Introduction to Cryptography

Introduction to
Cryptography
-Afif

Contents
• Introduction
• History
• Terminology
• Cryptography Methods
• Difference between Methods
• Application

Introduction
Cryptography:
Cryptography is a method of storing and transmitting data in a
particular form so that only those for whom it is intended can read and
process it. Cryptography is closely related to the disciplines
of cryptology and cryptanalysis. Cryptography includes techniques such
as microdots, merging words with images, and other ways to hide
information in storage or transit.

German Lorenz cipher machine, used in World War II to
encrypt very-high-level general staff messages.

History
BCE: Spartan use of scytale, the Egyptians develop hieroglyphic writing
and Notable Roman ciphers such as the Caesar cipher.
1-1799: Leon Battista Alberti invents polyalphabetic cipher, also known
first mechanical cipher machine.
1800-1899: Joseph Henry builds an electric. In Crimean War, Charles
Babbage broke Vigenère's autokey cipher (the 'unbreakable cipher' of
the time).

1900-1949: First break of German Army Enigma by Marian Rejewski in
Poland.
1950-1999: Charles Bennett and Gilles Brassard design the
first quantum cryptography protocol, BB84.
2000 to present: Microsoft and its allies vow to end "full
disclosure" of security vulnerabilities by replacing it
with "responsible" disclosure guidelines.

Classic cryptography
The Greek’s idea on cryptography was to
wrap a tape around a stick, and then
write the message on the wound tape.
When the tape was unwound, the
writing would be meaningless. The
receiver of the message would of course
have a stick of the same diameter and
use it to decipher the message.
Reconstructed ancient Greek
scytale, an early cipher device.

Computer era
Cryptanalysis of the new mechanical devices
proved to be both difficult and laborious. Just as
the development of digital computers and
electronics helped in cryptanalysis, it made
possible much more complex ciphers.
Furthermore, computers allowed for the
encryption of any kind of data representable in
any binary format, unlike classical ciphers which
only encrypted written language texts.
An example of simple cryptography

Terminology
Plaintext:
Message that is going to be transmitted or stored is plain text. Anyone
can read plaintext.
Encryption:
The method by which we can hide the actual meaning of plaintext is
called Encryption.

Cipher text:
The result of encryption which results in unreadable gibberish is called
Cipher text.
Decryption:
The method by which the original meaning of cipher text can be
recovered is called Decryption. Simply the process of converting Cipher
text to plaintext is called Decryption.

Key:
Key is the secret piece of information which is used for encryption and
decryption in Cryptography.

Method of Encryption and Decryption

 Some more terms:
Cryptanalysis:
The science of retrieving the plain text from cipher without knowing
the key.
Cryptanalysts:
The people who practice cryptanalysis are called Cryptanalyst.

Cryptosystem:
The combination of algorithm, key, and key management functions
used to perform cryptographic operations.

 Caesar Cipher
The Caesar cipher, also known as a shift cipher, is one of the simplest
forms of encryption. It is a substitution cipher where each letter in the
original message (called the plaintext) is replaced with a letter
corresponding to a certain number of letters up or down in the
alphabet.

Caesar Cipher with shifting value ‘3’

We love
Discrete
Mathematics
Zh oryh
Glvfuhwh
Pdwkhpdwlfv
We love
Discrete
Mathematics
Right shift
of
3
Left shift
of
3
Plaintext Cipher Plaintext

Cryptography Methods
Symmetric Key:
With Symmetric key Cryptography, a single key is used for both
encryption and decryption. In this figure we can see that the sender
uses the key to encrypt the plain text and send the cipher text to the
receiver. The receiver applies the same key to decrypt the message and
recover the plain text because a single key is used for both function.
Symmetric key Cryptography is also called secret key Cryptography.
With this from of Cryptography, it is obvious that the key must be
known to both the sender and the receiver.

Visualization of Symmetric key Cryptography

Asymmetric Key:
Asymmetric cryptography was first publicly described by martin
Hellman and his student Whitfield Diffie in 1976. There are two
different keys are used for encryption and decryption. One key is used
to encrypt the plaintext and the other key is used to decrypt the cipher
text the important point is that it doesn’t matter which key is applied
first but the both key is required for the work. Every user has both a
public key and a private key. The private key is kept secret at all times,
but the public key may be freely distributed.

Visualization of Asymmetric key Cryptography

Symmetric Cryptography
Examples of encryption:
DES, 3DES, AES and RC4.

Asymmetric Cryptography
Examples of encryption:
The most common asymmetric encryption
algorithm is RSA

Applications
1. ATM
2. Email-Passwords
3. E-Payment
4. E-Commerce
5. Electronic Voting
6. Defence Services
7. Securing Data
8. Access Control

Introduction to Cryptography

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