cis5372 1 intro
DESCRIPTION
fdkmkdfTRANSCRIPT
![Page 1: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/1.jpg)
CIS-5372: 24.August.2015 1
Bogdan Carbunar
Presented by Mozhgan Azimpourkivi
CIS-5372
Foundations of Computer Security
Class 1
![Page 2: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/2.jpg)
CIS-5372: 24.August.2015 2
Administrative Issues
Rules of the Class
Textbooks
Information Assurance Overview
Outline
![Page 3: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/3.jpg)
CIS-5372: 24.August.2015 3
Staff Bogdan Carbunar, assistant prof.
Communications Class web page: http://users.cis.fiu.edu/~carbunar/teaching/cis5372/cis5372.2015/cis5372.html E-mail: [email protected]
Office Hours After class, ECS 383
What about you ?
Administrative Issues
![Page 4: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/4.jpg)
CIS-5372: 24.August.2015 4
1 midterm worth: 25%
Final worth: 35%
Homework worth: 20%
Class participation: 20%
15% Extra credit!:
5%: User study participation
10%: student paper presentations
Class Grading (subject to changes)
![Page 5: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/5.jpg)
CIS-5372: 24.August.2015 5
Homework
3 homeworks
Around 2 weeks for each homework
Not intended for grade (that much), but for your training
Midterm and Final
Problems similar to the homeworks
Class Grading: Details
![Page 6: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/6.jpg)
CIS-5372: 24.August.2015 6
Class participation: 20%
Class presence does not mean participation
But it is encouraged
Participation means asking and answering questions
Class Grading: Details (cont’d)
![Page 7: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/7.jpg)
CIS-5372: 24.August.2015 7
Student paper presentations: 10%
Papers posted on class web page
Let me know in time (FIFO assignment rule)
User study participation: 5%
Not yet sure
Will provide more details later
Class Grading: Details (cont’d)
![Page 8: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/8.jpg)
CIS-5372: 24.August.2015 8
Use Bell curving: see https://en.wikipedia.org/wiki/Grading_on_a_curve
Based on mean and standard deviation of numeric scores
Class Grading: Final Grade
This is an example
![Page 9: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/9.jpg)
CIS-5372: 24.August.2015 9
Administrative Issues
Rules of the Class
Textbooks
Information Assurance Overview
Outline
![Page 10: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/10.jpg)
CIS-5372: 24.August.2015 10
Rule #1: 0 tolerance for cheating First occurrence: grade 0 (zero) for problems
involved Second occurrence: …
Rule #2: The midterm and final exam are given only once,
at the time and place specified (at the proper time) on the web page
If you miss the exam, you get grade 0 Exception: medical condition, if properly
documented
Rules of Class
![Page 11: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/11.jpg)
CIS-5372: 24.August.2015 11
Administrative Issues
Rules of the Class
Textbooks
Information Assurance Overview
Outline
![Page 12: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/12.jpg)
CIS-5372: 24.August.2015 12
Security In Computing – 4th edition
Pfleeger and Pfleeger
Cryptography and Network Security
William Stallings
Applied Cryptography – 2nd edition
Bruce Schneier; Available online; Don’t need to buy it!
http://www.wikipedia.org/
Papers assigned for reading
See class webpage
Textbooks
![Page 13: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/13.jpg)
CIS-5372: 24.August.2015 13
Administrative Issues
Rules of the Class
Textbooks
Information Assurance Overview
Outline
![Page 14: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/14.jpg)
CIS-5372: 24.August.2015 14
Administrative Issues
Rules of the Class
Textbooks
Information Assurance Overview
Outline
![Page 15: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/15.jpg)
CIS-5372: 24.August.2015 15
Branch of computer technology known as information security as applied to computers and networks
Objective: protection of information and property Theft, corruption, or natural disaster, while allowing the
information and property to remain accessible and productive to its intended users
[Source: wikipedia]
Computer Security
![Page 16: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/16.jpg)
CIS-5372: 24.August.2015 16
Security: protect information and information systems from unauthorized access, use, disclosure, disruption, modification, inspection, recording or destruction.
Privacy: relationship between collection and dissemination of data, technology, the public expectation of privacy, and the legal and political issues surrounding them
[Source: wikipedia]
Information Security & Privacy
![Page 17: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/17.jpg)
CIS-5372: 24.August.2015 17
It’s a jungle out there
3 Examples: Blue Security
Slammer Worm
Titan Rain
Many, many more …
Why Do We Care ?
