Cryptography and Encryptions,Network Security,Caesar Cipher

Security Concept
Mr.Gopal Sakarkar
Mr. Gopal Sakarkar

Today’s Agenda
• Introduction of Security Concept.
• Principal of Security.
• Classification of Security Attacks
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Digital
Security
Computer
Security
Network
Security
Mr. Gopal Sakarkar

Need of Network Security
• According to FBI statistics result (2007) , up
to five billion dollars is lost each year due to
black holes .
• Loss of important data. e.g. Credit Card, ATM Card
• Confidential information of business have
been stolen by competitors. e.g. ICICI vs HDFC
• Last but not least : Important data stolen from
military .
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So, what do you mean by NS?
• It is vital component in information security
for securing all information passed through
computers network.
• It provide management policy for access
controls protection for H/W, S/W &
information in networking.
Mr. Gopal Sakarkar

Principal of Security
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• Confidentiality
• Authentication
• Integrity
• Non-repudiation

Confidentiality
• It specifies that only sender and intended
recipient(s) should be able to access the
contents of message.
e.g.: e-mail send by person A to person B.
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Authentication
• It help to establish proof of identities.
e.g. : Login using Userid and Password.
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Integrity
• Integrity means that changes need to be done
only by authorized entities and through
authorized mechanisms.
e.g. Updating bank account information
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Non-repudiation
• Non- repudiation does not allow the sender or
receiver of a message to refuse the claim of not
sending or receiving that message.
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Classification of Security Attacks
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Passive Attack
• A passive attack make use of information from
the system but does not affect system resource.
Passive
Attack
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Release of
Message Contents
Traffic Analysis

Release of Message Contents
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Hi, I am Bob
Hi, I am Bob
Hi, I am Bob

Passive
Attack
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Release of
Message Contents
Traffic Analysis

Traffic Analysis
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Meet me at
Cinemax
Phhw ph dw
flqhpda
Meet me
at
Cinemax

Active Attack
• It involve some modification of data stream or creation of a
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false stream.
Active
Attack
Replay Modification
Denial of
Service Masquerade

Replay
It involves passive capture of data unit and its
subsequent retransmission to produce an unauthorized
effect.
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Transfer Rs.1000
to Alice.
Transfer
Rs.1000 to
Darth.

Active
Attack
Replay Modification
Denial of
Service Masquerade
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Modification
In which some portion of message is altered or that message
are delayed or reordered to produce an unauthorized affect.
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Transfer Rs.1,000
to Darth.
Transfer
Rs.10,000
to Darth.
Transfer Rs.10,000
to Darth

Denial of service
It have a specific target (Server), in which prevents or
inhabits the normal use or management of communication
facilities.
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Masquerade
A masquerade is a type of attack where the attacker act as an authorized user system in order to gain access to it or to gain greater privileges than they
are authorized for.
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Summary
• Four goals have been defined for security
i.e. Confidentiality , Authentication, Integrity,
Non-repudiation.
• Security Attacks are classified in two parts
Active and Passive.
Mr. Gopal Sakarkar

For Further Reading
• http://www.smartchip.com/flash/presentationV2.swf
• http://buchananweb.co.uk/asmn/unit03.swf
• http://www.computing.co.uk/computing/video/2246841/network-security
• http://en.kioskea.net/contents/courrier-electronique/fonctionnement-mta-mua.php3
• http://www.thepcmanwebsite.com/cgi-bin/web_tools/ascii.pl (converter)
• http://bytes.com/topic/c/answers/769137-how-convert-alphabet-numbers
• http://www.kerryr.net/pioneers/binary.htm
• http://services.exeter.ac.uk/cmit/modules/the_internet/slides/ch01s01s04.html (packet working)
Mr. Gopal Sakarkar

32
Caesar Cipher
It is a substitution cipher invented by Julius Caesar.
It replace each letter of the alphabet with the letter standing thired
Place further down the alphabet.
Let numerical equivalency of letter
A B C D E F G H …… z
0 1 2 3 4 5 6 7 25

33
Caesar Cipher
Let , for each plaintext letter p, substitute the cipher letter :
C=E(3,p)=(p+3) mod 26
For generalize equation for encryption :
C=E(k,p)= (p+k) mod 26
For generalize equation for decryption :
P=D(k,C)=(C-K)mod 26

34
Caesar Cipher
plain: abcdefghijklmnopqrstuvwxyz
key: defghijklmnopqrstuvwxyzabc
cipher: PHHW PH DIWHU WKH WRJD SDUWB
plain: MEET ME AFTER THE toga PARTY
Video

35
“Rail-Fence” Cipher
It is use substitution method , in which plaintext is written down
As a sequence of diagonals and then read off as a sequence of
row.

