Cryptography

‘’ The Science of Encryption ’’

• What is cryptography ?

• Why cryptography is important ?

Contents• The purpose of cryptography• History of cryptography and cryptanalysis• Modern cryptography(Types of Algorithms)

- Secret Key Cryptography- Hash Functions- Public Key Cryptography- Why Three Encryption Techniques?- The Significance of Passwords & Password Security

• Conclusion

Science of writing in secret code

THE PURPOSE OF CRYPTOGRAPHY Computer communications Data transfer and telecommunicationSpecific security requirements for communication:

Authentication:

Privacy/confidentiality:

Integrity:

Non-repudiation:

The history of cryptography can be divided into two parts:

(1) From ancient civilizations to the 19th century and the first part of the 20th century,

(2) Use of encrypting electro-mechanical machines, around the period of the WW II.

HISTORY OF CRYPTOGRAPHY

Cryptography:

Greek κρυπτός, kryptos,

"hidden, secret"

HISTORY OF CRYPTOGRAPHY

Cryptography was used in three kinds of contexts in ancient times :

Private communications

Art and religion

Military and diplomatic use

Here we have three types of algorithms that we can talk about:

MODERN CRYPTOGHRAPHY

Secret Key Cryptography

Hash Functions

Public Key Cryptography

MODERN CRYPTOGHRAPHY

Secret key

Secret Key(Symmetric) Cryptography uses a single key for both encryption and decryption.

SECRET KEY CRYPTOGHRAPHY

A single key is used


Sender uses the key to encrypt

Receiver uses the same key to decrypt

Key must be known to both the sender and the receiver

The difficulty is the distribution of the key

Secret key cryptography algorithms that are in use today :


Data Encryption Standard (DES):

Advanced Encryption Standard (AES):

International Data Encryption Algorithm (IDEA):

SECRET KEY SUMMARY

Hash functions(One-way cryptography) have no key since plaintext cannot be recovered from the ciphertext.

HASH FUNCTIONS

Called message compiler and one-way encryption

HASH FUNCTIONS

No key is used

Digital fingerprint

Provide the integrity

Hash algorithms that are in common use today:

HASH FUNCTIONS

Message Digest (MD) algorithms:

HAVAL (Hash of Variable Length):

Tiger:

PUBLIC KEY CRYPTOGHRAPHY

Public Key(Asymmetric) Cryptography. Two keys are used. One for encryption, one for decryption.


Developed in the last 300-400 years.

Martin Hellman and graduate student Whitfield Diffie

A two-key crypto system

Mathematical functions


Mathematical Functions :

Multiplication vs. factorization:

Exponentiation vs. logarithms:


PUBLIC KEY SUMMARY

Why Three Encryption Techniques?

Why are there so many different types of cryptographic schemes?

Why can't we do everything we need with just one ?

Every password can be decyrpted.

THE SIGNIFICANCE OF PASSWORDS

In cryptography, size does matter.

How to create & use strong Passwords

Use lengthy passwords.

Combine letters, numbers, and symbols.

How to create & use strong Passwords

Use words and phrases.

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Technology

Cryptography