This document provides an overview of cryptography. It defines cryptography as a method of storing and transmitting data in a way that only the transmitter and receiver can access the information. The document then discusses the history of cryptography, including classic ciphers like the Caesar cipher and modern techniques like symmetric and asymmetric cryptography. It describes how symmetric cryptography uses a single key for encryption and decryption while asymmetric cryptography uses public-private key pairs. The document outlines some examples of symmetric and asymmetric algorithms and analyzes the advantages and disadvantages of each approach. Finally, it discusses some applications of cryptography like ATM PINs, encrypted drives, digital signatures, and time stamping.

1. CRYPTOGRAPHY
Digital Communication

2. Group Members
• Muhammad Shoaib Saleem (13-TE-32)
• M. KhurramTufail (13-TE-88)
• Anik Ahmed (13-TE-66)

3. Cryptography
It is the combination of two Greek words
1. Kryptos 2.Graphien
Secret Studying

4. Definition
Cryptography is a method of storing
and transmitting data in a particular
form so that only transmitter and
receiver can extract useful
information.
One of the ancient cipher machines used
inWorldWar II
Cryptography is about constructing
and analyzing protocols that prevent
third parties from reading private
messages or other useful
information

5. Terminology
• It is exclusively referred to encryption i.e. changing useful information to
unintelligible text.
Useful information Plaintext & Unintelligible text cyphertext
• Cipher is a pair of algorithm for doing encryption and decryption.
• In cryptography, Key is a piece of information that determines the
functional output of cryptographic algorithm.
• Cryptosystem is the ordered list of elements of finite possible plaintexts,
finite possible cyphertexts, finite possible keys, and the encryption and
decryption algorithms which correspond to each key.

6. Cont.
• In conversational use, the term code is used for concealment of meaning. In
cryptography, meaningful word or phrase is replaced by some code words.
e.g. "wallaby" replaces "attack at dawn“.
• Cryptanalysis is the study of how to crack encryption algorithms or their
implementation.
Here, k=3

7. History of Cryptography
oClassic Cryptography
• Transposition ciphers
• Substitution ciphers
• Caesar ciphers
oModern Cryptography
• Symmetric cryptography
• Asymmetric Cryptography

8. Classic Cryptography
Scytale: Ancient CipherTool ForTransposition Cipher French Cipher Machine in the Shape of Book

9. Modern Cryptography
• Symmetric Cryptography:
A single key is used both for encryption of plaintext and
decryption of ciphertext.
• Asymmetric Cryptography:
Pairs of keys are used; public keys paired with private key

10. Symmetric Cryptography

11. Types of Symmetric Cryptography
Stream Ciphers
• Mixes plaintext with key stream.
• Good for real-time services.
Block Ciphers
• Substitution and transposition ciphers are
used.
• e.g. DES,AES

12. Advantages of Symmetric Cryptography
• Extremely secure
o U.S.Government-designatedAdvanced Encryption Standard.When you use it with its
most secure 256-bit key length, it would take about a billion years for a 10 petaflop
computer to guess the key through a brute-force attack.
• Relatively fast
o Reason behind its being faster is key that is used for decryption of data is already
known as it is used for encryption before. So that many faster disk drives used this
cryptography.

13. Disadvantages of Symmetric Cryptography
• Sharing the Key
• Strong key management system is required along with the safe way to get the key to
the other party.
• More Damage if Compromised
• As same key is used so it is danger for both communicants to being compromised if key
is known to any third party.

14. Asymmetric Cryptography
It is also called public key cryptosystem.

15. Types of AsymmetricCryptography
Ravist-Shamir-Adleman
• This algorithm uses prime numbers and
factorization as the basis for generating
encryption keys.
• While generating public and private keys, the
RSA algorithm takes two large prime numbers
and multiplies them.
Digital Signature Algorithm
• This algorithm provides a verification
mechanism through asymmetrical encryption.
• The private and public keys are linked in it. But
only the private key can decrypt the signature.
Secure Sockets Layer
• The Secure Sockets Layer itself does not
represent an asymmetrical encryption
algorithm. Rather, as part of its protocol
• it employs various symmetric and asymmetric
algorithms to encrypt data.
• SSL works by negotiating an encryption
method between two computers, and then
applying that encryption

16. Advantages of Asymmetric Cryptography
• Key Security
• Decryption is done by the private key of receiver which is not even known to sender. So
key security is never be compromised
• IdentityVerification
• Any data that is encrypted with a person's public key can only be encrypted with their
private key.
• Less risk of compromising
• the hacker will only have access to half of the conversation.

17. Cont.
• SecureAlgorithms
• The Rivest-Shamir-Adleman algorithm, was first developed in the 1980s, it remains
unbroken. 6*1024 years are required to do hacking of that algorithms with a 2.2 GHz
multi-core processor.

18. Disadvantages of Asymmetric Cryptography
• Speed
• The encryption and decryption processes have to work with two different keys, each
related to each other by a complex mathematical process involving prime number
factorization.
• Uses up more computer resources
• It requires a lot more computer supplies compared to single-key encryption.

19. Applications
• The personal identity number (PIN) that must be entered into an automated
teller machine (ATM)
• Cryptography is used for lock up the computers or hard drives.
• Authentication and digital signatures are a very important application of
public-key cryptography.
• Time stamping is a technique that can certify that a certain electronic
document or communication existed or was delivered at a certain time.

20. ThankYou
Any Questions?