Cryptography and Network Security Public Key Cryptography and RSA.
Cryptography -- ps.ppt
Transcript of 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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Cryptography Concept
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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Cryptography Concept
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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Cryptography Concept
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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Cryptography Concept
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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Cryptography Mathematics:
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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Cryptography Mathematics:
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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Cryptography Mathematics:
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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Cryptography Mathematics:
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.