Lecture 30. Cryptography. Symmetric Key Cryptography. Key Exchange. Advanced Encryption Standard (AES) DES. Security April 11, 2005

Size: px
Start display at page:

Download "Lecture 30. Cryptography. Symmetric Key Cryptography. Key Exchange. Advanced Encryption Standard (AES) DES. Security April 11, 2005"

Transcription

1 Lecture 30 Security April 11, 2005 Cryptography K A ciphertext Figure 7.3 goes here K B symmetric-key crypto: sender, receiver keys identical public-key crypto: encrypt key public, decrypt key secret Symmetric Key Cryptography message, m K A-B encryption algorithm ciphertext K (m) A-B K A-B decryption algorithm m = K ( K (m) ) A-B A-B symmetric key crypto: Bob and Alice share know same (symmetric) key: KA-B e.g., key is knowing substitution pattern in mono alphabetic substitution cipher Problem: how do Bob and Alice agree on key value? Key Exchange Diffie & Hellman, 1976 Exchange secret key over insecure medium Alice chooses secret value K A and Bob chooses secret value K B Alice chooses p and g, both prime numbers and g is primitive module p (can be public) Alice sends to Bob (g, p, g KA mod p) Bob send to Alice (g, p, g KB mod p) Alice computes k = (g KB mod p) KA mod p and Bob computes k = (g KA mod p) KB mod p k=k, therefore k is the new secret key DES DES: Data Encryption Standard US encryption standard [NIST 1993] 56-bit symmetric key, 64 bit input How secure is DES? DES Challenge: 56-bit-key-encrypted phrase ( Strong cryptography makes the world a safer place ) decrypted (brute force) in 4 months no known backdoor decryption approach making DES more secure use three keys sequentially (3-DES) on each datum use cipher-block chaining Advanced Encryption Standard (AES) new (Nov. 2001) symmetric-key NIST standard, replacing DES processes data in 128 bit blocks 128, 192, or 256 bit keys brute force decryption (try each key) takes 149 trillion years for AES 1

2 Public Key Cryptography symmetric key crypto requires sender, receiver know shared secret key Q: how to agree on key in first place (particularly if never met )? public key cryptography radically different approach [Diffie- Hellman76, RSA78] sender, receiver do not share secret key encryption key public (known to all) decryption key private (known only to receiver) Public Key Cryptography Figure 7.7 goes here RSA Rivest, Shamir, Adleman, 1977 Most commonly used encryption/authentication algorithm (included in Web browsers) Algorithm: use two large prime numbers to derive a public key and a private key prime numbers can be discarded keep private key secret, publish public key RSA: Choosing Keys 1. Choose two large prime numbers p, q. (e.g., 1024 bits each) 2. Compute n = pq, z = (p-1)(q-1) 3. Choose e (with e<n) that has no common factors with z. (e, z are relatively prime ). 4. Choose d such that ed-1 is exactly divisible by z. (in other words: ed mod z = 1 ). 5. Public key is (n,e). Private key is (n,d). RSA: Encryption/Decryption 0. Given (n,e) and (n,d) as computed above 1. To encrypt bit pattern, m, compute c = m e e mod n (i.e., remainder when m is divided by n) RSA Example Bob chooses p=5, q=7. Then n=35, z=24. e=5 (so e, z relatively prime). d=29 (so ed-1 exactly divisible by z). 2. To decrypt received bit pattern, c, compute m = c d mod n (i.e., remainder when c d is divided by n) encrypt: letter m m e c = m e mod n l Magic happens! m = (m e d mod n) mod n decrypt: c c d m = c d mod n letter l 2

3 Authentication Goal: Bob wants Alice to prove her identity to him Protocol ap2.0: Alice says I am Alice and sends her IP address along to prove it. Protocol ap1.0: Alice says I am Alice Protocol ap3.0: Alice says I am Alice and sends her secret password to prove it. Protocol ap3.1: Alice says I am Alice and sends her encrypted secret password to prove it. I am Alice encrypt(password) Goal: avoid playback attack Nonce: number (R) used only once in a lifetime ap4.0: to prove Alice live, Bob sends Alice nonce, R. Alice must return R, encrypted with shared secret key ap4.0 requires shared symmetric key problem: how do Bob, Alice agree on key can we authenticate using public key techniques? ap5.0: use nonce, public key cryptography Figure 7.11 goes here Figure 7.12 goes here Failures, drawbacks? 3

4 AP5.0: Security Hole? Man (woman) in the middle attack: Trudy poses as Alice (to Bob) and as Bob (to Alice) AP5.0: Security Hole? Man (woman) in the middle attack: Trudy poses as Alice (to Bob) and as Bob (to Alice) Figure 7.14 goes here Figure 7.14 goes here Need certified public keys (more later ) Need certified public keys (more later ) Digital Signatures Cryptographic technique analogous to hand-written signatures. Sender (Bob) digitally signs document, establishing he is document owner/creator. Verifiable, nonforgeable: recipient (Alice) can verify that Bob, and no one else, signed document. Simple digital signature for message m: Bob encrypts m with his private key d B, creating signed message, d B (m). Bob sends m and d B (m) to Alice. Digital Signatures Suppose Alice receives msg m, and digital signature d B (m) Alice verifies m signed by Bob by applying Bob s public key e B to d B (m) then checks e B (d B (m) ) = m. If e B (d B (m) ) = m, whoever signed m must have used Bob s private key. Alice thus verifies that: Bob signed m. No one else signed m. Bob signed m and not m. Non-repudiation: Alice can take m, and signature d B (m) to court and prove that Bob signed m. Message Digests Computationally expensive to publickey-encrypt long messages Goal: fixed-length, easyto-compute digital fingerprint apply hash function H to m, get fixed size message digest, H(m). H: Hash Function Hash function properties: many-to-1 produces fixed-size msg digest (fingerprint) given message digest x, computationally infeasible to find m such that x = H(m) Internet Checksum Internet checksum has some properties of hash function: produces fixed length digest (16-bit sum) of message is many-to-one But given message with given hash value, it is easy to find another message with same hash value: message I O U B O B ASCII format 49 4F E D2 42 B2 C1 D2 AC message I O U B O B different messages but identical checksums! ASCII format 49 4F E D2 42 B2 C1 D2 AC 4