![Page 18: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/18.jpg)
CIS-5372: 24.August.2015 18
Anti-spam company “Blue Security”
Active approach against spam – Blue Frog Distributed Denial of service attack against spammers May 2006: attacked by PharmaMaster
Distributed denial of service attack (DDOS) Heavy network traffic (requests) against Blue Security Blue Security redirects traffic to its weblog, hosted by Six
Apart
Blue Security DoS
![Page 19: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/19.jpg)
CIS-5372: 24.August.2015 19
Six Apart server farm collapses Makes 2,000 other blogs unreachable for several hours
Blue Security folds
Its clients were affected (down)
Find more details online (wiki?)
Blue Security DoS
![Page 20: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/20.jpg)
CIS-5372: 24.August.2015 20
January 2003 Infects 90% of vulnerable computers within 10 minutes
Effect of the Worm Interference with elections
Cancelled airline flights
911 emergency systems affected in Seattle
13,000 Bank of America ATMs failed
No malicious payload!
Estimated ~$1 Billion in productivity loss
Slammer Worm
![Page 21: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/21.jpg)
CIS-5372: 24.August.2015 21
Successful net intrusions on U.S. military Increasing in frequency since 2003
Originating from China, etc
Successful intrusion into… U.S. Army Information Systems Engineering Command at
Fort Huachuca, Arizona
Defense Information Systems Agency in Arlington, Virginia
Naval Ocean Systems Center in San Diego, California
United States Army Space and Strategic Defense installation in Huntsville, Alabama
more…
Titan Rain
![Page 22: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/22.jpg)
CIS-5372: 24.August.2015 22
Goals: Protect
Confidentiality
Integrity
Availability
Integrity
Confidentiality
Availability
Information Security
Information Security
![Page 23: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/23.jpg)
CIS-5372: 24.August.2015 23
Information about system or its users cannot be learned by an attacker
Data Confidentiality:
Private or confidential information is not revealed to unauthorized individuals
Privacy:
Users control what information about them can be Collected
Stored
By whom
Confidentiality
Confidentiality
![Page 24: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/24.jpg)
CIS-5372: 24.August.2015 24
The system continues to operate properly, only reaching states that would occur if there were no attacker
Data Integrity
Information and programs are changed only in specified and authorized manner
System Integrity
System performs intended function free from unauthorized system manipulation
Integrity
Integrity
![Page 25: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/25.jpg)
CIS-5372: 24.August.2015 25
Actions by an attacker do not prevent users from having access to use of the system
Enable access to data and resources
Timely response
Fair resource allocation
Availability
Availability
![Page 26: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/26.jpg)
CIS-5372: 24.August.2015 26
Authenticity
Being able to be verified and trusted
Confidence in the validity of a message (originator)
Accountability
Actions of an entity can be traced to it
Tracing a security breach to a responsible party
More Required Concepts
![Page 27: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/27.jpg)
CIS-5372: 24.August.2015 27
System
Security is about
Honest user (e.g., Alice, Bob, …)
Dishonest Attacker
How the Attacker Disrupts honest user’s use of the system (Integrity, Availability)
Learns information intended for Alice only (Confidentiality)
Alice Malory
General Picture
![Page 28: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/28.jpg)
CIS-5372: 24.August.2015 28
Examples
Confidentiality
Student grades
Available only to student, parents, employer
Integrity
Patient information e.g., allergies
Can lead to loss of human life
Availability
Authentication service
Unavailability can lead to financial loss
![Page 29: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/29.jpg)
CIS-5372: 24.August.2015 29
Passive Attacks
Learn and use information from a system without affecting system resources
Active Attacks
Attempt to affect and alter system resources
Security Attacks
![Page 30: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/30.jpg)
CIS-5372: 24.August.2015 30
Passive Attacks
Alice
Bob Eavesdrop 2
Eve
M 1
Perform traffic analysis
on encrypted messages
3
![Page 31: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/31.jpg)
CIS-5372: 24.August.2015 31
Impersonation
Replay
Modify messages
Denial of Service (DoS)
Active Attacks
![Page 32: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/32.jpg)
CIS-5372: 24.August.2015 32
Impersonation
Alice
Bob Eavesdrop 2
Malory
Hi, A 1
Hi, “I’m A” 3
May enable M to obtain
A’s privileges
![Page 33: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/33.jpg)
CIS-5372: 24.August.2015 33
Replay
Alice
