# SOLUTION: Kent State University Encryption Rivest Cipher 4 Symmetric Key Algorithm Essay

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Computer Security
Fundamentals
by Chuck Easttom
Chapter 8 Encryption
Chapter 8 Objectives

Explain the basics of encryption
Discuss modern cryptography methods
Select appropriate cryptography for your
organization
Understand the function and protocols of
VPNs
Chapter 8 Encryption
2
Introduction

Encryption

Obfuscating the data so a key is required.
One critical part to the security puzzle.
Cryptography

Requires mathematics
Chapter 8 Encryption
3
Cryptography Basics

Decryption

Reversal of the scrambling protocol
Encryption

Algorithm scrambles plain text
Sender and receiver agree on algorithm

Message difficult to re-create without key

Chapter 8 Encryption
4
Cryptography Basics (cont.)

Two basic types

Single/symmetric key encryption

Stream
Block
▪ Substitution and transposition
Public/asymmetric key encryption
Chapter 8 Encryption
5
History of Encryption

Old as written communication and war
Caesar Cipher

Shift cipher

A DOG

Shift 1 – B EPH
Shift 2 – C FQI
Shift negative 1 – Z CNF
Chapter 8 Encryption
6
History of Encryption (cont.)

Caesar Cipher

Frequency distribution cracks this simple
cipher.
Substitution alphabet.

Substitutes one letter in the alphabet for
another.
Caesar is a mono-alphabetic cipher.
Chapter 8 Encryption
7
History of Encryption (cont.)

ATBASH
Rail Fence
Vigenere

Enigma

Chapter 8 Encryption
8
History of Encryption (cont.)

Multi-alphabetic

Select multiple shifts

Shift 1, 2, –1
Rotate through the shifts
A DOG becomes B FNH
Old cipher considered weak today
Chapter 8 Encryption
9
Binary Operations

Binary Operations

AND, OR, XOR
Example of AND operation
1 1 0 1
1 0 0 1
1 0 0 1
Chapter 8 Encryption
10
Binary Operations

Example of OR operation
1 1 0 1
1 0 0 1
1 1 0 1
Chapter 8 Encryption
11
Binary Operations

Example of XOR operation
1 1 0 1
1 0 0 1
0 1 0 0
Chapter 8 Encryption
12
Binary Operations

XOR only reversible binary operation

Convert plain text to ASCII
A DOG = 065 032 068 079 071

Then, convert ASCII to binary
0100 0001, 0100 0100, 0100 1111, 0100 0111
Chapter 8 Encryption
13
Binary Operations

XOR the ASCII
0100 0001, 0100 0100, 0100 1111, 0100 0111
1111 0111, 1111 0111, 1111 0111, 1111 0111
1011 0110, 1011 0011, 1011 1000, 1011 0000

Result is cipher text.
Chapter 8 Encryption
14
Cryptography Terms

Key: The bits that are combined with the
plain text to encrypt it. In some cases this
is random numbers; in other cases it is the
result of some mathematical operation.
Plain text: The unencrypted text.
Cipher text: The encrypted text.
Algorithm: A mathematical process for
doing something.
Chapter 8 Encryption
15
Modern Methods

Single key (symmetric) encryption

Same key to encrypt and decrypt

Blowfish

Symmetric block cipher
Works on “blocks” of letters
Uses variable length key (32–448 bits)
Freeware
Chapter 8 Encryption
16
Modern Methods (cont.)

Data Encryption Standard (DES)
1.
Divided into 64-bit blocks; then transposed
2. Manipulated by 16 steps of encryption, using
56-bit key
3. Scrambled by a swapping algorithm
4. Transposed one final time
Chapter 8 Encryption
17
Modern Methods (cont.)

algorithm eventually chosen to replace
DES. It is a block cipher that works on 128bit blocks. It can have one of three key
sizes of 128, 192, or 256 bits. This was
selected by the United States government
to be the replacement for DES and is now
the most widely used symmetric key
algorithm.
Chapter 8 Encryption
18
Modern Methods (cont.)

One major problem with symmetric key
encryption
How do you transmit the symmetric key?

Chapter 8 Encryption
19
Modern Methods (cont.)

Public key (asymmetric) encryption

One key (public key) used to encrypt .
One key (private key) used to decrypt.
Only holder of a private key can decrypt
messages.
Chapter 8 Encryption
20
Modern Methods (cont.)

Public key (asymmetric) encryption

Depends on large prime numbers, factoring,
and number theory.
Public key encryption is most widely used.
Pretty Good Privacy (PGP):

Freeware
Quite secure
Chapter 8 Encryption
21
Modern Methods (cont.)