5 Digital Signature = Signed Message Digest Bob sends digitally signed message: Alice verifies signature and integrity of digitally signed message: Hash Function Algorithms Internet checksum would make a poor message digest. Too easy to find two messages with same checksum. MD5 hash function widely used. Computes 128-bit message digest in 4-step process. arbitrary 128-bit string x, appears difficult to construct msg m whose MD5 hash is equal to x. SHA-1 is also used. US standard 160-bit message digest Trusted Intermediaries Problem: How do two entities establish shared secret key over network? Solution: trusted key distribution center (KDC) acting as intermediary between entities Problem: When Alice obtains Bob s public key (from web site, e- mail, diskette), how does she know it is Bob s public key, not Trudy s? Solution: trusted certification authority (CA) Key Distribution Center (KDC) Alice,Bob need shared symmetric key. KDC: server shares different secret key with each registered user. Alice, Bob know own symmetric keys, K A- KDC K B-KDC, for communicating with KDC. Alice communicates with KDC, gets session key R1, and K B-KDC (A,R1) Alice sends Bob K B-KDC (A,R1), Bob extracts R1 Alice, Bob now share the symmetric key R1. Certification Authorities Certification authority (CA) binds public key to particular entity. Entity (person, router, etc.) can register its public key with CA. Entity provides proof of identity to CA. CA creates certificate binding entity to public key. Certificate digitally signed by CA. When Alice wants Bob s public key: gets Bob s certificate (Bob or elsewhere). Apply CA s public key to Bob s certificate, get Bob s public key Certificate Serial number (unique to issuer) info about certificate owner, including algorithm and key value itself (not shown) info about certificate issuer valid dates digital signature by issuer 5

6 Secure Protocols Basic security algorithms are not enough: how do you use them, how do you react when something happens? Secure protocols define how basic security tools are used: provide higher levels of security by merging strengths of several basic security tools provide simple security mechanisms provide standards Examples: PGP (encryption, decryption, signature of ), SSL: secure socket layer, SSH: secure (remote) shell, HTTPS: secure HTTP Secure Alice wants to send secret message, m, to Bob. generates random symmetric private key, K S. encrypts message with K S also encrypts K S with Bob s public key. sends both K S (m) and e B (K S ) to Bob. Secure Alice wants to provide sender authentication & message integrity. Secure Alice wants to provide secrecy, sender authentication, message integrity. Alice digitally signs message. sends both message (in the clear) and digital signature. Note: Alice uses both her private key, Bob s public key. Pretty Good Privacy PGP PGP PGP designed by Phillip Zimmerman for electronic mail Uses three known techniques: IDEA for encrypting message International Data Exchange Algorithm block cipher with 64-bit blocks similar in concept but different in details from DES uses 128-bit keys patented, but free for non-commercial use RSA public key encryption permits keys up to 2,047 bits in length Digital signatures use MD5 or SHA-1 PGP generates a random 128-bit symmetric key, used by IDEA for each message PGP generates its own public/private key pairs Keys are stored locally using a hashed pass phrase PGP does not use conventional certificates (too expensive) Instead, users generate and distribute their own public keys sign each other s public keys save trusted public keys on public-key ring users build a web of trust users determine how much to trust 6

7 Pretty Good Privacy PGP Internet encryption scheme, a de-facto standard. Uses symmetric key cryptography, public key cryptography, hash function, and digital signature as described. Provides secrecy, sender authentication, integrity. Inventor, Phil Zimmerman, was target of 3-year federal investigation. A PGP signed message: ---BEGIN PGP SIGNED MESSAGE--- Hash: SHA1 Bob:My husband is out of town tonight.passionately yours, Alice ---BEGIN PGP SIGNATURE--- Version: PGP 5.0 Charset: noconv yhhjrhhgjghgg/12epj+lo8ge4vb3m qjhfevzp9t6n7g6m5gw2 ---END PGP SIGNATURE--- GPG: Gnu Privacy Guard GPG is primarily meant for securing can also use it to encrypt/decrypt/sign any message... free alternative to PGP Allows you to: create public/private key pairs encrypt/decrypt messages sign/check messages GPG Create your own public/private key pair: gpg --gen-keys you will be asked several questions: which kind of key you want, which size, how long it will stay valid, username, address, etc. (keep default values) then it will ask you for a passphrase: type any passphrase (e.g., I like rabbits very much ) your private key will be encrypted with the passphrase before storing on disk GPG will ask you for your passphrase each time it needs to access your private key Disseminating Your Public Key You can give it to anyone: people who may want to communicate with you using GPG never hand out your private key What s my public key? gpg --export --armor <Your_Name> You can add somebody else s public key to your keyring: gpg --import <filename> You can list the keys in your keyring: gpg --list-keys Encryption/Decryption with GPG Encryption: must specify the destination of your message, message will be encrypted with the recipients public key (key must be in keyring) gpg --armor --encrypt -r <recipient> < <file_to_encrypt> Decryption: GPG will use your private key to decrypt a received file, you will be asked for your passphrase gpg --decrypt < <file_to_decrypt> Signatures with GPG Sign a message (you will be asked for your passphrase): gpg --output <output_file> --clearsign <document_to_sign> message and signature will be written to output_file Check a signature: gpg --verify <document_to_check> You can encrypt and sign a document: gpg --armor --sign --encrypt -r cpoellab@cse.nd.edu < message To decrypt and check: gpg --decrypt <encrypted_and_signed_message> 7

