Presented By:Tahir Ilyas (BSEES01121005)Iqra hamid (BSEES01121004)

Department of electronicsUniversity of Lahore

GROUP MEMBERS

‘’ The Science of Secure writing ’’

• What is cryptography ?

• Why cryptography is important ?

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

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:

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.

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.

BASIC TERMSCipher: 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”.

BASIC TERMSEncryption: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.

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 CRYPTOGRAPHYCryptography 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

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

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):

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.

PUBLIC KEY CRYPTOGHRAPHY

Developed in the last 300-400 years.

Martin Hellman and graduate student Whitfield Diffie

A two-key crypto system

Mathematical functions

PUBLIC KEY CRYPTOGHRAPHY

Mathematical Functions :

Multiplication vs. factorization:

Exponentiation vs. logarithms:

PUBLIC KEY CRYPTOGHRAPHY

PUBLIC KEY SUMMARY

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

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.

SUBSITITUTE CIPHER

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

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 100Binary 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 .

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 fiveFour and fiveKey Key Keywvfa ast wvfa

--- cipher text

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.

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.

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.

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.