Cryptography is the study of secure communication techniques. The document provides a high-level overview of basic cryptography concepts including its history, objectives, terminology, and types (symmetric, asymmetric, hash functions). Symmetric cryptography uses a single secret key for encryption and decryption while asymmetric cryptography uses two keys: a public key for encryption and a private key for decryption. Popular symmetric algorithms include AES and RSA. Hash functions like MD5 and SHA are used to verify message integrity. Quantum computing may improve applications like cancer treatment, traffic optimization, and weather forecasting by solving complex optimization problems.

1. Basic Cryptography
Assoc. Prof. Ts. Dr. Madihah Mohd Saudi
Faculty of Science & Technology, USIM

2. CONTENTS
• Introduction
• History of Cryptography
• Objectives
• Basic Terminology in Cryptography
• Types of Cryptography
• Symmetric
• Asymmetric
• Hash Function

3. Introduction
• Cryptography:
• the study of secure communications techniques that allow
only the sender & intended recipient of a message to view
its contents.
• derived from the Greek word kryptos, which means hidden
Phil Zimmermann
• Cryptography is the science of using mathematics to
encrypt & decrypt data.
Bruce Schneier
• Cryptography is the art & science of keeping messages
secure.

4. History of Cryptography
• The roots of cryptography are found in Egyptian & Roman
civilizations.
• Hieroglyph – The Oldest Cryptographic Technique
• Some 4000 years ago, Egyptians used to communicate by messages
written in hieroglyph.
• This code was the secret known only to the scribes who used to transmit
messages on behalf of the kings.
• Caesar Shift Cipher, relies on shifting the letters of a message by an agreed number (3
was a common choice), the recipient of this message would then shift the letters back by
the same number & obtain the original message.
• The Caesar cipher is named after Julius Caesar , who used it with a shift of three to
protect messages of military significance.

5. Caesar Shift Cipher
• Plaintext: basic cryptography
• Ciphertext: edvlf fubswrjudskb

6. Authenticity ensures the
sender & recipient can
verify each other’s
identities & the destination
of the message.
Objectives
Authenticity
Non-repudiation
Confidentiality
Integrity
Non-repudiation means the
sender of the message cannot
backtrack in the future & deny
their reasons for sending or
creating the message.
Confidentiality ensures
that only the intended
recipient can decrypt the
message & read its
contents.
Integrity focuses on the
ability to be certain that
the information contained
within the message
cannot be modified while
in storage or transit.

7. Basic Terminology in Cryptography
Plaintext
The original message
Ciphertext
The coded message
Enciphering or
encryption
Process of converting
from plaintext to
ciphertext
Deciphering or
decryption
Restoring the plaintext
from the ciphertext
Cryptography
Study of encryption
Cryptographic system or
cipher
Schemes used for
encryption
Cryptanalysis
Techniques used for
deciphering a message
without any knowledge
of the enciphering details
Cryptology
Areas of cryptography &
cryptanalysis together

8. Uses two different key to encrypt
& decrypt the message
The message is encrypted by
using a key & the same key is used
to decrypt the message
Types of Cryptography
Symmetric Key
Cryptography
Asymmetric Key
Cryptography

9. Symmetric Key Cryptography

10. Symmetric Key Cryptography
Simplest kind of encryption -
only one secret key to cipher
& decipher information.
It uses a secret key that can
either be a number, a word or
a string of random letters. It is
a blended with the plain text
of a message to change the
content in a particular way.
The sender & the recipient
should know the secret key
that is used to encrypt &
decrypt all the messages.
The main disadvantage : all
parties involved must
exchange the key used to
encrypt the data before they
can decrypt it.
Example:
Blowfish, AES( AES-128, AES-
192, & AES-256), RC4, DES,
RC5, & RC6

11. Symmetric Key
Cryptography
Classical
Cryptography
Transposition
Ciphers
Substitution
Cipher
Modern
Cryptography
Stream Cipher
Block Cipher

12. Classical Cryptography
• Transposition Ciphers
• method of encryption by
which the positions held by
units of plaintext (which are
commonly characters or
groups of characters) are
shifted according to a regular
system, so that the
ciphertext constitutes a
permutation of the plaintext

13. Classical Cryptography
• Substitution Ciphers
• Method of encryption by which units of plaintext are replaced with ciphertext,
according to a fixed system; the “units” may be single letters (the most common),
pairs of letters, triplets of letters, mixtures of the above, and so forth.

