It is cryptography for hc

1. AGENDA
Lecturer : Ajmal Azizi 1
Contents
A. What is Cryptography?
B. Goals of Cryptography
C. Terminologies of Cryptography
D. Symmetric Cryptography
E. Asymmetric Cryptography
D. Digital Signature
E. Attack on Cryptography

2. Cryptography is a way to store and transmit
data so only the intended recipient can read or
process it. Modern cryptography uses
computationally secure algorithms to make
sure that cyber criminals cannot easily
compromise protected information.
Lecturer : Ajmal Azizi 2
What is Cryptography

3. • Security practitioners use cryptographic systems to meet
four fundamental goals:
1. Confidentiality
2. Integrity
3. Authentication
4. nonrepudiation.
Achieving each of these goals requires the satisfaction of a
number of design requirements, and not all cryptosystems are
intended to achieve all four goals.
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Goals of Cryptography

4. • Plaintext Message
• Cipher Test Message
• Algorithm
• Encryption
• Decryption
• Key
• Cryptanalysis
• Cryptosystem
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Terminologies of
Cryptography

5. 1. Transposition ciphers use an encryption algorithm
to rearrange the letters of a plaintext message,
forming the cipher text message. The decryption
algorithm simply reverses the encryption
transformation to retrieve the original Message.
Lecturer : Ajmal Azizi 5
Several common ciphers

6. • In the following example, we’re attempting to encrypt the message
“The fighters will strike the enemy bases at noon” using the secret
key attacker.
• Our first step is to take the letters of the keyword and number them in
alphabetical order. The first appearance of the letter A receives the
value 1; the second appearance is numbered 2. The next letter in
sequence, C, is numbered 3, and so on. This results in the following
sequence
Lecturer : Ajmal Azizi 6
1. Transposition ciphers

7. Next, the letters of the message are written in order underneath the letters of the
keyword:
A T T A C K E R
1 7 8 2 3 5 4 6
T H E F I G H T
E R S W I L L S
T R I K E T H E
E N E M Y B A S
E S A T N O O N
Finally, the sender enciphers the message by reading down each column; the
order in which the columns are read corresponds to the numbers assigned in the
first step. This produces the following cipher text:
T E T E E F W K M T I I E Y N H L H A O G L T B O T S E S N H R R N S E S I E A
Lecturer : Ajmal Azizi 7
1. Transposition ciphers

8. Substitution ciphers use the encryption algorithm to replace
each character or bit of the plaintext message with a different
character. One of the earliest known substitution ciphers was
used by Julius Caesar to communicate with Cicero in Rome
while he was conquering Europe.
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Substitution Ciphers

9. • Here’s an example of the Caesar cipher in action. The first
line contains the original sentence, and the second line
shows what the sentence looks like when it is encrypted
using the Caesar cipher.
THE DIE HAS BEEN CAST
WKH GLH KDV EHHQ FDVW
• To decrypt the message, you simply shift each letter three
places to the left.
Lecturer : Ajmal Azizi 9
Substitution Ciphers

10. • Block ciphers operate on “chunks,” or blocks, of a message and apply
the encryption algorithm to an entire message block at the same time.
The transposition ciphers are examples of block ciphers.
• The simple algorithm used in the challenge-response algorithm takes
an entire word and reverses its letters.
• The more complicated columnar transposition cipher works on an
entire message (or a piece of a message) and encrypts it using the
transposition algorithm and a secret keyword. Most modern
encryption algorithms implement some type of block cipher.
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Block ciphers

11. • Stream ciphers operate on one character or bit of a
message (or data stream) at a time.
• The Caesar cipher is an example of a stream cipher.
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Stream Ciphers

12. • Modern cryptosystems use computationally complex algorithms and
long cryptographic keys to meet the cryptographic goals of
confidentiality, integrity, authentication, and nonrepudiation.
• The following sections cover the roles cryptographic keys play in the
world of data security and examine three types of algorithms
commonly used today: symmetric encryption algorithms, asymmetric
encryption algorithms, and hashing algorithms.
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Modern Cryptography

