Cryptography & Security

Slides:



Advertisements
Similar presentations
Cryptography in World War II Jefferson Institute for Lifelong Learning at UVa Spring 2006 David Evans Class 4: Modern Cryptography
Advertisements

BY MUKTADIUR RAHMAN MAY 06, 2010 INTERODUCTION TO CRYPTOGRAPHY.
8-1 What is network security? Confidentiality: only sender, intended receiver should “understand” message contents m sender encrypts message m receiver.
Symmetric Key Distribution Protocol with Hybrid Crypto Systems Tony Nguyen.
Network Security – Part 2 V.T. Raja, Ph.D., Oregon State University.
Network Security – Part 2 (Continued) Lecture Notes for May 8, 2006 V.T. Raja, Ph.D., Oregon State University.
CS110: Computers and the Internet Encryption and Certificates.
Encryption: A Brief History Author: Margery Waldron.
1 Cryptography NOTES. 2 Secret Key Cryptography Single key used to encrypt and decrypt. Key must be known by both parties. Assuming we live in a hostile.
Encryption Questions answered in this lecture: How does encryption provide privacy? How does encryption provide authentication? What is public key encryption?
Chapter 3 (B) – Key Management; Other Public Key Cryptosystems.
Upper OSI Layers Natawut Nupairoj, Ph.D. Department of Computer Engineering Chulalongkorn University.
Lecture 2: Introduction to Cryptography
Overview of Cryptography & Its Applications
Encryption. Introduction The incredible growth of the Internet has excited businesses and consumers alike with its promise of changing the way we live.
Encryption CS110: Computer Science and the Internet.
Lecture 9 Overview. Digital Signature Properties CS 450/650 Lecture 9: Digital Signatures 2 Unforgeable: Only the signer can produce his/her signature.
Department of Computer Science Chapter 5 Introduction to Cryptography Semester 1.
SSL: Secure Socket Layer By: Mike Weissert. Overview Definition History & Background SSL Assurances SSL Session Problems Attacks & Defenses.
Secret Key Cryptography
Encryption with Keys and Passwords
Key management issues in PGP
Web Applications Security Cryptography 1
Basics of Cryptography
Security Outline Encryption Algorithms Authentication Protocols
Digital Signatures Cryptographic technique analogous to hand-written signatures. sender (Bob) digitally signs document, establishing he is document owner/creator.
Cryptography Why Cryptography Symmetric Encryption
Computer Communication & Networks
Privacy & Security.
Cryptography Reference: Network Security
Cryptography Reference: Network Security
Encryption. Encryption Basics • Plaintext - the original message ABCDEFG • Ciphertext - the coded message DFDFSDFSD • Cipher - algorithm for.
What is network security?
Security.
12. Encryption on the Internet
Basic Network Encryption
Chapter 30 Cryptography Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Introduction to security goals and usage of cryptographic algorithms
Cryptography.
CSCI-235 Micro-Computer Applications
Cryptography Basics and Symmetric Cryptography
Chapter 7 STRENGTH OF ENCRYPTION & Public Key Infrastructure
Encryption NSA – used to be able to crack most codes, technology has changed that Encryption is the art of encoding messages so they can’t be understood.
Network Security Basics
Security through Encryption
Introduction to Symmetric-key and Public-key Cryptography
Encryption NSA – used to be able to crack most codes, technology has changed that. Now other methods are applied by NSA to access transmissions (see 2013.
Security.
CDK4: Chapter 7 CDK5: Chapter 11 TvS: Chapter 9
Protocol ap1.0: Alice says “I am Alice”
MSIT 543 Cryptography Concepts and Techniques Symmetric Key Encryption
Chapter 4 Cryptography / Encryption
Cryptography Reference: Network Security
Discrete Math for CS CMPSC 360 LECTURE 14 Last time:
Lecture 10: Network Security.
CDK: Chapter 7 TvS: Chapter 9
Encryption NSA – used to be able to crack most codes, technology has changed that Encryption is the art of encoding messages so they can’t be understood.
Slide design: Dr. Mark L. Hornick
Chapter 29 Cryptography and Network Security
Basic Network Encryption
Digital Signatures Cryptographic technique analogous to hand-written signatures. sender (Bob) digitally signs document, establishing he is document owner/creator.
Public – Private Key Cryptography
Basic of Modern Cryptography
Modern Cryptography.
Security: Integrity, Authentication, Non-repudiation
Chapter 8 roadmap 8.1 What is network security?
Secure Diffie-Hellman Algorithm
Introduction to Cryptography
Presentation transcript:

Cryptography & Security CSC 103 Lecture 12 Nicholas R. Howe

What does this message say? Frqjudwxodwlrqv, brx kdyh iljxuhg rxw krz wr wudqvodwh wkh vhfuhw phvvdjh. Zhoo grqh! How did you figure it out? What techniques did you use? Can you figure out the one below? Oelp kz ymssfql cbwpvt kvllkxi. Zqp xpomjufc nqfgvk jlsszt bz grr ehivank ry kenn o vgxjhjnr ndr.

