Cryptography -- ps.ppt

8/13/2019 Cryptography -- ps.ppt

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Course Objectives

Cryptographic Basic.

Modern Cryptographic

Key. Symmetric and Asymmetric Key.

Hashing Algorithm.

Symmetric Cryptography. DES, Triple DES, Blowfish, etc.

Key Distribution.


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Goals of Cryptography

Security practitioners utilize cryptographic

systems to meet Four Fundamental

Goals:

Confidentiality.

Integrity.

Authentication.

Non-Repudiation.


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Cryptography Concept


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Cryptography Basic


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Term Details

Plaintext A message in its natural format readable byan attacker.

Chipertext Message altered to be unreadable by anyoneexcept the intended recipients.

Key Sequence that controls the operation andbehavior of the cryptographic algorithm.

Keyspace Total number of possible values of keys in acrypto algorithm.


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All cryptographic algorithms rely on keys

to maintain their security.

Every algorithm has a specific key space.

The key space is the range of values that are

valid for use as a key for a specific algorithm.

A key space is defined by its bit size.


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The key space is the range between the

key that has all 0sand the key that has all

1s.

Or to state it another way, the key space is

the range of numbers from 0 to 2n, wherenis the bit size of the key.

Thus, a 128-bit key can have a value from

0 to 2128.


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Different Types of Key

In private key cryptosystems, allparticipants use a single shared key.

In public key cryptosystems, eachparticipant has their own pair of keys.


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Cryptography Mathematics:

Logical Operation The AND operation (represented by the

symbol) checks to see whether two values

are both true.


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Logical Operation The OR operation (represented by the

symbol) checks to see whether at least

one of the input values is true


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Logical Operation The NOT operation (represented by the ~

or ! symbol) simply reverses the value of

an input variable. This function operates

on only one variable at a time.


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Logical Operation The XOR function returns a true value

when only one of the input values is true.

If both values are false or both values are

true, the output of the XOR function is

false


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Modulo Function The modulo function is represented in

equations by the abbreviation mod,

although its sometimes represented by

the % operator.


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One Way Function

A one-way function is a mathematical

operation that easily produces output

values for each possible combination of

inputs but makes it impossible to retrievethe input values.

Cryptographers rely on functions that they

suspect may be one way. But its theoretically possible that they might

be broken by future Cryptanalysts.


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Nonce

One of the more recognizable examples of

a nonce is an Initialization Vector (IV), a

random bit string that is the same length

as the block size and is XORed with themessage.

IVs are used to create Unique Cipher

Text every time the same message isencrypted using the same key.


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Zero-Knowledge Proof


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Work Function

Measuring the strength of a cryptography

system by measuring the effort in terms of

cost and/or time using a Work Function.

Spend no more effort to protect an asset

than it warrants, but Be Sure To Provide

Sufficient Protection.

Thus, if information loses its value over time,

the work function needs to be only large

enough to ensure protection until the value of

the data is gone.


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Chiper

Ciphers are always meant to Hide The

True Meaning Of A Message.

They use a variety of techniques to alter

and/or re-arrange the characters or bits of

a message to achieve confidentiality.

Ciphers Convertmessages from plain textto cipher text on a bit basis, character basis,or

block basis.


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Chiper:

Transposition Transposition ciphers use an encryption

algorithm to rearrange the letters of a

plain-text message, forming the cipher-text

message.

The decryption algorithm simply reverses

the encryption transformation to retrieve

the original message.


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Chiper:

TranspositionIn this example, were attempting to encrypt

the message The fighters will strike the

enemy bases at noon using the secret

key attacker.

Chipertext


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Chiper:

Block Chiper Block ciphers operate

on chunks or

blocks, of a message

and apply theencryption algorithm to

an entire message

block at the same time. The transposition

ciphers are examples of

block ciphers.


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Chiper:

Stream Chiper Stream ciphers are ciphers that operate on

each character or bit of a message (or

data stream) one character/bit at a time.

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