14. Modern Cryptography
• Stream Cipher
• Symmetric or secret-key
encryption algorithm
that encrypts a single bit
at a time. With a Stream
Cipher, the same
plaintext bit or byte will
encrypt to a different bit
or byte every time it is
encrypted.

15. Modern Cryptography
• Block Cipher
• An encryption method
that applies a
deterministic algorithm
along with a symmetric
key to encrypt a block of
text, rather than
encrypting one bit at a
time as in stream
ciphers Example: A common block cipher, AES, encrypts 128-bit blocks with a key of
predetermined length: 128, 192, or 256 bits. Block ciphers are pseudorandom
permutation (PRP) families that operate on the fixed size block of bits. PRPs are
functions that cannot be differentiated from completely random permutations and
thus, are considered reliable until proven unreliable.

16. Advanced Encryption Standard (AES)
• The features of AES are :
• Symmetric key symmetric block
cipher
• 128-bit data, 128/192/256-bit
keys
• Stronger and faster than Triple-
DES
• Provide full specification and
design details
• Software implementable in C and
Java

17. Asymmetric Key Cryptography

18. Asymmetric Key Cryptography
• Also known as public key cryptography
• Asymmetric encryption uses two keys to encrypt a plain text. Secret keys are
exchanged over the Internet or a large network. It ensures that malicious persons
do not misuse the keys.
• It is important to note that anyone with a secret key can decrypt the message &
therefore asymmetric encryption uses two related keys to boosting security. A
public key is made freely available to anyone who might want to send you a
message. The second private key is kept a secret so that you can only know.
• Asymmetric encryption is mostly used in day-to-day communication channels,
especially over the Internet. Popular asymmetric key encryption algorithm :
EIGamal, RSA, DSA, Elliptic curve techniques, PKCS.

19. RSA Algorithm
• Most widely used
form of public key
encryption
• RSA stands for
Rivest, Shamir, and
Adelman, inventors
of this technique
• Both public and
private key are
interchangeable
• Variable Key Size
(512, 1024, or 2048
bits)

20. Differences Between Symmetric & Asymmetric Encryption
Key Differences Symmetric Encryption Asymmetric Encryption
Size of cipher text Smaller cipher text compares to original plain text file. Larger cipher text compares to original plain text file.
Data size Used to transmit big data. Used to transmit small data.
Resource Utilization Works on low usage of resources. Requires high consumption of resources.
Key Lengths 128 or 256-bit key size. RSA 2048-bit or higher key size.
Security Less secured due to use a single key for encryption. Much safer as two keys are involved in encryption & decryption.
Number of keys Uses a single key for encryption & decryption. Uses two keys for encryption & decryption
Techniques It is an old technique. It is a modern encryption technique.
Confidentiality
A single key for encryption & decryption has chances of key
compromised.
Two keys separately made for encryption & decryption that
removes the need to share a key.
Speed Symmetric encryption is fast technique Asymmetric encryption is slower in terms of speed.
Algorithms RC4, AES, DES, 3DES, & QUAD. RSA, Diffie-Hellman, ECC algorithms.