13. • Symmetric key algorithms rely on a “shared secret”
encryption key that is distributed to all members who
participate in the communications.
• This key is used by all parties to both encrypt and decrypt
messages, so the sender and the receiver both possess a
copy of the shared key. The sender encrypts with the shared
secret key and the receiver decrypts with it.
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Symmetric Key Algorithms

14. Lecturer : Ajmal Azizi 14
Symmetric Key
Cryptography

15. Key distribution is a major problem - Parties must have a secure method of
exchanging the secret key before establishing communications with a symmetric key
protocol.
Symmetric key cryptography does not implement nonrepudiation - Because any
communicating party can encrypt and decrypt messages with the shared secret key,
there is no way to prove where a given message originated.
The algorithm is not scalable- It is extremely difficult for large groups to
communicate using symmetric key cryptography.
Keys must be regenerated often- Each time a participant leaves the group, all keys
known by that participant must be discarded
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Symmetric key cryptography has
several weaknesses:

16. • The major strength of symmetric key cryptography is the
great speed at which it can operate. Symmetric key
encryption is very fast, often 1,000 to 10,000 times faster
than asymmetric algorithms.
• By nature of the mathematics involved, symmetric key
cryptography also naturally lends itself to hardware
implementations, creating the opportunity for even higher-
speed operations and bulk encryption tasks.
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The major strength of
symmetric key

17. The U.S. government published the Data Encryption Standard in 1977
as a proposed standard cryptosystem for all government
communications. Because of flaws in the algorithm, cryptographers and
the federal government no longer consider DES secure.
3DES (Triple DES): Digital Encryption Standard (DES) is a symmetric
block cipher with 64-bit block size that uses a 56-bit key. It takes a 64-bit
block of plaintext as input and outputs a 64-bit block of ciphertext. It
always operates on blocks of equal size.
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Some of the common encryption standards that use symmetric
encryption include the following:

18. • The International Data Encryption Algorithm (IDEA) uses 64-bit
blocks and 128-bit keys.
• IDEA performs eight rounds of transformations on each of the 16
blocks that results from dividing each 64-bit block. IDEA was the
replacement for DES, and now PGP (Pretty Good Privacy) uses it.
• PGP is a program that provides privacy and authentication for data
communication. GNU Privacy Guard (GPG) is a licensed, free version
of PGP.
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IDEA

19. Ron Rivest, of Rivest-Shamir-Adleman (RSA) Data Security, created a
series of symmetric ciphers over the years known as the Rivest Ciphers
(RC) family of algorithms.
Several of these, RC4, RC5, and RC6, have particular importance today.
Rivest Cipher 4 (RC4): RC4 is a stream cipher developed by Rivest in
1987 and very widely used during the decades that followed. It uses a
single round of encryption and allows the use of variable-length keys
ranging from 40 bits to 2,048 bits.
RC4’s adoption was widespread because it was integrated into the Wired
Equivalent Privacy (WEP), Wi-Fi Protected Access (WPA), Secure
Sockets Layer (SSL), and Transport Layer Security (TLS) protocols.
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Rivest Ciphers

20. The Advanced Encryption Standard (AES) has a fixed
block size of 128-bits with a key size of 128, 192, or
256 bits. The National Institute of Standards and
Technology (NIST) approved the AES algorithm in
December 2001. The U.S. government uses AES to
protect classified information.
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AES

21. As previously mentioned, one of the major problems
underlying symmetric encryption algorithms is the
secure distribution of the secret keys required to
operate the algorithms. The three main methods used
to exchange secret keys securely are offline
distribution, public key encryption, and the Diffie–
Hellman key exchange algorithm.
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Distribution of Symmetric
Keys