14. Internet Security (J. Kurose)

14. Internet Security (J. Kurose) 14. Internet Security (J. Kurose) 1 Network security Foundations: what is security? cryptography authentication message integrity key distribution and certification Security in practice: application layer:

More information

Computer Networking. What is network security? Chapter 7: Network security. Symmetric key cryptography. The language of cryptography

Computer Networking. What is network security? Chapter 7: Network security. Symmetric key cryptography. The language of cryptography Chapter 7: Network security 15-441 Computer Networking Network Security: Cryptography, Authentication, Integrity Foundations: what is security? cryptography authentication message integrity key distribution

More information

Encryption. INST 346, Section 0201 April 3, 2018

Encryption. INST 346, Section 0201 April 3, 2018 Encryption INST 346, Section 0201 April 3, 2018 Goals for Today Symmetric Key Encryption Public Key Encryption Certificate Authorities Secure Sockets Layer Simple encryption scheme substitution cipher:

More information

Internet and Intranet Protocols and Applications

Internet and Intranet Protocols and Applications Internet and Intranet Protocols and Applications Lecture 10: Internet and Network Security April 9, 2003 Arthur Goldberg Computer Science Department New York University artg@cs.nyu.edu What is network

More information

CS Computer Networks 1: Authentication

CS Computer Networks 1: Authentication CS 3251- Computer Networks 1: Authentication Professor Patrick Traynor 4/14/11 Lecture 25 Announcements Homework 3 is due next class. Submit via T-Square or in person. Project 3 has been graded. Scores

More information

Kurose & Ross, Chapters (5 th ed.)

Kurose & Ross, Chapters (5 th ed.) Kurose & Ross, Chapters 8.2-8.3 (5 th ed.) Slides adapted from: J. Kurose & K. Ross \ Computer Networking: A Top Down Approach (5 th ed.) Addison-Wesley, April 2009. Copyright 1996-2010, J.F Kurose and

More information

Network Security. Computer Networking: A Top Down Approach Featuring the Internet, 2 nd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2002.

Network Security. Computer Networking: A Top Down Approach Featuring the Internet, 2 nd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2002. Network Security Computer Networking: A Top Down Approach Featuring the Internet, 1. What is network security 2. Principles of cryptography 3. Authentication 4. Integrity 5. Key Distribution and certification

More information

Chapter 8 Security. Computer Networking: A Top Down Approach. 6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012

Chapter 8 Security. Computer Networking: A Top Down Approach. 6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 Chapter 8 Security A note on the use of these ppt slides: We re making these slides freely available to all (faculty, students, readers). They re in PowerPoint form so you see the animations; and can add,

More information

SECURITY IN NETWORKS 1

SECURITY IN NETWORKS 1 SECURITY IN NETWORKS 1 GOALS Understand principles of network security: Cryptography and its many uses beyond con dentiality Authentication Message integrity 2. 1 WHAT IS NETWORK SECURITY? Con dentiality:

More information

ח'/סיון/תשע "א. RSA: getting ready. Public Key Cryptography. Public key cryptography. Public key encryption algorithms

ח'/סיון/תשע א. RSA: getting ready. Public Key Cryptography. Public key cryptography. Public key encryption algorithms Public Key Cryptography Kurose & Ross, Chapters 8.28.3 (5 th ed.) Slides adapted from: J. Kurose & K. Ross \ Computer Networking: A Top Down Approach (5 th ed.) AddisonWesley, April 2009. Copyright 19962010,

More information

SECURITY IN NETWORKS

SECURITY IN NETWORKS SECURITY IN NETWORKS GOALS Understand principles of network security: Cryptography and its many uses beyond con dentiality Authentication Message integrity WHAT IS NETWORK SECURITY? Con dentiality: only

More information

CSC 8560 Computer Networks: Network Security

CSC 8560 Computer Networks: Network Security CSC 8560 Computer Networks: Network Security Professor Henry Carter Fall 2017 Last Time We talked about mobility as a matter of context: How is mobility handled as you move around a room? Between rooms

More information

The Network Security Model. What can an adversary do? Who might Bob and Alice be? Computer Networks 12/2/2009. CSC 257/457 - Fall

The Network Security Model. What can an adversary do? Who might Bob and Alice be? Computer Networks 12/2/2009. CSC 257/457 - Fall The Network Security Model Bob and lice want to communicate securely. Trudy (the adversary) has access to the channel. Kai Shen lice data channel secure sender data, control s secure receiver Bob data

More information

Ref:

Ref: Cryptography & digital signature Dec. 2013 Ref: http://cis.poly.edu/~ross/ 2 Cryptography Overview Symmetric Key Cryptography Public Key Cryptography Message integrity and digital signatures References:

More information

Chapter 8. Computer Networking: A Top Down Approach Featuring the Internet, 3 rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004.

Chapter 8. Computer Networking: A Top Down Approach Featuring the Internet, 3 rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004. Chapter 8 Network Security A note on the use of these ppt slides: We re making these slides freely available to all (faculty, students, readers). They re in PowerPoint form so you can add, modify, and

More information

Computer Networks 1 (Mạng Máy Tính 1) Lectured by: Dr. Phạm Trần Vũ

Computer Networks 1 (Mạng Máy Tính 1) Lectured by: Dr. Phạm Trần Vũ Computer Networks 1 (Mạng Máy Tính 1) Lectured by: Dr. Phạm Trần Vũ Chapter 8 Network Security Computer Networking: A Top Down Approach, 5 th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009.