36
“Rail-Fence” Cipher
DISGRUNTLED EMPLOYEE
D R L E O
I G U T E M L Y E
S N D P E
DRLEOIGUTE MLYESNDPE

What is Steganography?
Stegosaurus: a covered lizard
(but not a type of cryptography)
Greek Words:
STEGANOS – “Covered”
GRAPHIE – “Writing”
• Steganography is the art and science of writing
hidden messages in such a way that no one apart
from the intended recipient knows of the existence
of the message.
• This can be achieve by concealing the existence of
information within seemingly harmless carriers
or cover
• Carrier: text, image, video, audio, etc.

Modern Steganography Techniques
Masking and Filtering: Is where information is hidden inside of a image using
digital watermarks that include information such as copyright, ownership, or
licenses. The purpose is different from traditional steganography since it is
adding an attribute to the cover image thus extending the amount of
information presented.
Algorithms and Transformations: This technique hides data in mathematical
functions that are often used in compression algorithms. The idea of this
method is to hide the secret message in the data bits in the least significant
coefficients.
Least Significant Bit Insertion: The most common and popular method of
modern day steganography is to make use of the LSB of a picture’s pixel
information. Thus the overall image distortion is kept to a minimum while
the message is spaced out over the pixels in the images. This technique
works best when the image file is larger then the message file and if the
image is grayscale.

Basics of Modern Steganography
fE: steganographic function "embedding"
fE-1: steganographic function "extracting"
cover: cover data in which emb will be hidden
emb: message to be hidden
key: parameter of fE
stego: cover data with the hidden message

Important Requirement for
Steganographic System
• Security of the hidden communication
• size of the payload
• Robustness against malicious and
unintentional attacks

45
Basic Types of Ciphers
• Transposition ciphers – rearrange bits
or characters in the data
• Substitution ciphers – replace bits,
characters, or blocks of characters with
substitutes

46
Encryption Methods
• The essential technology underlying virtually
all automated network and computer security
applications is cryptography
• Two fundamental approaches are in use:
– Conventional Encryption, also known as
symmetric encryption
– Public-key Encryption, also known as
asymmetric encryption

47
Conventional Encryption
Model

48
Five components to the algorithm
– Plaintext: The original message or data
– Encryption algorithm: Performs various substitutions
and transformations on the plaintext
– Secret key: Input to the encryption algorithm.
Substitutions and transformations performed depend
on this key
– Ciphertext: Scrambled message produced as output.
depends on the plaintext and the secret key
– Decryption algorithm: Encryption algorithm run in
reverse. Uses ciphertext and the secret key to produce
the original plaintext

50
M EK C DK M
EK defined by an encrypting algorithm E
DK defined by an decrypting algorithm D
For given K, DK is the inverse of EK, i.e.,
DK(EK(M))=M
for every plain text message M

Today’s Agenda
• Cryptography and Encryption
• Encryption Principles
• Feistel Cipher Structure
• Data Encryption Standard (DES)
Mr. Gopal Sakarkar

Cryptography
• It is a Greek word , means that “Secret
Writing”.
• Cryptography is an art and science for
achieving security by encoding the readable
format data in to a non-readable form.
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Encryption
Encryption is a process of converting the plain text data in to ciphertext data.
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Encryption Principles
• An encryption scheme has five ingredients:
– Plaintext
– Encryption algorithm
– Secret Key
– Ciphertext
– Decryption algorithm
• Security depends on the secrecy of the key, not the
secrecy of the algorithm.
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Average time required for exhaustive key
search
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Key Size
(bits)
Number of
Alternative Keys
Time required at
106 Decryption/μs
32 232 = 4.3 x 109 2.15 milliseconds
56 256 = 7.2 x 1016 10 hours
128 2128 = 3.4 x 1038 5.4 x 1018 years
168 2168 = 3.7 x 1050 5.9 x 1030 years