22. • Offline Distribution : The most technically simple (but physically
inconvenient) method involves the physical exchange of key material.
One party provides the other party with a sheet of paper or piece of
storage media containing the secret key.
• Public Key Encryption : Many communicators want to obtain the
speed benefits of secret key encryption without the hassles of key
distribution. For this reason, many people use public key encryption to
set up an initial communications link.
• Diffie–Hellman In some cases, neither public key encryption nor
offline distribution is sufficient. Two parties might need to
communicate with each other, but they have no physical means to
exchange key material, and there is no public key infrastructure in
place to facilitate the exchange of secret keys. In situations like this,
key exchange algorithms like the Diffie–Hellman algorithm prove to
be extremely useful.
Lecturer : Ajmal Azizi 22

23. • Asymmetric key algorithms provide a solution to the weaknesses of
symmetric key encryption.
• Public key algorithms are the most common example of asymmetric
algorithms. In these systems, each user has two keys: a public key,
which is shared with all users, and a private key, which is kept secret
and known only to the user.
• But here’s a twist: opposite and related keys must be used in tandem
to encrypt and decrypt.
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Asymmetric key algorithms

24. Lecturer : Ajmal Azizi 24
Asymmetric key
algorithms…

25. • Asymmetric key algorithms also provide support for digital
signature technology. Basically, if Bob wants to assure other users
that a message with his name on it was actually sent by him, he first
creates a message digest by using a hashing algorithm.
• Bob then encrypts that digest using his private key. Any user who
wants to verify the signature simply decrypts the message digest using
Bob’s public key and then verifies that the decrypted message digest
is accurate.
Lecturer : Ajmal Azizi 25
Asymmetric key
algorithms…

26. • The addition of new users requires the generation of only one public-private
key pair.
• Users can be removed far more easily from asymmetric systems.
• Key regeneration is required only when a user’s private key is compromised.
• Asymmetric key encryption can provide integrity, authentication,
and nonrepudiation.
• Key distribution is a simple process.
• No preexisting communication link needs to exist.
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The major strengths of asymmetric key
cryptography:

27. • The major weakness of public key cryptography is its slow
speed of operation. For this reason, many applications that
require the secure transmission of large amounts of data use
public key cryptography to establish a connection and then
exchange a symmetric secret key.
• The remainder of the session then uses symmetric
cryptography. This approach of combining symmetric and
asymmetric cryptography is known as hybrid cryptography.
Lecturer : Ajmal Azizi 27
Weakness of Asymmetric

28. • The most famous public key cryptosystem is named after its
creators. In 1977, Ronald Rivest, Adi Shamir, and
Leonard Adleman proposed the RSA public key algorithm,
which remains a worldwide standard today.
• They patented their algorithm and formed a Commercial
venture known as RSA Security to develop mainstream
implementations of their security technology. Today, the
RSA algorithm has been released into the public domain and
is widely used for secure communication.
Lecturer : Ajmal Azizi 28
RSA

29. Diffie-Hellman - Provides an electronic exchange method to share the
secret key. Secure protocols, such as Secure Sockets Layer (SSL),
Transport Layer Security (TLS), Secure Shell (SSH), and Internet
Protocol Security (IPsec), use Diffie-Hellman.
ElGamal - uses the U.S. government standard for digital signatures. This
algorithm is free for use because no one holds the patent.
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Diffie-Hellman

30. Lecturer : Ajmal Azizi 30

31. • Hash functions have a very simple purpose—they take a potentially long
message and generate a unique output value derived from the content of the
message.
• This value is commonly referred to as the message digest. Message digests
can be generated by the sender of a message and transmitted to the recipient
along with the full message for two reasons.
• First, the recipient can use the same hash function to recomputed the
message digest from the full message. They can then compare the computed
message digest to the transmitted one to ensure that the message sent by the
originator is the same one received by the recipient.
• Second, the message digest can be used to implement a digital signature
algorithm.
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Hash functions

32. • The input can be of any length.
• The output has a fixed length.
• The hash function is relatively easy to compute for any
input.
• The hash function is one-way (meaning that it is extremely
hard to determine the input when provided with the output).
• The hash function is collision resistant (meaning that it is
extremely hard to find two messages that produce the same
hash value).
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According to RSA Security, there are five basic requirements for a
cryptographic hash function