More information

CS 332 Computer Networks Security

CS 332 Computer Networks Security CS 332 Computer Networks Security Professor Szajda Last Time We talked about mobility as a matter of context: How is mobility handled as you move around a room? Between rooms in the same building? As your

More information

Computer Communication Networks Network Security

Computer Communication Networks Network Security Computer Communication Networks Network Security ICEN/ICSI 416 Fall 2016 Prof. Dola Saha 1 Network Security Goals: understand principles of network security: cryptography and its many uses beyond confidentiality

More information

Security: Focus of Control. Authentication

Security: Focus of Control. Authentication Security: Focus of Control Three approaches for protection against security threats a) Protection against invalid operations b) Protection against unauthorized invocations c) Protection against unauthorized

More information

UNIT - IV Cryptographic Hash Function 31.1

UNIT - IV Cryptographic Hash Function 31.1 UNIT - IV Cryptographic Hash Function 31.1 31-11 SECURITY SERVICES Network security can provide five services. Four of these services are related to the message exchanged using the network. The fifth service

More information

CSC/ECE 774 Advanced Network Security

CSC/ECE 774 Advanced Network Security Computer Science CSC/ECE 774 Advanced Network Security Topic 2. Network Security Primitives CSC/ECE 774 Dr. Peng Ning 1 Outline Absolute basics Encryption/Decryption; Digital signatures; D-H key exchange;

More information

Chapter 8 Network Security

Chapter 8 Network Security Chapter 8 Network Security A note on the use of these ppt slides: We re making these slides freely available to all (faculty, students, readers). They re in PowerPoint form so you can add, modify, and

More information

Security: Focus of Control

Security: Focus of Control Security: Focus of Control Three approaches for protection against security threats a) Protection against invalid operations b) Protection against unauthorized invocations c) Protection against unauthorized

More information

Lecture 9a: Secure Sockets Layer (SSL) March, 2004

Lecture 9a: Secure Sockets Layer (SSL) March, 2004 Internet and Intranet Protocols and Applications Lecture 9a: Secure Sockets Layer (SSL) March, 2004 Arthur Goldberg Computer Science Department New York University artg@cs.nyu.edu Security Achieved by

More information

Lecture 2 Applied Cryptography (Part 2)

Lecture 2 Applied Cryptography (Part 2) Lecture 2 Applied Cryptography (Part 2) Patrick P. C. Lee Tsinghua Summer Course 2010 2-1 Roadmap Number theory Public key cryptography RSA Diffie-Hellman DSA Certificates Tsinghua Summer Course 2010 2-2

More information

CSC 774 Network Security

CSC 774 Network Security CSC 774 Network Security Topic 2. Review of Cryptographic Techniques CSC 774 Dr. Peng Ning 1 Outline Encryption/Decryption Digital signatures Hash functions Pseudo random functions Key exchange/agreement/distribution

More information

Public Key Cryptography, OpenPGP, and Enigmail. 31/5/ Geek Girls Carrffots GVA

Public Key Cryptography, OpenPGP, and Enigmail. 31/5/ Geek Girls Carrffots GVA Public Key Cryptography, OpenPGP, and Enigmail Cryptography is the art and science of transforming (encrypting) a message so only the intended recipient can read it Symmetric Cryptography shared secret

More information

Computer Networks. Wenzhong Li. Nanjing University

Computer Networks. Wenzhong Li. Nanjing University Computer Networks Wenzhong Li Nanjing University 1 Chapter 7. Network Security Network Attacks Cryptographic Technologies Message Integrity and Authentication Key Distribution Firewalls Transport Layer

More information

CSCI 454/554 Computer and Network Security. Topic 5.2 Public Key Cryptography

CSCI 454/554 Computer and Network Security. Topic 5.2 Public Key Cryptography CSCI 454/554 Computer and Network Security Topic 5.2 Public Key Cryptography Outline 1. Introduction 2. RSA 3. Diffie-Hellman Key Exchange 4. Digital Signature Standard 2 Introduction Public Key Cryptography

More information

Outline. CSCI 454/554 Computer and Network Security. Introduction. Topic 5.2 Public Key Cryptography. 1. Introduction 2. RSA

Outline. CSCI 454/554 Computer and Network Security. Introduction. Topic 5.2 Public Key Cryptography. 1. Introduction 2. RSA CSCI 454/554 Computer and Network Security Topic 5.2 Public Key Cryptography 1. Introduction 2. RSA Outline 3. Diffie-Hellman Key Exchange 4. Digital Signature Standard 2 Introduction Public Key Cryptography

More information

Chapter 9 Public Key Cryptography. WANG YANG

Chapter 9 Public Key Cryptography. WANG YANG Chapter 9 Public Key Cryptography WANG YANG wyang@njnet.edu.cn Content Introduction RSA Diffie-Hellman Key Exchange Introduction Public Key Cryptography plaintext encryption ciphertext decryption plaintext

More information

Distributed Systems. 26. Cryptographic Systems: An Introduction. Paul Krzyzanowski. Rutgers University. Fall 2015

Distributed Systems. 26. Cryptographic Systems: An Introduction. Paul Krzyzanowski. Rutgers University. Fall 2015 Distributed Systems 26. Cryptographic Systems: An Introduction Paul Krzyzanowski Rutgers University Fall 2015 1 Cryptography Security Cryptography may be a component of a secure system Adding cryptography

More information

9/30/2016. Cryptography Basics. Outline. Encryption/Decryption. Cryptanalysis. Caesar Cipher. Mono-Alphabetic Ciphers

9/30/2016. Cryptography Basics. Outline. Encryption/Decryption. Cryptanalysis. Caesar Cipher. Mono-Alphabetic Ciphers Cryptography Basics IT443 Network Security Administration Slides courtesy of Bo Sheng Basic concepts in cryptography systems Secret cryptography Public cryptography 1 2 Encryption/Decryption Cryptanalysis

More information

Outline. Public Key Cryptography. Applications of Public Key Crypto. Applications (Cont d)

Outline. Public Key Cryptography. Applications of Public Key Crypto. Applications (Cont d) Outline AIT 682: Network and Systems Security 1. Introduction 2. RSA 3. Diffie-Hellman Key Exchange 4. Digital Signature Standard Topic 5.2 Public Key Cryptography Instructor: Dr. Kun Sun 2 Public Key

