key)
2.
Break cipher into n parts, each part being enciphered
using the same key letter
3.
Solve each part  leverage one part from another
We want to break this cipher:
ADQYS
EQOOG
MOCIO
HSNEW
HCEUT
HIUIX
MIUSB
IFBAG
EQOOG
VECNE
QOIOF
OXKKT
KAUMF
BMBFV
DLAAV
MEGJS
MIBHK
VVTAA
ZGGWP
RWKXS
WTPCH
IZOOO
CIDTW
CIEKQ
VNSVP
AJMOC
Step 1. Establish Period n

Important observation: Repetitions in the ciphertext
occur when characters of the key appear over the same characters in the
plaintext

e.g.
Key VIGVIGVIGVIGVIGV
plain THEBOYHASTHEBALL
cipher OPKWWECIYOPKWIRG
Repetitions in this example cipher
Letters
Start
End
Distance
Factors
MI
5
15
10
2, 5
OO
22
27
5
5
OEQOOG
24
54
30
2, 3, 5
FV
39
63
24
2, 2, 2, 3
AA
43
87
44
2, 2, 11
MOC
50
122
72
2, 2, 2, 3, 3
QO
56
105
49
7, 7
PC
69
117
48
2, 2, 2, 2, 3
NE
77
83
6
2, 3
SV
94
97
3
3
CH
118
124
6
2, 3
Estimate of Period n

A long repetition “OEQOOG” and “MOC” are probably
not coincidence

Their distances are 30 and 72. The greatest common
divisor of 30 and 72 is 6.

many other shorter repetitions have 2 and 3 in their
factors

Thus the estimate period n = 6

Verify Period n by Friedman test (we skip this part)
Step 2: Break cipher into n parts
Key-1: AIKHOIATTOBGEEERNEOSAI
Key-2: DUKKEFUAWEMGKWDWSUFWJU
Key-3: QSTIQBMAMQBWQVLKVTMTMI
Key-4: YBMZOAFCOOFPHEAXPQEPOX
Key-5: SOIOOGVICOVCSVASHOGCC
Key-6: MXBOGKVDIGZINNVVCIJHH
Statistical Analysis each part
Counting characters in each part
ABCDEFGHIJKLMNOPQRSTUVWXYZ
1.
2.
3.
4.
5.
6.
31004011301001300112000000
10022210013010000010404000
12000000201140004013021000
21102201000010431000000211
10500021200000500030020000
01110022311012100000030101
Compare with unshifted alphabet frequencies in English:
HMMMHMMHHMMMMHHMLHHHMLLLLL
Solve each part (2)




First part: matches characteristics of unshifted
alphabet A  A
Third part : I  A
Sixth part : V  A
Substitute into ciphertext:
ADIYS RIUKB OCKKL MIGHKAZOTO EIOOL
IFTAG PAUEF VATAS CIITW EOCNO EIOOL
BMTFV EGGOP CNEKIHSSEW NECSE DDAAA
RWCXS ANSNP HHEUL QONOF EEGOS WLPCM
AJEOC MIUAX
Solve each part (3) further analysis

AJE in last line suggests “ARE”, meaning second
alphabet maps A into S:
ALIYS
MIOOL
EOCNO
HSSEE
HHECL
MICAX
RICKB
INTAG
MIOOL
NECSE
QONON
OCKSL
PACEF
BUTFV
LDAAA
EEGOS
MIGHS
VATIS
EGOOP
RECXS
ELPCM
AZOTO
CIITE
CNESI
ANANP
AREOC
Solve each part (4) further analysis

MICAX in last line suggests “mical” (a common ending
for an adjective), meaning fourth alphabet maps O into
A:

QI means that U maps into I, as Q is always
followed by U:
ALIMS
PACET
CNESI
EONON
RICKP
VATIS
VSSEE
ESGOS
OCKSL
QIITE
NSCSE
ELDCM
AIGHS
ECCNO
LDOAA
ARECC
ANOTO MICOL INTOG
MICOL BUTTV EGOOD
RECLS ANAND HHECL
MICAL
Got It!
ALIME
PACET
ONESI
EANON
RICKP
HATIS
VESEE
ESSOS
ACKSL
QUITE
NSOSE
ELDOM
AUGHS
ECONO
LDOMA
ARECO
ANATO MICAL INTOS
MICAL BUTTH EGOOD
RECLE ANAND THECL
MICAL
Note that: Vigenere cipher is easy to break by hand. However,
the principle of cryptanalysis hold for more complex ciphers
that can be implemented only by computer.
The War Machines: The Purple Machine

