Introduction to Cryptography (1)

Slides:



Advertisements
Similar presentations
Sri Lanka Institute of Information Technology
Advertisements

Computer Science CSC 474By Dr. Peng Ning1 CSC 474 Information Systems Security Topic 2.1 Introduction to Cryptography.
CS 6262 Spring 02 - Lecture #7 (Tuesday, 1/29/2002) Introduction to Cryptography.
1 Introduction CSE 5351: Introduction to cryptography Reading assignment: Chapter 1 of Katz & Lindell.
BY MUKTADIUR RAHMAN MAY 06, 2010 INTERODUCTION TO CRYPTOGRAPHY.
Cryptographic Technologies
Security Internet Management & Security 06 Learning outcomes At the end of this session, you should be able to: –Describe the reasons for having system.
CS1001 Lecture 24. Overview Encryption Encryption Artificial Intelligence Artificial Intelligence Homework 4 Homework 4.
Dr Alejandra Flores-Mosri Security Internet Management & Security 06 Learning outcomes At the end of this session, you should be able to: –Describe the.
CRYPTOGRAPHIC DATA INTEGRITY ALGORITHMS
Encryption is a way to transform a message so that only the sender and recipient can read, see or understand it. The mechanism is based on the use of.
CS5204 – Fall Cryptographic Security Presenter: Hamid Al-Hamadi October 13, 2009.
1 Cryptography Basics. 2 Cryptography Basic terminologies Symmetric key encryption Asymmetric key encryption Public Key Infrastructure Digital Certificates.
Message Authentication  message authentication is concerned with: protecting the integrity of a message protecting the integrity of a message validating.
Cryptography, Authentication and Digital Signatures
CS526: Information Security Prof. Sam Wagstaff September 16, 2003 Cryptography Basics.
Fall 2002CS 395: Computer Security1 Chapter 11: Message Authentication and Hash Functions.
Advanced Database Course (ESED5204) Eng. Hanan Alyazji University of Palestine Software Engineering Department.
Lecture 2: Introduction to Cryptography
Intro to Cryptography Lesson Introduction
IT 221: Introduction to Information Security Principles Lecture 5: Message Authentications, Hash Functions and Hash/Mac Algorithms For Educational Purposes.
Cryptographic Security Aveek Chakraborty CS5204 – Operating Systems1.
Security. Security Needs Computers and data are used by the authorized persons Computers and their accessories, data, and information are available to.
Cryptographic Hash Function. A hash function H accepts a variable-length block of data as input and produces a fixed-size hash value h = H(M). The principal.
CS/ECE 578 Cyber-Security Dr. Attila Altay Yavuz
Basics of Cryptography
CS/ECE Network Security Dr. Attila Altay Yavuz
ISA 400 Management of Information Security
Symmetric Cryptography
IT443 – Network Security Administration Instructor: Bo Sheng
USAGE OF CRYPTOGRAPHY IN NETWORK SECURITY
ISA 330 Introduction to Proactive System Security
Cryptographic Hash Functions
Cryptographic Hash Function
Message Authentication and Hash Functions
Outline Desirable characteristics of ciphers Uses of cryptography
Cryptography and Security Technologies
Encryption
Basic Network Encryption
Cryptography.
Cryptographic Hash Functions
Presented by: Dr. Munam Ali Shah
NET 311 Information Security
Cryptographic Hash Functions Part I
Cryptography Basics and Symmetric Cryptography
Mumtaz Ali Rajput +92 – INFORMATION SECURITY – WEEK 2 Mumtaz Ali Rajput +92 – 301-
مروري برالگوريتمهاي رمز متقارن(كليد پنهان)
Security through Encryption
Message Authentication and Hash Functions
Chapter 11 – Message Authentication and Hash Functions
CS/ECE 478 Network Security Dr. Attila Altay Yavuz
Security.
Message Authentication and Hash Functions
CDK4: Chapter 7 CDK5: Chapter 11 TvS: Chapter 9
NETW4005 COMPUTER SECURITY - A
Cryptography Reference: Network Security
Network Security - A Lecture 1 - NETW4006 NETW4006-Lecture01 1.
CDK: Chapter 7 TvS: Chapter 9
Chapter -7 CRYPTOGRAPHIC HASH FUNCTIONS
DISSERTATION ON CRYPTOGRAPHY.
Basic Network Encryption
Security: Integrity, Authentication, Non-repudiation
CRYPTOGRAPHY & NETWORK SECURITY
Chapter 8 roadmap 8.1 What is network security?
Presentation transcript:

Introduction to Cryptography (1)

What is Cryptography Cryptography Cryptanalysis Cryptology In a narrow sense Mangling information into apparent unintelligibility Allowing a secret method of un-mangling In a broader sense Mathematical techniques related to information security About secure communication in the presence of adversaries Cryptanalysis The study of methods for obtaining the meaning of encrypted information without accessing the secret information Cryptology Cryptography + cryptanalysis

Security Attacks Passive attacks Active attacks Obtain message contents Monitoring traffic flows Active attacks Masquerade of one entity as some other Replay previous messages Modify messages in transmit Add, delete messages Denial of service

Objectives of Information Security Confidentiality (secrecy) Only the sender and intended receiver should be able to understand the contents of the transmitted message Authentication Both the sender and receiver need to confirm the identity of other party involved in the communication Data integrity The content of their communication is not altered, either maliciously or by accident, in transmission. Availability Timely accessibility of data to authorized entities.

Objectives of Information Security Non-repudiation An entity is prevented from denying its previous commitments or actions Access control An entity cannot access any entity that it is not authorized to. Anonymity The identity of an entity if protected from others.

Types of Cryptographic Functions Secret key functions Public key functions Hash functions

Secret Key Cryptography encryption plaintext ciphertext key ciphertext plaintext decryption Using a single key for encryption/decryption. The plaintext and the ciphertext having the same size. Also called symmetric key cryptography

SKC: Security Uses Transmitting over an insecure channel The transmitted message is encrypted by the sender and can be decrypted by the receiver, with the same key Prevent attackers from eavesdropping Secure storage on insecure media Data is encrypted before being stored somewhere Only the entities knowing the key can decrypt it

SKC: Security Uses Authentication Strong authentication: proving knowledge of a secret without revealing it. Alice Bob challenge r A response rA encrypted with KA,B r B rB encrypted with KA,B

SKC: Security Uses Integrity Check Noncryptographic checksum Using a well-known algorithm to map a message (of arbitrary length) to a fixed-length checksum Protecting against accidental corruption of a message Example: CRC Cryptographic checksum A well-know algorithm Given a key and a message The algorithm produces a fixed-length message authentication code (MAC) that is sent with the message

Public Key Cryptography encryption plaintext ciphertext Public key Private key ciphertext plaintext decryption Each individual has two keys a private key (d): need not be reveal to anyone a public key (e): preferably known to the entire world Public key crypto is also called asymmetric crypto.

PKC: Security Uses Transmitting over an insecure channel Alice Bob encrypt mA using dB encrypt mA using eB Secure storage on insecure media Data is encrypted with the public key of the source, before being stored somewhere Nobody else can decrypt it (not knowing the private key of the data source)

PKC: Security Uses Authentication Alice Bob encrypt r using eB decrypt to r using dB r

PKC: Security Uses Digital Signatures signing plaintext Signed message Proving that a message is generated by a particular individual Non-repudiation: the signing individual can not be denied, because only him/her knows the private key. signing plaintext Signed message Private key Public key Signed message plaintext verification

Hash Functions Cryptographic hash function Properties A mathematical transformation that takes a message of arbitrary length and computes it a fixed-length (short) number. Properties ( Let the hash of a message m be h(m) ) For any m, it is relatively easy to compute h(m) Given h(m), there is no way to find an m that hashes to h(m) in a way that is substantially easier than going through all possible values of m and computing h(m) for each one. It is computationally infeasible to find two values that hash to the same thing.