More information

Cryptography Basics. IT443 Network Security Administration Slides courtesy of Bo Sheng

Cryptography Basics. IT443 Network Security Administration Slides courtesy of Bo Sheng Cryptography Basics IT443 Network Security Administration Slides courtesy of Bo Sheng 1 Outline Basic concepts in cryptography systems Secret key cryptography Public key cryptography Hash functions 2 Encryption/Decryption

More information

Application Security and Wireless Applications

Application Security and Wireless Applications Application Security and Wireless Applications Silvia Giordano DTI - SUPSI University of Applied Science, Manno Switzerland silvia.giordano@supsi.ch SUPSI-DTI Silvia Giordano 10/06/2004 Security, Network

More information

Cryptography (Overview)

Cryptography (Overview) Cryptography (Overview) Some history Caesar cipher, rot13 substitution ciphers, etc. Enigma (Turing) Modern secret key cryptography DES, AES Public key cryptography RSA, digital signatures Cryptography

More information

Security+ Guide to Network Security Fundamentals, Third Edition. Chapter 11 Basic Cryptography

Security+ Guide to Network Security Fundamentals, Third Edition. Chapter 11 Basic Cryptography Security+ Guide to Network Security Fundamentals, Third Edition Chapter 11 Basic Cryptography Objectives Define cryptography Describe hashing List the basic symmetric cryptographic algorithms 2 Objectives

More information

Information Security. message M. fingerprint f = H(M) one-way hash. 4/19/2006 Information Security 1

Information Security. message M. fingerprint f = H(M) one-way hash. 4/19/2006 Information Security 1 Information Security message M one-way hash fingerprint f = H(M) 4/19/2006 Information Security 1 Outline and Reading Digital signatures Definition RSA signature and verification One-way hash functions

More information

CSE 3461/5461: Introduction to Computer Networking and Internet Technologies. Network Security. Presentation L

CSE 3461/5461: Introduction to Computer Networking and Internet Technologies. Network Security. Presentation L CS 3461/5461: Introduction to Computer Networking and Internet Technologies Network Security Study: 21.1 21.5 Kannan Srinivasan 11-27-2012 Security Attacks, Services and Mechanisms Security Attack: Any

More information

Cristina Nita-Rotaru. CS355: Cryptography. Lecture 17: X509. PGP. Authentication protocols. Key establishment.

Cristina Nita-Rotaru. CS355: Cryptography. Lecture 17: X509. PGP. Authentication protocols. Key establishment. CS355: Cryptography Lecture 17: X509. PGP. Authentication protocols. Key establishment. Public Keys and Trust Public Key:P A Secret key: S A Public Key:P B Secret key: S B How are public keys stored How

More information

Public Key Algorithms

Public Key Algorithms Public Key Algorithms 1 Public Key Algorithms It is necessary to know some number theory to really understand how and why public key algorithms work Most of the public key algorithms are based on modular

More information

Welcome to CS 395/495 Internet Security: A Measurement-based Approach

Welcome to CS 395/495 Internet Security: A Measurement-based Approach Welcome to CS 395/495 Internet Security: A Measurement-based Approach Why Internet Security Internet attacks are increasing in frequency, severity and sophistication Denial of service (DoS) attacks Cost

More information

1.264 Lecture 28. Cryptography: Asymmetric keys

1.264 Lecture 28. Cryptography: Asymmetric keys 1.264 Lecture 28 Cryptography: Asymmetric keys Next class: Anderson chapters 20. Exercise due before class (Reading doesn t cover same topics as lecture) 1 Asymmetric or public key encryption Receiver

More information

CSC 474/574 Information Systems Security

CSC 474/574 Information Systems Security CSC 474/574 Information Systems Security Topic 2.1 Introduction to Cryptography CSC 474/574 By Dr. Peng Ning 1 Cryptography Cryptography Original meaning: The art of secret writing Becoming a science that

More information

Public Key Algorithms

Public Key Algorithms Public Key Algorithms CS 472 Spring 13 Lecture 6 Mohammad Almalag 2/19/2013 Public Key Algorithms - Introduction Public key algorithms are a motley crew, how? All hash algorithms do the same thing: Take

More information

APNIC elearning: Cryptography Basics

APNIC elearning: Cryptography Basics APNIC elearning: Cryptography Basics 27 MAY 2015 03:00 PM AEST Brisbane (UTC+10) Issue Date: Revision: Introduction Presenter Sheryl Hermoso Training Officer sheryl@apnic.net Specialties: Network Security

More information

Applied Networks & Security

Applied Networks & Security Applied Networks & Security Crypto with Critical Analysis http://condor.depaul.edu/~jkristof/it263/ John Kristoff jtk@depaul.edu IT 263 Winter 2006/2007 John Kristoff - DePaul University 1 Critical analysis

More information

CSE 127: Computer Security Cryptography. Kirill Levchenko

CSE 127: Computer Security Cryptography. Kirill Levchenko CSE 127: Computer Security Cryptography Kirill Levchenko October 24, 2017 Motivation Two parties want to communicate securely Secrecy: No one else can read messages Integrity: messages cannot be modified

More information

Modern cryptography 2. CSCI 470: Web Science Keith Vertanen

Modern cryptography 2. CSCI 470: Web Science Keith Vertanen Modern cryptography 2 CSCI 470: Web Science Keith Vertanen Modern cryptography Overview Asymmetric cryptography Diffie-Hellman key exchange (last time) Pubic key: RSA Pretty Good Privacy (PGP) Digital

More information

ISA 662 Internet Security Protocols. Outline. Prime Numbers (I) Beauty of Mathematics. Division (II) Division (I)

ISA 662 Internet Security Protocols. Outline. Prime Numbers (I) Beauty of Mathematics. Division (II) Division (I) Outline ISA 662 Internet Security Protocols Some Math Essentials & History Asymmetric signatures and key exchange Asymmetric encryption Symmetric MACs Lecture 2 ISA 662 1 2 Beauty of Mathematics Demonstration

