Cryptography, a secure writing a easy presentation of networking students.

2. Presented By:
Tahir Ilyas (BSEES01121005)
Iqra hamid (BSEES01121004)
Department of electronics
University of Lahore
GROUP MEMBERS

3. ‘’ The Science of Secure writing ’’

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

5. Contents
• The purpose of cryptography
• Basic terms
• History of cryptography and cryptanalysis
• Modern cryptography(Types of Algorithms)
- Secret Key Cryptography
- Hash Functions
- Public Key Cryptography
- Methods of Cryptography
- The Significance of Passwords & Password Security
• Draw Backs of Cryptography
• Conclusion

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

7. THE PURPOSE OF CRYPTOGRAPHY
Authentication:
ensures that whoever supplies or accesses sensitive data is
an authorized party.
Privacy/confidentiality:
assures that only authorized parties are able to understand
the data.

8. THE PURPOSE OF CRYPTOGRAPHY
Integrity:
ensures that when a message is sent over a network, the
message that arrives is the same as the message that was
originally sent.
Non-repudiation:
ensuring that the intended recipient actually received the
message & ensuring that the sender actually sent the
message.

9. BASIC TERMS
Cipher:
The algorithm that does the encryption.
Ciphertext:
The encrypted version of the message. Message altered to
be unreadable by anyone except the intended recipients.
Crytanlysis:
The science of breaking cryptographic algorithms.
Cryptanalysts:
A person who breaks cryptographic codes; also referred to
as “the attacker”.

10. BASIC TERMS
Encryption:
Scrambling a message or data using a specialized
cryptographic algorithm.
Decryption:
The process of converting ciphertext back to the original
plaintext.
Key:
Sequence that controls the operation and behavior of the
cryptographic algorithm.
Plaintext:
A message in its natural format readable by an attacker.

11. 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

12. 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

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

14. MODERN CRYPTOGHRAPHY

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

16.  A single key is used
SECRET KEY CRYPTOGHRAPHY
 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

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

18. SECRET KEY SUMMARY

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

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

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

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

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

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

25. PUBLIC KEY CRYPTOGHRAPHY

26. PUBLIC KEY SUMMARY

27. METHODS OF CRYPTOGRAPHY
Cryptography
Symmetric key Asymmetric key
cryptography cryptography
(Public key cryptography)
Classical Modern
cryptography cryptography
Transposition Substitution Stream Block
cipher cipher cipher cipher

28. TRANSPOSITION CIPHER
In classical cryptography, a transposition cipher changes
one character from the plaintext to another i.e. the order of
the characters is changed.

29. SUBSITITUTE CIPHER
Substitution cipher is a method of encryption by which
units of plaintext are substituted with ciphertext according to
a regular system.

30. STREAM CIPHER
A Stream Cipher is a 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.
e.g. :
Plain text: Pay 100
Binary of plain text: 010111101 (hypothetical)
Key: 100101011 ----- Perform XOR
____________________
Cipher text 110010110 ----- ZTU9^%D
To decrypt make the XOR operation of the cipher text
with the key .

31. BLOCK CIPHER
Block cipher technique involves encryption of one block of
text at a time .Decryption also takes one block of encrypted text
at a time. Length of the block is usually 64 or 128 bits.
e.g. :
Plain text: four and five
Four and five
Key Key Key
wvfa ast wvfa --- cipher text

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

33. How to create & use strong
Passwords

34.  Use lengthy passwords.
 Combine letters, numbers, and symbols.
How to create & use strong
Passwords
 Use words and phrases.

35. Draw Backs of Cryptography
Advantages
• The biggest advantage of public key cryptography is the secure
nature of the private key. In fact it never needs to be transmitted
or revealed to anyone.
• Another type of benefit of public key cryptography is that is
provides a method for employing digital signatures.
• It enables the use of digital certificates and digital timestamps,
which is a very secure technique of authorization .We will look
at digital timestamps and digital signatures in a moment.

36. Draw Backs of Cryptography
disAdvantages
• Transmission time for documents encrypted public
key cryptography are significantly larger than
symmetric cryptography. In fact transmission of very
large documents is prohibitive.
• The key sizes must be significantly larger than
symmetric cryptography to achieve the same level of
protection.
• Public key cryptography is susceptible to
impersonation attacks.

37. CONCLUSION
Cryptography, being an art of encrypting and
decrypting confidential information and private
messages, should be implemented in the network
security to prevent any leakage and threat.
It can be done by using any of these techniques
discussed above for fortifying the personal data
transmission as well as for secure transaction.