Encryption Schemes The first shifts every letter by 3: Congratulations, you have figured out how to… + 333333333333333, 333 3333 3333333 333 333 33… Frqjudwxodwlrqv, brx kdyh iljxuhg rxw krz wr… The second uses a one-time pad: This is another secret message. + Vxdx ch yzezymu kxuyra yrttkre. Oelp kz ymssfql cbwpvt kvllkxi. One-time pad is unbreakable if used just once. This would be ideal cipher The problem is distributing it!

Generated Cipher E-commerce: Delivery of keys is a problem Idea: generate pseudorandom ciphers using short keys Cipher sequence impossible to guess without key Still a problem of key delivery Example: Key = 4-digit number Square it & take middle 4 digits Repeat using new key, etc. 4472 x 4472 19998784 9987 x 9987 99740169

Codebreaking in WWII Germans in WWII used mechanical cipher generators Allies able to deduce mechanism and decipher messages Significant factor in war effort Early application of computers at Bletchley Park, U.K. Interesting books on topic Lorenz cipher Enigma cipher

Code Breaking Scenario: Alice wants to speak with Bob Eve is listening to their communications Can Alice and Bob converse without Eve learning anything? Alice Bob Eve

Public Key Cryptography Key distribution remains problem 1970s: Public key schemes published Rely on one-way function Example: multiplying two numbers is easy Factoring a number into two components is hard Setup: two keys, one public, one private Encryption via one key is undone using the other Impossible* to decrypt otherwise 1531 x 1811 = ? 2772641 = ? x ? M =M

Key Exchange Alice and Bob independently select public & private keys Eve

Key Exchange Alice and Bob independently select public & private keys Alice & Bob exchange public keys B A B A A B Alice Bob B A Eve B A

Secure Communication (?) Alice sends messages to Bob encrypted using Bob’s public key Only Bob has the private key that can decrypt the message M A B B A B Alice Bob ? B A Eve B

Man In The Middle Attack What if Eve is able to alter messages sent between Alice and Bob? Eve can intercept key exchange & substitute new key! A B A E A B Alice Bob A E Eve E E A

Man In The Middle Attack What if Eve is able to alter messages sent between Alice and Bob? Eve can intercept key exchange & substitute new key! All subsequent messages read & altered A M B M E E A B Alice Bob E A E A Eve E E A B

Secure Key Distribution To prevent man-in-the-middle, must ensure correct identity of public keys Need a trusted source to hold keys Source must verify identity of entities for which it holds keys Verification in person, not electronically Keys also handed over in person Web: trusted source is Certificate Authority

Certificates Public/private keys can also establish identity Browsers have CA public keys built in CA can send unforgeable messages Can distribute public keys for other sites Secure, verifiable communication M This message can only be generated using the CA private key. It can be decoded using the CA public key. CA CA M Message readable only by B, sendable only by A B A

How Secure? Best encryption systems based upon one-way functions with no known solution Alternative is brute force: try every possible key Time to break based upon key length Key size Time to Crack 40-bits (pre-1996) Seconds 56 bits (DES) Days 64 bits (RC5) Years 128-256 bits (AES) Secure (currently)

Crypto Algorithms Many developments in 1990’s: U.S. law prohibited export of crypto greater than 40 bits as “munitions” Government using Data Encryption Standard (DES) 54 bit key considered weak Fear of NSA “backdoor” NIST announces competition for Advanced Encryption Standard (AES) in 1997, adopted 2000

Personal Crypto You can make a personal encryption key OpenPGP (Pretty Good Privacy) offers free encryption standards & tools Exchange public keys with friend Can encrypt email before sending Can also create a key with public CA Must verify your identity to CA Send and receive encrypted messages in GMail

Key Exchange Alice and Bob independently select public & private keys Bob’s public key available from trusted source Alice sends her public key to Bob encoded using Bob’s public key Alice Bob Eve A B A B

Key Exchange Alice and Bob independently select public & private keys Bob’s public key available from trusted source B A B A B Alice Bob B Eve B