More information

Introduction to Cryptography. Vasil Slavov William Jewell College

Introduction to Cryptography. Vasil Slavov William Jewell College Introduction to Cryptography Vasil Slavov William Jewell College Crypto definitions Cryptography studies how to keep messages secure Cryptanalysis studies how to break ciphertext Cryptology branch of mathematics,

More information

Cryptography & Key Exchange Protocols. Faculty of Computer Science & Engineering HCMC University of Technology

Cryptography & Key Exchange Protocols. Faculty of Computer Science & Engineering HCMC University of Technology Cryptography & Key Exchange Protocols Faculty of Computer Science & Engineering HCMC University of Technology Outline 1 Cryptography-related concepts 2 3 4 5 6 7 Key channel for symmetric cryptosystems

More information

David Wetherall, with some slides from Radia Perlman s security lectures.

David Wetherall, with some slides from Radia Perlman s security lectures. David Wetherall, with some slides from Radia Perlman s security lectures. djw@cs.washington.edu Networks are shared: Want to secure communication between legitimate participants from others with (passive

More information

Chapter 9. Public Key Cryptography, RSA And Key Management

Chapter 9. Public Key Cryptography, RSA And Key Management Chapter 9 Public Key Cryptography, RSA And Key Management RSA by Rivest, Shamir & Adleman of MIT in 1977 The most widely used public-key cryptosystem is RSA. The difficulty of attacking RSA is based on

More information

Basic Concepts and Definitions. CSC/ECE 574 Computer and Network Security. Outline

Basic Concepts and Definitions. CSC/ECE 574 Computer and Network Security. Outline CSC/ECE 574 Computer and Network Security Topic 2. Introduction to Cryptography 1 Outline Basic Crypto Concepts and Definitions Some Early (Breakable) Cryptosystems Key Issues 2 Basic Concepts and Definitions

More information

06/02/ Local & Metropolitan Area Networks. 0. Overview. Terminology ACOE322. Lecture 8 Network Security

06/02/ Local & Metropolitan Area Networks. 0. Overview. Terminology ACOE322. Lecture 8 Network Security 1 Local & Metropolitan Area Networks ACOE322 Lecture 8 Network Security Dr. L. Christofi 1 0. Overview As the knowledge of computer networking and protocols has become more widespread, so the threat of

More information

Cryptography and Network Security. Sixth Edition by William Stallings

Cryptography and Network Security. Sixth Edition by William Stallings Cryptography and Network Security Sixth Edition by William Stallings Chapter 9 Public Key Cryptography and RSA Misconceptions Concerning Public-Key Encryption Public-key encryption is more secure from

More information

CRYPTOGRAPHY & DIGITAL SIGNATURE

CRYPTOGRAPHY & DIGITAL SIGNATURE UNIT V CRYPTOGRAPHY & DIGITAL SIGNATURE What happens in real life? We have universal electronic connectivity via networks of our computers so allowing viruses and hackers to do eavesdropping. So both the

More information

Encryption Algorithms Authentication Protocols Message Integrity Protocols Key Distribution Firewalls

Encryption Algorithms Authentication Protocols Message Integrity Protocols Key Distribution Firewalls Security Outline Encryption Algorithms Authentication Protocols Message Integrity Protocols Key Distribution Firewalls Overview Cryptography functions Secret key (e.g., DES) Public key (e.g., RSA) Message

More information

Public Key Cryptography

Public Key Cryptography graphy CSS322: Security and Cryptography Sirindhorn International Institute of Technology Thammasat University Prepared by Steven Gordon on 29 December 2011 CSS322Y11S2L07, Steve/Courses/2011/S2/CSS322/Lectures/rsa.tex,

More information

Diffie-Hellman. Part 1 Cryptography 136

Diffie-Hellman. Part 1 Cryptography 136 Diffie-Hellman Part 1 Cryptography 136 Diffie-Hellman Invented by Williamson (GCHQ) and, independently, by D and H (Stanford) A key exchange algorithm o Used to establish a shared symmetric key Not for

More information

Using Cryptography CMSC 414. October 16, 2017

Using Cryptography CMSC 414. October 16, 2017 Using Cryptography CMSC 414 October 16, 2017 Digital Certificates Recall: K pub = (n, e) This is an RSA public key How do we know who this is for? Need to bind identity to a public key We can do this using

More information

Network Security. Chapter 8. MYcsvtu Notes.

Network Security. Chapter 8. MYcsvtu Notes. Network Security Chapter 8 Network Security Some people who cause security problems and why. Cryptography Introduction Substitution ciphers Transposition ciphers One-time pads Fundamental cryptographic

More information

Issues. Separation of. Distributed system security. Security services. Security policies. Security mechanism

Issues. Separation of. Distributed system security. Security services. Security policies. Security mechanism Module 9 - Security Issues Separation of Security policies Precise definition of which entities in the system can take what actions Security mechanism Means of enforcing that policy Distributed system

More information

Public Key Algorithms

Public Key Algorithms CSE597B: Special Topics in Network and Systems Security Public Key Cryptography Instructor: Sencun Zhu The Pennsylvania State University Public Key Algorithms Public key algorithms RSA: encryption and

More information

Computer Security: Principles and Practice

Computer Security: Principles and Practice Computer Security: Principles and Practice Chapter 2 Cryptographic Tools First Edition by William Stallings and Lawrie Brown Lecture slides by Lawrie Brown Cryptographic Tools cryptographic algorithms

More information

Security. Communication security. System Security

Security. Communication security. System Security Security Communication security security of data channel typical assumption: adversary has access to the physical link over which data is transmitted cryptographic separation is necessary System Security