The Purple Machine is developed and used by the
Japanese during World War II


Employed techniques discovered by Herbert O. Yardley
The code was broken by William Frederick Friedman

Known as the “Father of U.S. Cryptanalysis”
59
The War Machines: Enigma

Enigma is developed by Arthur
Scherbius




Used by the Germans during World War II
Enigma substituted each letter typed by an
operator
Substitutions were computed using a key
and a set of switches or rotors
The code was broken first by a group of
Polish cryptographers

The machine for breaking the code was
called the “Bombe”
60
Design of Enigma Machine
An electrical voltage applied to the Q terminal on the top
row will appear at the L terminal on the bottom row.
61
How to use the Enigma machine?
1.
The originator configures the Enigma machine to its
initial settings;
1.
Type in the first letter of the message, and the machine
would substitute the letter with a different letter;

2.
The encryption was done by moving the rotors a predefined
number of times
Advance the rotors and enter the next letter.
Each time a new letter was to be encrypted, the operator
would advance the rotors to a new setting.
62
Mechanism of the Enigma Machine


The chosen substitution for each letter was
dependent upon the rotor setting
Assumption: the operators at each end needed to
know


the key - the initial setting, which is the crucial and
secret part of this process
And how to advanced the rotors when encrypting and
decrypting a message
Random and Pseudorandom Numbers

A number of network security algorithms based on
cryptography


Examples: generation of keys for RSA, generation of
stream key for symmetric stream cipher, generation of
session key, used in Kerberos for handshaking to
prevent replay attacks
Two requirements


Randomness
unpredictability
Randomness and Unpredictability

Randomness

Criterion to validate randomness


Uniform distribution
Independence



Tests to demonstrate if a sequence is NOT independent
Apply a number of such tests until the confidence that
independence exists is sufficiently strong
Unpredictability


“true” random sequence, numbers are unpredictable
However, in pseudorandom sequence, care must be
taken for unpredictability
Pseudorandom Numbers

Algorithms are deterministic



Numbers generated by algorithm are NOT statistically
random!
A good algorithm generates Pseudorandom Numbers
pass many reasonable tests of randomness
TRNG, PRNG, and PRF (page 39 – 40)


Entropy source
Seed
PRNG algorithms

Purpose-built algorithms:


E.g. RC4
Algorithms based on existing cryptographic
algorithms



Symmetric block cipher
Asymmetric cipher
Hash functions, and message authentication codes
Stream Cipher

What is stream cipher?


Keystream
Stream cipher is faster and use less code than block
cipher




However this advantage has diminished with the
introduction of AES
E.g. IBM AES instruction set
Stream cipher is better encrypt/decrypt of a stream of
data over a communication channel
Block cipher can reuse keys, stream cipher cannot.
Stream Cipher

Design considerations for a stream cipher



Encryption sequence should have a large period
Keystream should approximate the properties of a true
random number stream.
The key needs to be sufficiently long >= 128 bits
RC4




Designed in 1987 by Ron Rivest For RSA Security
RC4 was kept as trade secret by RSA Security, until
algorithm was anonymously posted on the Interne in
1994
RC4 algorithm is very simple
Used in SSL/TLS standards, WEP and WPA
RC4

A variable length key of from 1 to 256 byes is used
to initialize a 256-byte state vector S





S[0], S[1] .. S[255] contains a permutation of all 8-bit
numbers from 0 to 255.
A byte k is generated from S by selecting one of the
255 entries in a systematic fashion. As each value of
k is generated, the entries in S are once again
permuted.
Initialization of S
Stream generation
Encrypt and decrypt
RC4 Strength


Not any practical approach against RC4 with a
reasonable key length, such as 128 bits
WEP vulnerability is not with RC4 itself, but the way
in which keys are generated for use as input to RC4
One-Time Pad

A one-time pad is a perfect encryption scheme
because it is considered unbreakable if implemented
properly

Is made up of random bits.