Public key (asymmetric) encryption

Pretty Good Privacy (PGP)

Freeware
Phil Zimmerman – 2004
Quite secure
Chapter 8 Encryption
22
Modern Methods (cont.)
(http://web.mit.edu/network/pgp.html)
Chapter 8 Encryption
23
Modern Methods (cont.)

Public key (asymmetric) encryption

RSA

You start by generating two large random primes, p
and q, of approximately equal size. Now you need
to pick two numbers so that when multiplied
together the product will be the size you want (that
is, 1024 bits, 2048 bits, and so on).
Now multiply p and q to get n.
Let n = pq
Let m = (p – 1)(q – 1)
Chapter 8 Encryption
24
Modern Methods (cont.)

Chapter 8 Encryption
25
Modern Methods (cont.)
(http://www.rsasecurity.com)
Chapter 8 Encryption
26
Modern Methods (cont.)

Legitimate versus fraudulent encryption

Warning signs of frauds

Unbreakable
Certified
Inexperienced people
Chapter 8 Encryption
27

Unbreakable
Unhackable
Secret algorithm
Kerhoff’s principle
Chapter 8 Encryption
28
Digital Signatures

A digital signature is not used to ensure the confidentiality of a
message, but rather to guarantee who sent the message. This is
referred to as nonrepudiation. Essentially, it proves who the sender
is. Digital signatures are actually rather simple, but clever. They
simply reverse the asymmetric encryption process. Recall that in
asymmetric encryption the public key (which anyone can have
access to) is used to encrypt a message to the recipient, and the
private key (which is kept secure and private) can decrypt it. With a
digital signature, the sender encrypts something with his private key.
If the recipient can decrypt that with the sender’s public key, then it
must have been sent by the person purported to have sent the
message.
Chapter 8 Encryption
29
Hash

Hashing is a type of cryptographic algorithm
that has some specific characteristics. First
and foremost it is one way. That means you
cannot “unhash” something. The second
characteristic is that you get a fixed-length
output no matter what input is given. Finally,
it should have few or no collisions. A collision
is when two different inputs provide the same
output.
Chapter 8 Encryption
30
Hash – cont.

MD5
SHA1
SHA2
SHA3
Chapter 8 Encryption
31
3
2
VERY Simple Illustration of
Rainbow Tables
MD5 Hash (in Hex)
MD5 Hash (in Hex)
aaaa
74b87337454200d4d33
f80c4663dc5e5
aaaaa
594f803b380a41396ed
63dca39503542
aaab
4c189b020ceb022e0ec
c42482802e2b8
aaabb
120858a7016efcfab669
67b834e9153c
aaac
3963a2ba65ac8eb1c6e
2140460031925
aaacc
ee43671d755ac457cfe
6e32d1894788e
aaa1
dd872247e451f
aaa1a
5bbac29650eb36b4de1
6885c190a9fa3
aaa2
aaa2a
597f0ce6d11567cc691b
3f5df35594cb
aaa4
ee93fca7c150d9c548af
f721c87d0986
aaa4a
4305dc076b3ba2bf8d5
5524cddf5a72d
Chapter 8 Encryption
3
3
Hash – Salt

Random bits added to further secure encryption or hashing. Most often encountered with hashing, to
prevent Rainbow Table attacks.

Essentially the salt is intermixed with the message that is to be
hashed. Consider this example. You have a password that is
pass001
in binary that is
01110000 01100001 01110011 01110011 00110000 00110000
00110001
A salt algorithm would insert bits periodically, lets assume for our
example that we insert bits every 4th bit giving us
0111100001 0110100011 0111100111 0111100111 0011100001
0011100001 0011100011
If you convert that to text you would get
xZ7�� #

Chapter 8 Encryption
Historical Steganography

The ancient Chinese wrapped notes in wax
and swallowed them for transport.
In ancient Greece a messenger’s head might
be shaved, a message written on his head,
then his hair was allowed to grow back.
In 1518 Johannes Trithmeus wrote a book on
cryptography and described a technique
where a message was hidden by having each
letter taken as a word from a specific column.
Chapter 8 Encryption
Historical Steganography Continued

During WW II the French Resistance sent
messages written on the backs of couriers
using invisible ink
Microdots are images/undeveloped film the
size of a typewriter period, embedded on an
innocuous documents. These were said to be
used by spy’s during the Cold War.
Chapter 8 Encryption
Steganography Terms

Payload is the data to be covertly
communicated.
The carrier is the signal, stream, or data file
into which the payload is hidden. This is also
sometimes called the cover object.
The channel is the type of medium used.
Chapter 8 Encryption
3
7
Cryptanalysis

Ciphertext Only Attack
Known plain text
Chosen plain text
Related Key
Chapter 8 Encryption
Summary

Encryption is a basic element of security.
Encrypting data when transmitting is an
integral part of any security plan.
Chapter 8 Encryption
38

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