More information

CSC 474/574 Information Systems Security

CSC 474/574 Information Systems Security CSC 474/574 Information Systems Security Topic 2.5 Public Key Algorithms CSC 474/574 Dr. Peng Ning 1 Public Key Algorithms Public key algorithms covered in this class RSA: encryption and digital signature

More information

User Authentication. Modified By: Dr. Ramzi Saifan

User Authentication. Modified By: Dr. Ramzi Saifan User Authentication Modified By: Dr. Ramzi Saifan Authentication Verifying the identity of another entity Computer authenticating to another computer Person authenticating to a local/remote computer Important

More information

Cryptography (DES+RSA) by Amit Konar Dept. of Math and CS, UMSL

Cryptography (DES+RSA) by Amit Konar Dept. of Math and CS, UMSL Cryptography (DES+RSA) by Amit Konar Dept. of Math and CS, UMSL Transpositional Ciphers-A Review Decryption 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 Encryption 1 2 3 4 5 6 7 8 A G O O D F R I E N D I S A T R E

More information

L13. Reviews. Rocky K. C. Chang, April 10, 2015

L13. Reviews. Rocky K. C. Chang, April 10, 2015 L13. Reviews Rocky K. C. Chang, April 10, 2015 1 Foci of this course Understand the 3 fundamental cryptographic functions and how they are used in network security. Understand the main elements in securing

More information

Lecture Nov. 21 st 2006 Dan Wendlandt ISP D ISP B ISP C ISP A. Bob. Alice. Denial-of-Service. Password Cracking. Traffic.

Lecture Nov. 21 st 2006 Dan Wendlandt ISP D ISP B ISP C ISP A. Bob. Alice. Denial-of-Service. Password Cracking. Traffic. 15-441 Lecture Nov. 21 st 2006 Dan Wendlandt Worms & Viruses Phishing End-host impersonation Denial-of-Service Route Hijacks Traffic modification Spyware Trojan Horse Password Cracking IP Spoofing DNS

More information

The evolving storage encryption market

The evolving storage encryption market The evolving storage encryption market Alexander (S andy) S tewart S un M icros ys tems 1 S toragetek Drive, Louis ville, CO 80028 P hone:+1-303-673-2775 FAX: +1-303-661-5743 E-mail: alexander.s tewart@

More information

Public Key Cryptography

Public Key Cryptography Public Key Cryptography Giuseppe F. Italiano Universita` di Roma Tor Vergata italiano@disp.uniroma2.it Motivation Until early 70s, cryptography was mostly owned by government and military Symmetric cryptography

More information

User Authentication. Modified By: Dr. Ramzi Saifan

User Authentication. Modified By: Dr. Ramzi Saifan User Authentication Modified By: Dr. Ramzi Saifan Authentication Verifying the identity of another entity Computer authenticating to another computer Person authenticating to a local/remote computer Important

More information

CSCI 454/554 Computer and Network Security. Topic 2. Introduction to Cryptography

CSCI 454/554 Computer and Network Security. Topic 2. Introduction to Cryptography CSCI 454/554 Computer and Network Security Topic 2. Introduction to Cryptography Outline Basic Crypto Concepts and Definitions Some Early (Breakable) Cryptosystems Key Issues 2 Basic Concepts and Definitions

More information

Module: Cryptographic Protocols. Professor Patrick McDaniel Spring CMPSC443 - Introduction to Computer and Network Security

Module: Cryptographic Protocols. Professor Patrick McDaniel Spring CMPSC443 - Introduction to Computer and Network Security CMPSC443 - Introduction to Computer and Network Security Module: Cryptographic Protocols Professor Patrick McDaniel Spring 2009 1 Key Distribution/Agreement Key Distribution is the process where we assign

More information

Network Security Chapter 8

Network Security Chapter 8 Network Security Chapter 8 Cryptography Symmetric-Key Algorithms Public-Key Algorithms Digital Signatures Management of Public Keys Communication Security Authentication Protocols Email Security Web Security

More information

Key Exchange. References: Applied Cryptography, Bruce Schneier Cryptography and Network Securiy, Willian Stallings

Key Exchange. References: Applied Cryptography, Bruce Schneier Cryptography and Network Securiy, Willian Stallings Key Exchange References: Applied Cryptography, Bruce Schneier Cryptography and Network Securiy, Willian Stallings Outlines Primitives Root Discrete Logarithm Diffie-Hellman ElGamal Shamir s Three Pass

More information

CT30A8800 Secured communications

CT30A8800 Secured communications CT30A8800 Secured communications Pekka Jäppinen October 31, 2007 Pekka Jäppinen, Lappeenranta University of Technology: October 31, 2007 Secured Communications: Key exchange Schneier, Applied Cryptography:

More information

Outline. Cryptography. Encryption/Decryption. Basic Concepts and Definitions. Cryptography vs. Steganography. Cryptography: the art of secret writing

Outline. Cryptography. Encryption/Decryption. Basic Concepts and Definitions. Cryptography vs. Steganography. Cryptography: the art of secret writing Outline CSCI 454/554 Computer and Network Security Basic Crypto Concepts and Definitions Some Early (Breakable) Cryptosystems Key Issues Topic 2. Introduction to Cryptography 2 Cryptography Basic Concepts

More information

Other Topics in Cryptography. Truong Tuan Anh

Other Topics in Cryptography. Truong Tuan Anh Other Topics in Cryptography Truong Tuan Anh 2 Outline Public-key cryptosystem Cryptographic hash functions Signature schemes Public-Key Cryptography Truong Tuan Anh CSE-HCMUT 4 Outline Public-key cryptosystem

More information

(2½ hours) Total Marks: 75

(2½ hours) Total Marks: 75 (2½ hours) Total Marks: 75 N. B.: (1) All questions are compulsory. (2) Makesuitable assumptions wherever necessary and state the assumptions made. (3) Answers to the same question must be written together.

