Cryptographic Hash Functions

Slides:

Advertisements

Similar presentations

Hash Function. What are hash functions? Just a method of compressing strings – E.g., H : {0,1}*  {0,1} 160 – Input is called “message”, output is “digest”

Advertisements

ECE454/CS594 Computer and Network Security Dr. Jinyuan (Stella) Sun Dept. of Electrical Engineering and Computer Science University of Tennessee Fall 2011.

Digital Signatures and Hash Functions. Digital Signatures.

Session 5 Hash functions and digital signatures. Contents Hash functions – Definition – Requirements – Construction – Security – Applications 2/44.

Secure Hashing and DSS Sultan Almuhammadi ICS 454 Principles of Cryptography.

CS470, A.SelcukHash Functions1 Cryptographic Hash Functions CS 470 Introduction to Applied Cryptography Instructor: Ali Aydin Selcuk.

Hash Functions Nathanael Paul Oct. 9, Hash Functions: Introduction Cryptographic hash functions –Input – any length –Output – fixed length –H(x)

CS526Topic 5: Hash Functions and Message Authentication 1 Computer Security CS 526 Topic 5 Cryptography: Cryptographic Hash Functions And Message Authentication.

Cryptography1 CPSC 3730 Cryptography Chapter 11, 12 Message Authentication and Hash Functions.

1 Message Authentication and Hash Functions Authentication Requirements Authentication Functions Message Authentication Codes Hash Functions Security of.

Cryptography and Network Security Chapter 11 Fifth Edition by William Stallings Lecture slides by Lawrie Brown.

Lecture 15 Lecture’s outline Public algorithms (usually) that are each other’s inverse.

Acknowledgements: William Stallings.William Stallings All rights Reserved Session 4 Public Key Cryptography (Part 2) Network Security Essentials Application.

Message Authentication  message authentication is concerned with: protecting the integrity of a message protecting the integrity of a message validating.

1 Chapter 11: Message Authentication and Hash Functions Fourth Edition by William Stallings Lecture slides by Lawrie Brown (modified by Prof. M. Singhal,

Hash Functions A hash function H accepts a variable-length block of data M as input and produces a fixed-size hash value h = H(M) Principal object is.

Message Authentication Code July Message Authentication Problem  Message Authentication is concerned with:  protecting the integrity of a message.

Brand-New Hash Function   BeeM A. Satoh SCIS2006 SHA-1 Broken! Prof. Xiaoyun Wang.

CSCI 172/283 Fall 2010 Hash Functions, HMACs, and Digital Signatures.

1 Hash Functions. 2 A hash function h takes as input a message of arbitrary length and produces as output a message digest of fixed length

Cryptographic Hash Functions and Protocol Analysis

CIT 380: Securing Computer SystemsSlide #1 CIT 380: Securing Computer Systems Modern Cryptography.

MESSAGE AUTHENTICATION and HASH FUNCTIONS - Chapter 11 MESSAGE AUTHENTICATION and HASH FUNCTIONS - Chapter 11 Masquerade – message insertion, fraud, ACK.

Cryptographic Hash Functions Prepared by Dr. Lamiaa Elshenawy

Hash Functions Ramki Thurimella. 2 What is a hash function? Also known as message digest or fingerprint Compression: A function that maps arbitrarily.

Cryptographic Hash Functions

CS426Fall 2010/Lecture 51 Computer Security CS 426 Lecture 5 Cryptography: Cryptographic Hash Function.

CSCE 715: Network Systems Security Chin-Tser Huang University of South Carolina.

Hashes Lesson Introduction ●The birthday paradox and length of hash ●Secure hash function ●HMAC.

Information Security and Management 11. Cryptographic Hash Functions Chih-Hung Wang Fall

IT 221: Introduction to Information Security Principles Lecture 5: Message Authentications, Hash Functions and Hash/Mac Algorithms For Educational Purposes.

1 Message Authentication using Message Digests and the MD5 Algorithm Message authentication is important where undetected manipulation of messages can.

Data Integrity / Data Authentication. Definition Authentication (Signature) algorithm - A Verification algorithm - V Authentication key – k Verification.

