This document discusses the science of encryption through three main topics: the purpose and history of cryptography, modern cryptography techniques, and password security. It describes cryptography as the science of secure communications and its goals of authentication, privacy, integrity, and non-repudiation. The history of cryptography is divided into ancient uses and electro-mechanical machines of World War II. Modern techniques discussed are secret key cryptography, hash functions, and public key cryptography. It emphasizes the importance of strong, unique passwords for security.

1. ‘’ The Science of encrypTion ’’

2. • What is cryptography ?
• Why cryptography is important ?

3. 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

4. THE PURPOSE OF CRYPTOGRAPHY
Specific security requirements for communication:
Data transfer and telecommunication
Science of communications code
Computer writing in secret
 Authentication:
 Privacy/confidentiality:
 Integrity:
 Non-repudiation:

5. HISTORY OF CRYPTOGRAPHY
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.

6. HISTORY OF CRYPTOGRAPHY
Cryptography was used in three kinds of contexts in
Cryptography::
ancient times
 Private communications
Greek κρυπτός, kryptos,
 Art and religion
"hidden, secret"
 Military and diplomatic use

7. MODERN CRYPTOGHRAPHY
Here we have three types of algorithms that we can
talk about:
 Secret Key Cryptography
 Hash Functions
 Public Key Cryptography

8. MODERN CRYPTOGHRAPHY

9. SECRET KEY CRYPTOGHRAPHY
 Secret Key(Symmetric) Cryptography uses a single
key for both encryption and decryption.

10. 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

11. SECRET KEY CRYPTOGHRAPHY
Secret key cryptography algorithms that are in use
today :
 Data Encryption Standard (DES):
 Advanced Encryption Standard (AES):
 International Data Encryption Algorithm (IDEA):

12. SECRET KEY SUMMARY

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

14. HASH FUNCTIONS
 Called message compiler and one-way encryption
 No key is used
 Digital fingerprint
 Provide the integrity

15. HASH FUNCTIONS
Hash algorithms that are in common use today:
 Message Digest (MD) algorithms:
 HAVAL (Hash of Variable Length):
 Tiger:

16. PUBLIC KEY CRYPTOGHRAPHY
 Public Key(Asymmetric) Cryptography. Two keys are
used. One for encryption, one for decryption.

17. PUBLIC KEY CRYPTOGHRAPHY
 Developed in the last 300-400 years.
 Martin Hellman and graduate student Whitfield
Diffie
 A two-key crypto system
 Mathematical functions

18. PUBLIC KEY CRYPTOGHRAPHY
Mathematical Functions :
 Multiplication vs. factorization:
 Exponentiation vs. logarithms:

19. PUBLIC KEY CRYPTOGHRAPHY

20. PUBLIC KEY SUMMARY

21. 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 ?

22. THE SIGNIFICANCE OF PASSWORDS
 Every password can be decyrpted.
 In cryptography, size does matter.

23. How to create & use strong
Passwords

24. How to create & use strong
Passwords
 Use lengthy passwords.
THANK YOU symbols.
 Combine letters, numbers, and
FOR LISTENING TO US (:
 Use words and phrases.