Conventional Encryption Model
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Cryptography Process Depend on….
1. The type of operations used for transforming plaintext to
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ciphertext.
1.1 Substitution
1.2 Transpose
2. The number of keys used
2.1 Symmetric (single key)
2.2Asymmetric(two-keys,orpublic-key encryption)
3. The way in which the plaintext is processed
Block Cipher Stream Cipher

Substitution Process
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Transposition Techniques
• Consider plain text message as a number
A=0 , B=1, C=2……..Z=25.
• Take plain text CAT =
2
0
19
Take N x N matrix of randomly chosen keys.
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6 24 1
13 16 10
20 17 15
=
Multiply two matrix
6 24 1
13 16 10
20 17 15
2
0
X 19 =
31
216
325

• Now compute a mod 26 value of the above
matrix.
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31
216
325
mod 26
5
8
= 13
Now translate number to alphabet
5=F, 8=I and 13= N i.e. cipher text is FIN

Exercise - II
• Define a symmetric-key cryptography.
• Distinguish between a block cipher and a stream
cipher with an example.
• Decrypt a above example by taking a inverse of
8 5 10
21 8
21
21 12 8
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original matrix i.e.
• Draw an algorithm , flowchart and write a C++
program for implementing Transposition
Techniques.

Summary
• Definition of Cryptography .
• Working of encryption principal.
• Substitution and transportation techniques .
Mr. Gopal Sakarkar

For Further Reading
• http://buchananweb.co.uk/asmn/unit04.swf
• http://www.youtube.com/watch?v=IzVCrSrZIX8
• http://www.youtube.com/watch?v=ZdC7cnpYOwI&feature=related
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Confusion and Diffusion
• Introduced by Claude Shannon to capture the two basic building blocks for any
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cryptographic system.
• Confusion - Confusion seeks to make the relationship between the statistics of the
ciphertext and the value of the encryption key as complex as possible, again to
stop attempts to discover the key.
• Diffusion - The mechanism of diffusion seeks to make the statistical relationship
between the plaintext and ciphertext as complex as possible in order to prevent
attempts to assume the key.

Approximate Alphabet Frequency
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Feistel Cipher Structure
• It is block cipher symmetric encryption algorithms, first described by
Horst Feistel of IBM in 1973.
• It is depends on the choice of the following parameters
• Block size: larger block sizes mean greater security
• Key Size: larger key size means greater security
• Number of rounds: multiple rounds offer increasing security
• Subkey generation algorithm: greater complexcity will lead to greater
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difficulty of cryptanalysis.
• Fast software encryption/decryption: the speed of execution of the
algorithm becomes a concern.

Steps:
1. Input of plaintext with length 2w bits and key K.
2. Plaintext is divided into two halves L0 and R0.
3. These two halves pass through N round of processing to
produce CipherText block.
4. The key K is derived from subkey generation algo.
5. These two halves combine by applying a round function
‘F’ on right half of data and then taking
X-OR operation of the output of F with left half of data.
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Exercise
• List out the various Feistel ciphers Algorithm and explain each
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in brief.

For Further Reading
• http://www.quadibloc.com/crypto/co040906.htm
• http://www.encryptionanddecryption.com/encrypt_decrypt_encyclopedia.ht
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ml

Data Encryption Standard (DES)
I. It is a Block Cipher Symmetric algorithm.
II. It takes 64 bits plaintext and 56 (64) bits as a key.
III. It produce a 64 bits cipher text.
IV. It consist of 16 steps , called round.
Steps:
1. It take 64 bit plain text as given i/p to Initial Permutation Function (IPF).
2. IPF produce two halves, i.e. Left Plain Text (LPT) and Right Plain Text
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(RPT)
3.Now, each LPT and RPT goes through 16 rounds of encryption process
with key K(56 bits).
4.At the end , LPT and RPT are rejoined and a final permutation (FP) is
performed which is being the inverse of IP on the combined block.
5. Finally the result produced 64 bits cipher text.