@Yuan Xue 285: Network Security CS 285 Network Security Hash Algorithm Yuan Xue Fall 2012.

Hashing (Message Digest) Hello There Hashing (Message Digest)

Chapter 12 – Hash Algorithms

CS/ECE 578 Cyber Security Dr. Attila Altay Yavuz

Computer Security CS 526 Topic 4

Cryptographic Hash Functions

Cryptographic Hash Function

Secured Hash Algorithm(SHA)

A way to detect a collision…

Cryptographic Hash Functions

Presented by: Dr. Munam Ali Shah

Computer Security CS 526 Topic 4

Cryptographic Hash Functions Part I

Cryptography Lecture 13.

Cryptographic Hash Functions

ICS 454 Principles of Cryptography

Cryptography Lecture 19.

Chapter 11 – Message Authentication and Hash Functions

CS/ECE 478 Introduction to Network Security Dr. Attila Altay Yavuz

ICS 454 Principles of Cryptography

Lecture 4.1: Hash Functions: Introduction

Cryptographic Hash Functions Part I

CIS 4930/6930 – Privacy-Preserving and Trustworthy Cyber-Systems Dr

Lecture 4.1: Hash Functions, and Message Authentication Codes

Computer Security CS 526 Topic 5

Cryptography Lecture 14.

Hashing Hash are the auxiliary values that are used in cryptography.

Cryptography Lecture 13.

Cryptography Lecture 13.

Cryptography Lecture 15.

刘振上海交通大学计算机科学与工程系电信群楼3-509

Lecture 4: Hash Functions

Hash Function Requirements

CRYPTOGRAPHY & NETWORK SECURITY

Blockchains Lecture 4.

Presentation transcript:

Cryptographic Hash Functions Dr. X Slides from Dr. William Enck, NCSI

Hash Functions Hash function h: deterministic one-way function that takes as input an arbitrary message M (sometimes called a preimage) and returns as output h(M), a small fixed length hash (sometimes called a digest) Hash functions should have the following two properties: compression: reduces arbitrary length string to fixed length hash ease of computation: given message M, h(M) is easy to compute openssl speed sha

Why are hashes useful? Message authentication codes (MACs): e.g.: MACK(M) = h(K|M) (but don't do this, use HMAC instead) Modification detection codes: detect modification of data any change in data will cause change in hash

Hash functions Prof. Pedantic proposes the following hash function, arguing that it offers both compression and ease of computation. h(M) = 0 if the number of 0s in M is divisible by 3 h(M) = 1 otherwise Why is this a lousy crypto hash function?

Cryptographic Hash Functions Properties of good cryptographic hash functions: preimage resistance: given digest y, computationally infeasible to find preimage x' such that h(x')=y (also called “one-way property”) 2nd-preimage resistance: given preimage x, computationally infeasible to find preimage x' such that h(x)=h(x') (also called “weak collision resistance”) collision resistance: computationally infeasible to find preimages i,j such that h(i)=h(j) (also called “strong collision resistance”)

In other words A good cryptographic hash function has the following properties: it is deterministic so the same message always results in the same hash it is quick to compute the hash value for any given message it is infeasible to generate a message from its hash value except by trying all possible messages a small change to a message should change the hash value so extensively that the new hash value appears uncorrelated with the old hash value it is infeasible to find two different messages with the same hash value (from https://en.wikipedia.org/wiki/Cryptographic_hash_function)

Birthday Attack Birthday Paradox: chances that 2+ people share birthday in group of 23 is > 50%. General formulation function f() whose output is uniformly distributed over H possible outputs Number of experiments Q(H) until we find a collision is approximately

Practical Implications Why is this relevant to hash sizes? Choosing two messages that have the same hash h(x) = h(x’) is more practical than you might think.

Some cryptographic hash functions MD5 (128-bit digest) [don’t use this] SHA-1 (160-bit digest) [stop using this*] SHA-256 (256-bit digest) SHA-512 (512-bit digest) SHA-3 [recent competition winner]

General Structure of a Hash

Comparison of SHA parameters

SHA-512

SHA-512 function