an overview of cryptography ying wang-suorsa helsinki university of technology

An Overview of Cryptography

Ying Wang-SuorsaHelsinki University of Technology

Objectives

To provide you with an introduction to cryptology Some terms and concepts behind basic

cryptographic methods Some basic cryptographic algorithms Trust models

Cryptography : the art of providing securecommunication over insecure channels.Encode text and provide a method for decodingNot hide message!

Confidentiality : Ensuring that no one can readthe message except intended receiver.Authentication : The process of proving one'sidentity.Integrity : Ensuring the received messages has notbeen altered in any way from the original.Non-repudiation : A mechanism to prove that thesender really sent this message.

Levels of CryptographicAction – In today's internet, most Syst. are split between application level and transport level.

7 – Application

6 – Presentation

5 – Session S-HTTP

4 – Transport SSL

3 – Network IPSEC

2 – Data Link PPTP

1 – Physical

Importance of Cryptography

Military applications : command and controlDiplomatic applications : information gathering, spyEconomic applications : Information protectionBanking transactionAuthentication and signaturesModern e-commerce

How can the public use cryptography quickly and safely?

Importance of Cryptography

Modern methods of communication are inherentlyinsecure

Internet is very insecure Ethernet networks liable to having sniffers Cable modems pass through other people's homes

Pre-computerized Crypto schemes

Transposition Ciphers Reverse pairs of lettersHELLO WORLDEHLL OOWLRD Remover every second letter and put it at the endHELLO WORLDHLOWRDEL OL Reverse the lettersHELLO WORLDDLROW OLLEH Many trickers...

Pre-computerized Crypto schemes

Substitution Ciphers

ABCDEFGHIJKLMNOPQRSTUVWXYZBADCFEHGJILKNMPORQTSVUXWZY

HELLO WORLD GFKKPXPQKC

Types of Cryptographic Algorithms

Why Three Encryption Techniques?

The answer lies in that each scheme is optimized for some specific applications

Trust Models

PGP Web of Trust

Kerberos

Public Key Certificates and CertificateAuthorities

Kerberos Architecture