CRYPTOGRAPHY

TOPICS OF SEMINAR

• Introduction & Related Terms• Categories and Aspects of

cryptography• Model of Network Security• Encryption Techniques• Public key cryptosystem• Application• Bibliography

DEFINATION OF CRYPTOGRAPHY• Cryptography is the study of

mathematical techniques related to the aspects of information security, such as confidentially, data integrity and entity authentication.

• Cryptography is not only means of providing information, but rather one set of techniques.

Related Terms

• Plain text :-Original Message• Cipher text:-Coded Message.• Encryption:-The process of converting

plain text into cipher

text.• Decryption:-Restoring plain text from cipher text.

• Cryptography:-The science or area of Encryption & Decryption • Cryptanalysis:-The science of analysis or breaking of secure communication • Cryptology :- The area of cryptography and cryptanalysis together

Categories OF CRYPTOGRAPHY

There are two types of cryptographic algorithm

• Symmetric key

• Asymmetric key

GOALS OF CRYPTOGRAPHY

• Confidentially• Data Integrity• Authentication• Non-repudiation

ASPECTS OF SECURITY

• Security Service

• Security Mechanism

• Security Attacks Passive Attacks Active Attacks

MODEL OF NETWORK SECURITY

There are four basic tasks in designing a particular security services.

• Design an algorithm• Generate a secret information • Develop methods for distribution

and sharing• Specify the protocol

SUBSTITUTION TECHNIQUES• CAESAR CIPHER• To Encrypt using Caesar's key value of

3,we offset the alphabet so that the 3rd letter down (D) begins the alphabet.

• ABCDEFGHIJKLMNOPQRSTUVWXYZ and sliding everything up by 3, you get DEFGHIJKLMNOPQRSTUVWXYZABC where D=A, E=B, F=C, and so on.

• "SECRET" encrypts as "VHFUHW."

TRANSPOSITION TECHNIQUES• Plain text = “meet me after this

party”• Key = 2• m e m a t r h s a t e t e f e t i p r y• Cipher text

=“mematrshsatetefetipry”

A more complex scheme is • Key 4 3 1 2 5 6 7• plaintext: a t t a c k p o s t p o n e d u n t I l t• Ciphertext:

TTNAPTTSUAODCOLKNLPET

DES ALGORITHM

Public Key Cryptosystem: Secrecy

Encryption Algorithm

Source A

Source Destination

Decryption Algorithm

Key pair source

Cryptanalyst

Destination B

B’s public key

B’s private key

Public Key Cryptosystem: Authentication

Encryption Algorithm

Source A

Source Destination

Decryption Algorithm

Key pair source

Cryptanalyst

Destination B

A’s private key

A’s public key

Public Key Cryptosystem: Secrecy & Authentication

Encry.Algori-them

Encry.Algori-them

Decry.Algori-them

Decry.Algori-them

Source

Dest.

Key Pair Source

Key Pair Source

B’s private key B’s public key

A’s public key

Source A

Destination B

A’s private key

APPLICATION

• Secure Communication

• Identification & Authentication

• Secret Sharing

BIBLIOGRAPHY

• Cryptography & Network Security By William Stallings

• WWW.google.com• Computer Network By Andrew S.

Tanenbaum

THANK YOU