DIGITAL INFORMATION SECURITY TECHNOLOGY
전자정보 보안기술
2019 Spring Semester Instructor: Jaewoo Lee
Some Slides from “Security Engineering”,Ross, 2008
Today Lecture
• Review
• Ch. 6: Distributed Systems
• Network Security
• Distributed Systems Security
Review: RSA
• Bob generate RSA key
• large primes p=61, q=53
N=pq=3233, (p-1)(q-1)=3120
• Find e which is relative prime (서로소) to (p-1) and (q-1)
1<e<3120 e=17
• Find d s.t. e*d mod (p-1)(q-1)=1 d=2753
• Public key: (N, e), Private key: d
Bob post public key (3233,17) and keep private key 2753
• Alice want to send msg to Bob
• Alice get Bob’s public key in his homepage
• Alice encrypt P (=65)
• Alice send C to Bob
• Bob decrypt C
6517 mod 3233=2790 27902753 mod 3233 = 65
Network Security
• To prevent resources and networks of organization from attack
• Network Separation (망분리)
• Separate inner network from outer network
OSI 7 layer
• OSI 7 layer
• Interconnect heterogeneous network
• Simplification, Standardization, Modularization
P2P
Multi-hop
Ethernet HW, Lan Cable Reliable Connection
HTTP, FTP Open System Interconnection
Data Link Layer
• MAC address
• Ethernet HW address (48bit)
• Vendor ID (3byte)+
Host ID (3byte)
• HEX(16진수) notation
• IP address (IPv4)
• A numerical label to the device in WWW
• 32bit (4byte)
• dot-decimal notation
• ARP
• A protocol mapping between MAC address and IP address
Media Access Control
Internet Protocol
Address Resolution Protocol
TCP/IP
OSI 참조모델 계층 TCP/IP 계층 Application
Application layer Presentation layer
Session layer
Application
layer Application
Protocol & service
Transport layer Transport layer TCP UDP
Network layer Internet layer IP ICMP ARP RARP 경로배정 protocol Data link layer Network
Interface layer Network driver software Physical layer Hardware NIC(Network interface card)
ICMP: Internet Control Message Protocol IGMP: Internet Group Management Protocol
상위계층
하위계층 IGMP IGMP
Transport layer protocol: TCP vs UDP
TCP UDP
Transport type Connection Connectionless
Connection Setup Connect (3way handshaking)
Disconnect (4way handshaking)
No connection setup
Reliability High Low
Speed Slow Fast
Influence to upper layers X need to handle End-To- End errors
Q. Which protocol does YouTube use?
Transmission Control Protocol User Datagram Protocol
3 Way Handshaking (Connect)
Related to IP spoofing, Session Hijacking
Distributed Systems
• Distributed Systems
• A set of computers that cooperate for common goals
• E.g., wireless sensor networks, world wide web (WWW)
Concurrency (Ch. 6.1)
• Processes are concurrent
• They run at the same time
• Concurrency increasing
1) Growing online business
2) Complex devices
Using old data
• Replay Attack (Ch. 3)
• ‘grabber’ example
• Race Condition Attack (Ch. 4)
• ‘mkdir’ example
• Time of Check To Time Of Use (TOCTTOU) attack
• Bugs caused by changes between the condition check and the use of the results of that check
• Bank example (balance: $3000)
Check Balance
Withdraw $2000 Deposit $1000
Check Balance Withdraw $2000
Deposit $1000
(Normal) (Under Attack)
The order of update
• Bank example
• Balance: $1000
Deposit $5000
Withdraw $2000
Deposit $5000
Withdraw $2000
(Normal)
(Under Attack)
Sol 1: process transaction based on the arrival time Sol 2: log-based update