Bob Eavesdrop 2
Malory
“You owe me $10” 1
You owe me $10 3
Bob owes Alice $20 or Bob owes Malory $10
![Page 34: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/34.jpg)
CIS-5372: 24.August.2015 34
Message Modification
Alice
Bob Eavesdrop 2
Malory
Give Carol access 1
Give Malory acc 3
Note that A’s message is delayed or removed
![Page 35: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/35.jpg)
CIS-5372: 24.August.2015 35
Denial of Service
Alice
Bob
Malory
Hi, I’m Alice 1
A can never talk to B
Send Key 2
![Page 36: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/36.jpg)
CIS-5372: 24.August.2015 36
Building blocks that we will define and use in the next lectures
Will describe in more detail later
Encryption
Signature
Hash
Crash Course in Crypto
![Page 37: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/37.jpg)
CIS-5372: 24.August.2015 37
Basic Terminology
Plaintext
Original message
Ciphertext
Coded message
Cipher or Encryption Algorithm
Algorithm for transforming plaintext to ciphertext
Key
Info used in cipher known only to sender/receiver
![Page 38: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/38.jpg)
CIS-5372: 24.August.2015 38
Basic Terminology (cont’d)
Encrypt (encipher)
Converting plaintext to ciphertext
Decrypt (decipher)
Recovering plaintext from ciphertext
![Page 39: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/39.jpg)
CIS-5372: 24.August.2015 39
Basic Terminology (cont’d)
Cryptography
Study of encryption principles/methods
Cryptanalysis (codebreaking)
Study of principles/ methods of deciphering ciphertext
without knowing key
Cryptology
Field of both cryptography and cryptanalysis
![Page 40: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/40.jpg)
CIS-5372: 24.August.2015 40
Cryptosystem/Encryption System
Plaintext
Encryption
Algorithm
Encryption Key Decryption Key
Plaintext
Decryption
Algorithm
Ciphertext
![Page 41: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/41.jpg)
CIS-5372: 24.August.2015 41
Symmetric Cryptosystems
Plaintext
Encryption
Algorithm
Encryption Key Decryption Key
Plaintext
Decryption
Algorithm =
Ciphertext
![Page 42: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/42.jpg)
CIS-5372: 24.August.2015 42
1. Strong encryption algorithm
2. Secret key known only to sender / receiver
Mathematically:
Ciphertext = E(K, Plaintext) = EK(Plaintext)
Plaintext = D(K, Ciphertext) = DK(Ciphertext)
3. Assume encryption algorithm is known !
4. Assume a secure channel to distribute key
Requirements
![Page 43: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/43.jpg)
CIS-5372: 24.August.2015 43
In Real Life
Alice
Bob
Malory
K - secret
Cannot Decrypt C !
M = Hi, A, B, “attack tomorrow”
C = E(K, M)
Intercept 2
K - secret
C’ 3
Cannot Produce C’ !
C’ = E(K, “Hi, A, B, postpone attack”)
![Page 44: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/44.jpg)
CIS-5372: 24.August.2015 44
Objective:
Recover message given ciphertext
Recover key – more significant – why ?
General approaches:
Cryptanalytic attack
Brute-force attack
If either succeed all key use compromised
Cryptanalysis
![Page 45: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/45.jpg)
CIS-5372: 24.August.2015 45
Ciphertext only
Only know algorithm & ciphertext
Assume you know or can identify plaintext
Known plaintext
Know/suspect plaintext & ciphertext
How ?
Perhaps know some protocol
Cryptanalytic Attack
![Page 46: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/46.jpg)
CIS-5372: 24.August.2015 46
Chosen plaintext
Select plaintext and obtain ciphertext
Example: Encrypt 0
Encrypt 1
Encrypt 01, 10, etc
Chosen ciphertext
Select ciphertext and obtain plaintext
Chosen text
Select plaintext or ciphertext to en/decrypt
Cryptanalytic Attack (cont’d)
![Page 47: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/47.jpg)
CIS-5372: 24.August.2015 47
Always possible to simply try every key
Work is a function of key size Given cipertext
1. Try every key until decryption is intelligible
2. Assume either know / recognise plaintext
Use cloud computing for parallelism
Use volunteer computing
SETI@Home, Folding@Home, Large prime search, RSA challenge
Cryptanalysis – Brute Force
![Page 48: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/48.jpg)
CIS-5372: 24.August.2015 48
Key Size (bits) Number of Alternative
Keys
Time required at 1
decryption/µs
Time required at 106
decryptions/µs
32 232 = 4.3 109 231 µs = 35.8 minutes 2.15 milliseconds
56 256 = 7.2 1016 255 µs = 1142 years 10.01 hours
128 2128 = 3.4 1038 2127 µs = 5.4 1024 years 5.4 1018 years
168 2168 = 3.7 1050 2167 µs = 5.9 1036 years 5.9 1030 years
26 characters
(permutation)
26! = 4 1026 2 1026 µs = 6.4 1012 years 6.4 106 years
Brute Force Speed
Key size is essential !
Moore’s law:
As computers get faster, old ciphertexts become vulnerable
![Page 49: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/49.jpg)
CIS-5372: 24.August.2015 49
Most significant advance in the 3000 year history of cryptography !