21. Hash Function
• A cryptographic hash function
• is a hash function that takes an
arbitrary block of data & returns a
fixed-size bit string, the cryptographic
hash value, such that any (accidental or
intentional) change to the data will
(with very high probability) change the
hash value.
• The data to be encoded are often called the
message, & the hash value is sometimes
called the message digest or simply digest.
• Popular Hash Functions: Message Digest
(MD) & Secure Hash Function (SHA)

22. Popular Hash Functions
Message
Digest
(MD)
comprises of hash functions MD2, MD4, MD5
and MD6
MD5 digests have been widely used in the
software world to provide assurance about
integrity of transferred file.
For example, file servers often provide a pre-
computed MD5 checksum for the files, so that
a user can compare the checksum of the
downloaded file to it.
In 2004, collisions were found in MD5.. This
collision attack resulted in compromised MD5
and hence it is no longer recommended for
use.
Secure
Hash
Function
(SHA)
comprise of four SHA algorithms; SHA-0, SHA-1, SHA-
2, and SHA-3
The original version is SHA-0, a 160-bit hash function,
SHA-1 is the most widely used of the existing SHA hash
functions. It is employed in several widely used
applications and protocols including Secure Socket
Layer (SSL) security.
SHA-2 is a strong hash function. Though significantly
different, its basic design is still follows design of SHA-
1
In Oct 2012, the NIST chose the Keccak algorithm as
the new SHA-3 standard. Keccak offers many benefits,
such as efficient performance and good resistance for
attacks.

23. Quantum Computing

24. -Quantum theory: focuses on phenomenon of energy & quantum level.
-Quantum computing:
• uses the principles of quantum theory to develop computer technologies.
• encompasses quantum cryptography & quantum communication.
• enormous power-> the capability to be in multiple states at the same time
and perform tasks using all possible permutations simultaneously.
-Applications of Quantum Computing:
• Improving Cancer Treatment
• Optimizing Traffic Flow
• Portfolio Optimization
• Simulate Molecules
• Make AI More Human-like
• Forecasting Weather
• Customized Advertising

25. Improving Cancer
Treatment
• 2015: the researchers at the Roswell Park Cancer Institute proposed a new way to
optimize the radiation beams that uses quantum annealing computers.
• 2017: Volkswagen tried to address the issue of traffic by tackling the traffic itself.
• QUBO-Quadratic Unconstraint Binary Optimization technique along with the
quantum annealing computers -> to find the optimal route for a certain number of
cars in addition to all the possible routes in consideration.
• Tested about 10000 taxis in Beijing-> to prove how this method optimizes traffic
faster > classical computers.
Optimizing Traffic Flow

26. Portfolio
Optimization
• Deals with selecting the best asset to invest in, which balances the risk with the
expected returns.
• Quantum annealing -> help answer these in a jiffy.
• Quantum computers->simulate small molecules like beryllium hydride (BeH2).
• Even if this looks small now, the fact that a 7-qubit chip simulated this molecule
holds significance as had there been more qubits at our disposal, it would’ve been
possible to simulate bigger molecules.
• The processing capabilities of a quantum computer increase with an increase in the
number of qubits
Simulate Molecules

27. Make AI More
Human-like
• Quantum computing -> matrices are used to determine the states of the qubits.
• Essentially, any computational process performed on the neural networks-> similar to applying
transformational quantum gates on qubits (a quantum gate is a basic circuit operating on a small
number of qubits).
• This makes quantum computers a perfect fit to implement AI.
• 2017, a researcher from Russia-> proposing the possibility of quantum computers predicting the
weather more accurately as compared to classical computers.
• A major issue with predicting the weather correctly is the involvement of a large amount of data.
• With the help of the Dynamic Quantum Clustering (DQC) methodology, quantum computers are
expected to speed up the data processing to give us more accurate weather forecasts.
Forecasting Weather

28. Customized
Advertising
• Recruit Communications:
• relevancy of ads.
• explained how companies-> use
quantum annealing to reach their
audience with relevant ads so as to
increase the CTR (Click Through
Rate).
• Improved mobile data coverage
• More human-like AI, such as
Google AI, which is developing
quantum algorithms to drastically
improve machine learning