Plain Text (64 bits)
Initial Permutation
LPT RPT
Key ( K) 16 Rounds 16 Rounds
56 bits
Final Permutation
Cipher Text(64 bits)
DES Algorithm
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DES Encryption Overview
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An Example
• Let M be the plain text message M = 0123456789ABCDEF,
where M is in hexadecimal (base 16) format.
Rewriting M in binary format, we get the 64-bit block of text:
• M = 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101
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1110 1111
• L = 0000 0001 0010 0011 0100 0101 0110 0111
• R= 1000 1001 1010 1011 1100 1101 1110 1111
The first bit of M is "0". The last bit is "1". We read from left to right.
Let K be the hexadecimal key K = 133457799BBCDFF1
K = 00010011 00110100 01010111 01111001 10011011 10111100 11011111
11110001
Cipher Text: 85E813540F0AB405.
Online Example

The EFF's US $ 250,000 DES cracking machine contained 1,856 custom chips
and could brute force a DES key in a matter of days — the photo shows a
DES Cracker circuit board fitted with several Deep Crack chips.
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Triple-DES with Two-Keys
• hence must use 3 encryptions
– would seem to need 3 distinct keys
• but can use 2 keys with E-D-E sequence
– C = EK1[DK2[EK1[P]]]
– no encrypt & decrypt equivalent in security
– if K1=K2 then can work with single DES
• standardized in ANSI X9.17 & ISO8732
• no current known practical attacks

Summary
• Security of data is depend on secrecy of key not on the
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encryption algorithm.
• Feistel Cipher Structure is basic structure for any symmentric
encryption algo.
• DES algorithm also called as DEA has been a cryptographic
alog. used from over four decades.
• It was adopted in 1977 by the National Bureau of Standards as
Federal Information Processing Standard 46 (FIPS PUB 46).

For Further Reading
• http://www.buchananweb.co.uk/asmn/unit03.swf
• http://williamstallings.com/Crypt-Tut/Crypto%20Tutorial%20-
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%20JERIC.swf
• http://orlingrabbe.com/des.htm (IMP)
• http://www.tero.co.uk/des/explain.php

Exercise - III
• Explain a triple DES in detail.
• Find out the various application in which DES is implemented.
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The Blowfish Encryption
Algorithm
• Developed by Bruce Schneier
• Keyed, symmetric block cipher
• Designed in 1993 .
• Can be used as a drop-in replacement for DES.

Algorithm (cont.)
• As a fast, free alternative to existing
encryption algorithms.
• Variable-length key.
• From 32 bits to 448 bits.

Algorithm (cont.)
• Fast: It used 32 bit microprocessors for 26
clock cycles per byte.
• Compact : It need less than 5 kb memory
for execution.
• Simple : It used primitive operations ,such
as addition , XOR ,etc.
• Secure : It has variable length key upto
448 bits long.
• Freely available source code
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Algorithm (cont.)
• Gained acceptance as a strong encryption
algorithm.
• Blowfish is unpatented and license-free, and is
available free for all uses.
• No effective cryptanalysis has been found to
date.
• More attention is now given to block ciphers with
a larger block size, such as AES or Twofish.

7.07. Blowfish Key Schedule
• uses a 32 to 448 bit key
• used to generate
– 18 32-bit subkeys stored in K-array Kj
– four 8x32 S-boxes stored in Si,j
• key schedule consists of:
– initialize P-array and then 4 S-boxes using pi
– XOR P-array with key bits (reuse as needed)
– loop repeatedly encrypting data using current P & S and
replace successive pairs of P then S values
– requires 521 encryptions, hence slow in re-keying

Blowfish Encryption
• uses two primitives: addition & XOR
• data is divided into two 32-bit halves L0 & R0
for i = 1 to 16 do
Ri = Li-1 XOR Pi;
Li = F[Ri] XOR Ri-1;
L17 = R16 XOR P18;
R17 = L16 XOR i17;
• where
F[a,b,c,d] = ((S1,a + S2,b) XOR S3,c) + S4,a

The Blowfish Algorithm: Encryption
(cont)
Diagram of Blowfish's F function

The Blowfish Algorithm: Encryption
(cont)
• Blowfish's F-function.
• Splits the 32-bit input into four eight-bit quarters, and
uses the quarters as input to the S-boxes.
• Outputs are added modulo 232 and XORed to produce
the final 32-bit output.
• Blowfish is a Feistel network, it can be inverted simply by
XORing P17 and P18 to the ciphertext block, then using
the P-entries in reverse order.