Uses two keys – a public and a private key
Asymmetric: parties are not equal
Public Key Cryptosystems (PKC)
Public invention Whitfield Diffie & Martin Hellman at Stanford University in
1976
Known earlier in classified community
![Page 50: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/50.jpg)
CIS-5372: 24.August.2015 50
Addresses two key issues:
Key distribution – how to have secure communications in general without having to trust a KDC with your key
Digital signatures – how to verify a message comes intact from the claimed sender
Why Public Key ?
![Page 51: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/51.jpg)
CIS-5372: 24.August.2015 51
PKC in a Nutshell
Plaintext
Encryption
Algorithm
Encryption Key Decryption Key
Plaintext
Decryption
Algorithm
![Page 52: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/52.jpg)
CIS-5372: 24.August.2015 52
PKC in Real Life!
Alice
Bob
Malory
C= Encrypt(pubKeyB, M) 1
pubKeyB - public
privKeyB - private
pubKeyB - public
Cannot Infer privKeyB
from pubKeyB !
Intercept C 2
Cannot Obtain M !
M= Decrypt(privKeyB, C)
Has message M
![Page 53: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/53.jpg)
CIS-5372: 24.August.2015 53
Unconditional security
No matter how much computer power or time is available, the cipher cannot be broken
The ciphertext provides insufficient information to uniquely determine the corresponding plaintext
Computational security
Given limited computing resources (e.g., time needed for calculations is greater than age of universe), the cipher cannot be broken
More Definitions
![Page 54: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/54.jpg)
CIS-5372: 24.August.2015 54
Building blocks that we will define and use in the next lectures
Will describe in more detail in class 5, 6, 7
Encryption
Signature
Hash
Crash Course in Crypto
![Page 55: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/55.jpg)
CIS-5372: 24.August.2015 55
Verify author, date & time of message
Authenticate message contents
Verifiable by third parties to resolve disputes
Digital Signatures
![Page 56: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/56.jpg)
CIS-5372: 24.August.2015 56
Digital Signature Model
Plaintext
Signature
Algorithm
Private Key
Public Key
Verification
Algorithm
Plaintext
Valid !
Invalid !
Signature
![Page 57: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/57.jpg)
CIS-5372: 24.August.2015 57
In Real Life
Alice
Bob
Malory
pubKeyB - public
privKeyB - private
pubKeyB - public
Cannot Forge
Bob’s Signature !
M = I owe Alice $1000
S = Sign(M, privKeyB)
M, S
Verify(M, S, pubKeyB) = true !
Intercept 2
M’ = I owe Malory $1000
for same S
M’ = I owe Malory $1000
for new S’
![Page 58: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/58.jpg)
CIS-5372: 24.August.2015 58
In Real Life
Alice
Bob
pubKeyB - public
privKeyB - private
pubKeyB - public
Bob Cannot Deny
Signature S !
M = I owe Alice $1000
S = Sign(M, privKeyB)
M, S
Verify(M, S, pubKeyB) = true !
![Page 59: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/59.jpg)
CIS-5372: 24.August.2015 59
Depend on the message signed
Use information unique to sender
Prevent both forgery and denial
Easy to generate
Easy to verify
Computationally infeasible to forge
New message for existing digital signature
Fraudulent digital signature for given message
Digital Signature Requirements
![Page 60: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/60.jpg)
CIS-5372: 24.August.2015 60
Building blocks that we will define and use in the next lectures
Will describe in more detail in class 5, 6, 7
Encryption
Signature
Hash
Crash Course in Crypto
![Page 61: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/61.jpg)
CIS-5372: 24.August.2015 61
Condenses message M to fixed size
h = H(M)
Hash Functions
M (L bits)
Hash H
Hash value h
(fixed length)
Assume hash function is public
Used to detect changes to message
Looks Random !
![Page 62: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/62.jpg)
CIS-5372: 24.August.2015 62
Hash Properties
Pre-image resistance:
Given value h, hard to find message M such that h = H(M)
Second pre-image resistance:
Given message M1, hard to find M2 such that H(M1)=H(M2)
Collision resistance:
Hard to find any M1 and M2 such that H(M1)=H(M2)
![Page 63: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/63.jpg)
CIS-5372: 24.August.2015 63
Building blocks that we will define and use in the next lectures
Will describe in more detail in class 5, 6, 7
Encryption
Signature
Hash
Crash Course in Crypto
![Page 64: Cis5372 1 Intro](https://reader034.vdocument.in/reader034/viewer/2022050721/563dbb12550346aa9aaa0829/html5/thumbnails/64.jpg)
CIS-5372: 24.August.2015 64
Administrative Issues
Rules of the Class
Class Overview
Information Assurance Overview
Outline