Is as simple as letter substitution

This encryption process uses a binary mathematic
function XOR.
Message stream
1001010111
Keystream
0011101010
Ciphertext stream
1010111101
OTP in action

One-time pads have been used throughout history to
protect different types of sensitive data.

Today, they are still in place for many types of militaries as
a backup encryption option if current encryption processes
are unavailable for reasons of war or attacks.
A Russian One-time pad, captured by MI5
The history of cryptography
(reading assignment -- article 1)
Another way to hide data: Steganography

Steganography is a method of hiding data in another media
type so that the very existence of the data is concealed.



E.g.1 the least significant bit of each byte of the image can be
replaced with bits of the secret message.


does not use algorithms or keys to encrypt information.
A message can be hidden in a WAV file, in a graphic, or in unused
spaces on a hard drive or sectors that are marked as unusable.
This practice does not affect the graphic enough to be detected.
E.g. 2 can also be used to insert a digital watermark on digital
images so that illegal copies of the images can be detected.
Steganography
στεγανός
covered
γραφία
writing
the art and science of writing hidden messages in such a
way that no one, apart from the sender and intended
recipient, suspects the existence of the message
Steganography in Ancient Greece
-- Tattoo message on head
An ancient Greek historian Herodotus reports that messages
were tattooed onto the shaved heads of slaves. Once the hair
grew back, the slaves were sent to the recipient, with the
message hidden “in plain sight”.
Steganography in World War I
-- Null Cipher
The message below was sent by the German
embassy in World War I.
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.
Taking the first letter in each word of message reveals the
hidden text: PERSHING SAILS FROM NY JUNE 1.
Steganography in Espionage
-- Invisible ink
Spies use milk, fruit juice or urine as invisible inks,
which darken when heated.
An FBI agent is shown using
ultraviolet light to read secret
writing on a paper from a
suspected spy case
Steganography in Modern Days


Digital media lend themselves to steganography
because of the large amount of information in
certain file types
Steganography Carrier Files:






bmp
jpeg
gif
wav
mp3
Amongst others…
Steganography Terminology
Carrier File
Carrier File with
Hidden Message
Some Steganography Tools








Steganos
S-Tools (GIF, JPEG)
StegHide (WAV, BMP)
Invisible Secrets (JPEG)
JPHide
Camouflage
Hiderman
And many others…
(We will try it today …)
RGB Color Model in Image Files

red, green, and blue light are added together in
various ways to reproduce a broad array of colors.
(0, 0, 0) is black
(255, 255, 255) is white
(255, 0, 0) is red
(0, 255, 0) is green
(0, 0, 255) is blue
(255, 255, 0) is yellow
(0, 255, 255) is cyan
(255, 0, 255) is magenta
A Common Technique of Steganography
-- LSB

The simplest and most common type of steganography is
LSB (least significant bit). The one’s bit of a byte is
used to encode the hidden information.

Suppose we want to encode the letter A (ASCII 65 or
binary 01000001) in the following 8 bytes of a carrier file.
01011101 11010000 00011100 10101100
11100111 10000111 01101011 11100011
becomes
01011100 11010001 00011100 10101100
11100110 10000110 01101010 11100011
Left image is original JPEG file
Right image is with hidden message
Steganography Application
-- UV Watermarking
Steganography Tools
A list of over 100 steganography tools:
http://www.jjtc.com/Steganography/toolmatrix.htm
Some of them run in Linux platform







JPHS (JPHide JPSeek, JP hide and seek)
http://linux01.gwdg.de/~alatham/stego.html
Steghide
Outguess
Blindside
Gifshuffle
GzSteg
Etc.
Steganalysis

Steganalysis is the counter-measure against
steganography.


Attempts to analyze a data stream to determine
whether or not it contains hidden messages.
Steganography is



It’s fun to play with
Easy to implement but fairly effective.
Obviously has a lot of good and bad applications, as
with an technology.