RC5
• It is symmetric key block encryption algorithm
developed by Ron Rivest.
• It is quite fast as it use only the primitive computer
operation i.e. XOR , addition, shift etc.
• It used variable number of round and variable bit-size
key.
• It required less memory for execution so that it not only
used for desktop computer but also for smart card and
other devices.
» 125
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RC5 Working
• It used the plain text block size of 32,64, or 128 bits.
• The key length can be 0 to 2040 bits.
• Number of rounds can be from 0 to 255.
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Divide plain text into two block
i.e. A ,B
Add A & S[0] to produce C
Add B & S[1] to produce D
Start with i=1
Check:
Is i>r ?
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1. XOR C & D to
produce E
4.XOR D & F to
produce G
2. Circular left shift E
by D bits
3. Add E & S[2] to
produce F
5. Circular left shift
G by F bits
6. Add G & S[2i+1]
to produce H
Increment i by 1
Call F as C (i.e. C=F)
Call H as D (i.e. D=H)
Stop
Yes
No

Lecture 3 Today’s Agenda
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• IDEA Algorithm.
• Cipher Block Chaining.
• Location of encryption devices.
• Key Distribution

International Data Encryption Algorithm
• It is one of the strongest cryptographic algorithm
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invented in 1992.
• It is Block Cipher Symmetric cryptographic alog.
with 64 bits plain text and 128 bits length key.
• It is used both substitution and transposition
techniques for encryption

Working of IDEA
1.It take a 64 bits plaintext block as input and then
partition it into four part, say P1 to P4.
2. P1 to P4 are the inputs to the first round of the
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algorithm.
3. It has eight round of encryption processing.
4. Each round use six-sub keys generated from original
key having 16 bits length.
5. Final step consist of an Output Transformation
Which use just four sub-keys , K49 to K52.

Working
Plain Text (64bits)
Round 1
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K 1
K 2
K 6
Round 2 ….
K 7
K 12
……………….
Round 6 K 43
K 48
Output Transformation
K 49
K 52
P1(16 bits) P2(16 bits) P3(16 bits) P4(16 bits)
….
….
….
….
C1(16 bits) C2(16 bits) C3(16 bits) C4(16 bits)
Cipher Text (64bits)

Working of Rounds
• Each round has a series of operation on the data block
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using six keys.
• Each round perform a lot of mathematical action such
as Multiplication, Addition and X-OR.
• Each round is divided into 14 steps.

Sub-key Generation Round
Unused
(97-128 bits) …
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• First round
Original
Key (128 bits)
K1(1-16 bits) K2(17-32 bits) K6(81-96 bits)

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• Second round
Unused
Key (97-128 bits)
K7 (97-112 bits) K8(113-128 bits)
What about key k9, k10…k12 for second round ?
Conti….

• The original key is exhausted . It is circular-left shifted by 25
Position 1 Position
… (65-128 bits)
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bits.
Original Key(128 bits)
128
circular-left shifted by 25 bits
Now start allocating fresh sub-key from K7 to K12
New Key(128 bits)
K9(1-16 bits) K10(17-32 bits) K12(49-64 bits)
Unused

Exercise - IV
• Explain in detail all eight round of sub key generation process.
• Find out the strength of IDEA algorithm.
Mr. Gopal Sakarkar