More information

Cryptography. some history. modern secret key cryptography. public key cryptography. cryptography in practice

Cryptography. some history. modern secret key cryptography. public key cryptography. cryptography in practice Cryptography some history Caesar cipher, rot13 substitution ciphers, etc. Enigma (Turing) modern secret key cryptography DES, AES public key cryptography RSA, digital signatures cryptography in practice

More information

1.264 Lecture 27. Security protocols Symmetric cryptography. Next class: Anderson chapter 10. Exercise due after class

1.264 Lecture 27. Security protocols Symmetric cryptography. Next class: Anderson chapter 10. Exercise due after class 1.264 Lecture 27 Security protocols Symmetric cryptography Next class: Anderson chapter 10. Exercise due after class 1 Exercise: hotel keys What is the protocol? What attacks are possible? Copy Cut and

More information

Overview. SSL Cryptography Overview CHAPTER 1

Overview. SSL Cryptography Overview CHAPTER 1 CHAPTER 1 Secure Sockets Layer (SSL) is an application-level protocol that provides encryption technology for the Internet. SSL ensures the secure transmission of data between a client and a server through

More information

Elements of Cryptography and Computer and Networking Security Computer Science 134 (COMPSCI 134) Fall 2016 Instructor: Karim ElDefrawy

Elements of Cryptography and Computer and Networking Security Computer Science 134 (COMPSCI 134) Fall 2016 Instructor: Karim ElDefrawy Elements of Cryptography and Computer and Networking Security Computer Science 134 (COMPSCI 134) Fall 2016 Instructor: Karim ElDefrawy Homework 2 Due: Friday, 10/28/2016 at 11:55pm PT Will be posted on

More information

Security: Cryptography

Security: Cryptography Security: Cryptography Computer Science and Engineering College of Engineering The Ohio State University Lecture 38 Some High-Level Goals Confidentiality Non-authorized users have limited access Integrity

More information

Public-key Cryptography: Theory and Practice

Public-key Cryptography: Theory and Practice Public-key Cryptography Theory and Practice Department of Computer Science and Engineering Indian Institute of Technology Kharagpur Chapter 1: Overview What is Cryptography? Cryptography is the study of

More information

Introduction and Overview. Why CSCI 454/554?

Introduction and Overview. Why CSCI 454/554? Introduction and Overview CSCI 454/554 Why CSCI 454/554? Get Credits and Graduate Security is important More job opportunities More research funds 1 Workload Five homework assignments Two exams (open book

More information

Dr. Jinyuan (Stella) Sun Dept. of Electrical Engineering and Computer Science University of Tennessee Fall 2010

Dr. Jinyuan (Stella) Sun Dept. of Electrical Engineering and Computer Science University of Tennessee Fall 2010 CS 494/594 Computer and Network Security Dr. Jinyuan (Stella) Sun Dept. of Electrical Engineering and Computer Science University of Tennessee Fall 2010 1 Public Key Cryptography Modular Arithmetic RSA

More information

Cryptography. Cryptography is everywhere. German Lorenz cipher machine

Cryptography. Cryptography is everywhere. German Lorenz cipher machine Crypto 101 Cryptography Cryptography is everywhere German Lorenz cipher machine 2 Cryptography Cryptography deals with creating documents that can be shared secretly over public communication channels

More information

Topics. Number Theory Review. Public Key Cryptography

Topics. Number Theory Review. Public Key Cryptography Public Key Cryptography Topics 1. Number Theory Review 2. Public Key Cryptography 3. One-Way Trapdoor Functions 4. Diffie-Helman Key Exchange 5. RSA Cipher 6. Modern Steganography Number Theory Review

More information

CS 6324: Information Security More Info on Key Establishment: RSA, DH & QKD

CS 6324: Information Security More Info on Key Establishment: RSA, DH & QKD ERIK JONSSON SCHOOL OF ENGINEERING & COMPUTER SCIENCE Cyber Security Research and Education Institute CS 6324: Information Security Dr. Junia Valente Department of Computer Science The University of Texas

More information

Lecture 4: Cryptography III; Security. Course Administration

Lecture 4: Cryptography III;  Security. Course Administration Lecture 4: Cryptography III; Email Security CS 336/536: Computer Network Security Fall 2014 Nitesh Saxena Course Administration HW/Lab 1 Posted Due at 11am on Sep 29 Labs are active starting this week

More information

Data Communication Prof.A.Pal Dept of Computer Science & Engineering Indian Institute of Technology, Kharagpur Lecture - 40 Secured Communication - II

Data Communication Prof.A.Pal Dept of Computer Science & Engineering Indian Institute of Technology, Kharagpur Lecture - 40 Secured Communication - II Data Communication Prof.A.Pal Dept of Computer Science & Engineering Indian Institute of Technology, Kharagpur Lecture - 40 Secured Communication - II Hello and welcome to today's lecture on secured communication.

More information

Lecture 6 - Cryptography

Lecture 6 - Cryptography Lecture 6 - Cryptography CMPSC 443 - Spring 2012 Introduction Computer and Network Security Professor Jaeger www.cse.psu.edu/~tjaeger/cse443-s12 Question Setup: Assume you and I donʼt know anything about

More information

Gestion et sécurité des réseaux informatiques. Guy Leduc. Chapter 3: Securing applications. Chapter goals: security in practice:

Gestion et sécurité des réseaux informatiques. Guy Leduc. Chapter 3: Securing applications. Chapter goals: security in practice: Gestion et sécurité des réseaux informatiques Guy Leduc Chapter 3: Securing applications Computer Networking: A Top Down Approach, 4 th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007. (section

More information

key distribution requirements for public key algorithms asymmetric (or public) key algorithms

key distribution requirements for public key algorithms asymmetric (or public) key algorithms topics: cis3.2 electronic commerce 24 april 2006 lecture # 22 internet security (part 2) finish from last time: symmetric (single key) and asymmetric (public key) methods different cryptographic systems

More information