33. • SHA The Secure Hash Algorithm (SHA) and its successors, SHA-1,
SHA-2, and SHA-3, are government standard hash functions
promoted by the National Institute of Standards and Technology
(NIST).
• SHA-1 takes an input of virtually any length (in reality, there is an
upper bound of approximately 2,097,152 terabytes on the algorithm)
and produces a 160-bit message digest.
• Cryptanalytic attacks demonstrated that there are weaknesses in the
SHA-1 algorithm, and therefore, NIST deprecated SHA-1 and no
longer recommends its use for any purpose, including digital
signatures and digital certificates. Web browsers dropped support for
SHA-1 in 2017. As a replacement, NIST announced the SHA-2
standard,
Lecturer : Ajmal Azizi 33
SHA

34. • The Message Digest 2 (MD2) hash algorithm was developed by
Ronald Rivest (the same Rivest of Rivest, Shamir, and Adleman fame)
in 1989 to provide a secure hash function for 8-bit processors.
• In 1990, Rivest enhanced his message digest algorithm to support 32-
bit processors and increase the level of security with a version called
MD4. In 1991, Rivest released the next version of his message digest
algorithm, which he called MD5.
• MD5 implements additional security features that reduce the speed of
message digest production significantly. Unfortunately, cryptanalytic
attacks demonstrated that the MD5 protocol is subject to collisions,
preventing its use for ensuring message integrity.
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MD5

35. • Once you have chosen a cryptographically sound hash function and
cryptographic algorithm, you can use it to implement a digital
signature system.
• Digital signature infrastructures have two distinct goals:
1. Digitally signed messages assure the recipient that the message truly
came from the claimed sender. They enforce nonrepudiation
2. Digitally signed messages assure the recipient that the message was
not altered while in transit between the sender and recipient.
• Digital signature algorithms rely on a combination of the two major
concepts already covered in this chapter—public key cryptography
and hashing functions
Lecturer : Ajmal Azizi 35
Digital Signatures

36. If Alice wants to digitally sign a message she’s
sending to Bob, she performs the following
actions:
1. Alice generates a message digest (i.e., hash) of the original plaintext
message using one of the cryptographically sound hashing algorithms,
such as SHA2-512.
2. Alice then encrypts only the message digest using her private key.
This encrypted message digest is the digital signature.
3. Alice appends the signed message digest to the plaintext message.
4. Alice transmits the appended message to Bob
Lecturer : Ajmal Azizi 36

37. 1. Bob decrypts the digital signature using Alice’s public key.
2. Bob uses the same hashing function to create a message digest of the
full plaintext message received from Alice.
3. Bob then compares the decrypted message digest he received from
Alice with the message digest he computed himself. If the two
digests match, he can be assured that the message he received was
sent by Alice.
Lecturer : Ajmal Azizi 37
When Bob receives the digitally signed message, he reverses the
procedure, as follows:

38. • Digital certificates provide communicating parties with the assurance
that the people they are communicating with truly are who they claim
to be.
• Digital certificates are essentially endorsed copies of an individual’s
public key. When users verify that a certificate was signed by a trusted
certificate authority (CA), they know that the public key is legitimate.
• Digital certificates contain specific identifying information, and their
construction is governed by an international standard
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Certificates

39. • Steganography is the art of using cryptographic techniques to embed
secret messages within another message.
• Steganography algorithms work by making alterations to the least
significant bits of the many bits that make up image files.
• The changes are so minor that there is no appreciable effect on the
viewed image.
• This technique allows communicating parties to conceal messages in
plain sight—for example, they might embed a secret message within
an illustration on an otherwise innocent web page
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Steganography
and Watermarking

40. Cryptography plays a central role in many emerging areas of
cybersecurity and technology.
Let’s take a look at a few of these concepts:
• the block chain
• lightweight cryptography
• homomorphic encryption
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Emerging Applications

41. • Analytic Attack
• Implementation Attack
• Statistical Attack
• Brute-Force Attack
• Fault Injection Attack
• Side-Channel Attack
• Timing Attack
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Cryptographic Attacks

42. THE END
Lecturer : Ajmal Azizi 42