• Note:
• A permutation is "a re-arrangement of
elements of a set".
Exp. We do 4 x 3 x 2 x 1 = 24.
• There are 24 different ways that the letters
can be arranged.
• We can write 4!, which is read as "four
factorial."
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• Taking the 4 letters, ABCD, write down all
the permutations of 3 of these letters:
ABC BAC CAB DAB
ACB BCA CBA DBA
ABD BAD CAD DAC
ADB BDA CDA DCA
ACD BCD CBD DBC
ADC BDC CDB DCB
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Working of Substitution method
• S-Box= Substitution Box
• Example #1: Solve the following system using the substitution method
x + y = 20
x − y = 10
Step 1
You have two equations. Pick either the first or the second equation and solve for
either x or y.
Since I am the one solving it, I have decided to choose the equation at the bottom
(x − y = 10) and I will solve for x
x − y = 10
Add y to both sides
x − y + y = 10 + y
x = 10 + y
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• Step 2
Using x + y = 20, erase x and write 10 + y since x = 10 + y
We get 10 + y + y = 20
10 + 2y = 20
Minus 10 from both sides
10 − 10 + 2y = 20 − 10
2y = 10
Divide both sides by 2
y = 5
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• Step 2
• Now you have y, you can replace its value into either equation to get
x.
Replacing y into x + y = 20 gives
x + 5 = 20
Minus 5 from both sides
x + 5 − 5 = 20 − 5
x = 15
The solution to the system is x = 15 and y = 5
Indeed 15 + 5 = 20 and 15 − 5 = 10
• H/W: Solve the following system using the substitution method
3x + y = 10
-4x − 2y = 2
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Algorithm Modes
Algorithm
Modes
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Electronic Code
Book (ECB)
Cipher Block
Chaining (CBC)
Cipher FeedBack
(CFB)
Out FeedBack
(OFB)
Work on block
cipher
Work on stream
cipher

Electronic Code
Book (ECB)
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Algorithm
Modes
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Electronic Code
Book (ECB)
Cipher Block
Chaining (CBC)
Cipher FeedBack
(CFB)
Out FeedBack
(OFB)

Cipher Block
Chaining (CBC)
• Message is broken into blocks
• Linked together in encryption operation
• Each previous cipher blocks is chained with current plaintext
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block, hence name
• Use Initial Vector (IV) to start process
-IV has no special meaning , used to make each message
unique only.
• Uses: bulk data encryption, authentication

Cipher Block Chaining (CBC)
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Advantages and Limitations of CBC
• A ciphertext block depends on all blocks before it.
• Any change to a block affects all following ciphertext blocks
• Need Initialization Vector (IV)
– which must be known to sender & receiver
– if sent in clear, attacker can change bits of first block, and
change IV to compensate
– hence IV must either be a fixed value
– or must be sent encrypted in ECB mode before rest of
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message

Cipher FeedBack
(CFB)
• Message is treated as a stream of bits
• Added to the output of the block cipher
• Result is feed back for next stage (hence name)
• Standard allows any number of bit (1,8, 64 or 128 etc) to be
feed back
– denoted CFB-1, CFB-8, CFB-64, CFB-128 etc
Uses: stream data encryption, authentication
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Cipher FeedBack (CFB)
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Advantages and Limitations of CFB
• Appropriate when data arrives in bits/bytes
• Most common stream mode
• limitation is need to install while do block encryption after
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every n-bits
• Note that the block cipher is used in encryption mode at both
ends
• Errors propagate for several blocks after the error.

Output FeedBack (OFB)
• Message is treated as a stream of bits
• In CFB, the cipher text is fed into the next stage of
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encryption process.
• But in the OFB, the output of the IV encryption
process is fed into the next stage of encryption
process
• Output of cipher is added to message
• Output is then feed back (hence name)
• Feedback is independent of message
• uses: stream encryption on noisy channels.

OutpuMrt. GFoepael SdaBkarakacrk (OFB)

Key Distribution
Symmetric schemes require both parties to share a
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common secret key
Issue is how to securely distribute this key
Often secure system failure due to a break in the key
distribution scheme.

Key Distribution
• Given parties A and B have various key distribution
alternatives:
1. A can select key and physically deliver to B
2. third party can select & deliver key to A & B
3. if A & B have communicated previously can use previous
key to encrypt a new key
4. if A & B have secure communications with a third party C,
C can relay key between A & B
Mr. Gopal Sakarkar

Summary
• IDEA is a strongest encryption algorithm only because of its
Mr. Gopal Sakarkar
key length.
• Algorithm Modes of Operation
– ECB, CBC, CFB, OFB
Key distribution is centralize storage of keys .

Cryptography and Encryptions,Network Security,Caesar Cipher

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