Hash Functions: Security Uses Password hashing The system store a hash of the password (not the password itself) When a password is supplied, it computes the password’s hash and compares it with the stored value. Message integrity Using cryptographic hash functions to generate a MAC Bob Alice secret =? message hash hash secret

Hash Functions: Security Uses Message fingerprint Save the message digest of the data on a tamper-proof backing store Periodically re-compute the digest of the data to ensure it is not changed. Downline load security Using a hash function to ensure a download program is not modified Improving signature efficiency Compute a message digest (using a hash function) and sign that.

Cryptographic Algorithms: Agenda Attacks on cryptographic algorithms Definition of security Some cryptographic algorithms: basic facts

Attacks: Types Brute force search Cryptoanalysis Assume either know/recognize plaintext Simply try every key Cryptoanalysis Ciphertext only With the ciphertext Plaintext is recognizable Known plaintext <cipher, plaintext> pairs are known Chosen plaintext Select plaintext and obtain ciphertext to attack

Birthday Attacks Principle Attack: message replay Assume: A function yields any of n different outputs with equal probability, where n is sufficiently large. After evaluating the function for about 1.2*squart(n) arguments, we expect to find a pair of different arguments, x1 and x2, such that f(x1)=f(x2). Attack: message replay Solution: increase the size of the output

Meet-in-the-Middle Attacks Principle build a table of keys Compute f(k,m) for every key f is an encryption function, m is a known message Eavesdrop a value f(k’,m) If f(k’,m)=f(k,m), then there is a good chance k’=k.

Meet-in-the-Middle Attacks An attack example Assume: a new encryption function: F(k1,k2,m)=f(k1,f(k2,m)) A pair (P,C) is known Attacker: Encrypt P, i.e., computing f(k2,P), for all possible values of k2; store the values in a table Decrypt C, i.e., computing f-1(k1,C), for all possible values of k1, and for each result check the table A match reveals a possible combination of the keys

Security Definition Unconditional Security Computational security The system cannot be defeated, no matter how much power is available by the adversary. Computational security The perceived level of computation required to defeat the system using the best known attack exceeds, by a comfortable margin, the computational resources of the hypothesized adversary. e.g., given limited computing resources, it takes the age of universe to break cipher.

Security Definition Provable security Ad hoc security The difficulty of defeating the system can be shown to be essentially as difficult as solving a well-known and supposedly difficult problem (e.g., integer factorization) Ad hoc security Claims of security generally remain questionable Unforeseen attacks remain a threat

Secret Key Cryptographic Algorithms DES (Data Encryption Standard) 3DES (Triple DES) IDEA (International Data Encryption Algorithm) AES (Advanced Encryption Standard)

DES (Data Encryption Standard) Authors: NSA & IBM, 1977 Data block size: 64-bit (64-bit input, 64-bit output) Key size: 56-bit key Encryption is fast DES chips DES software: a 500-MIP CPU can encrypt at about 30K octets per second Security No longer considered secure: 56 bit keys are vulnerable to exhaustive search

Triple-DES (3DES) C = DESk3(DESk2(DESk1(P))). Data block size: 64-bit Key size: 168-bit key; effective key size: 112 (due to man-in-the-middle attack) Encryption is slower than DES Securer than DES

IDEA (International Data Encryption Algorithm) Authors: Lai & Massey, 1991 Data block size: 64-bit Key size: 128-bit Encryption is slower than DES Security Nobody has yet published results on how to break it Having patent protection

AES (Advanced Encryption Standard) Authors: Daemen & Rijmen Block size:128-bit Key size: 128-bit, 192-bit, 256-bit Encryption is fast Security As of 2005, no successful attacks are recognized. NSA stated it secure enough for non-classified data.