Transcript Chapter 9, Security Modern Operating Systems by

Chapters 9 & 10,
Modern Operating Systems
by A. S. Tanenbaum
IA 705, Prof. Brown, Spring 2003
Group E
IA705, Spring 2003
J. Paloschavez, M. Troxler, J. Boggs,
J. Lagas Chapters 9 & 10 IA705
1
Chapter 9, UNIX & Linux
Modern Operating Systems
by A. S. Tanenbaum
Group E
IA705, Spring 2003
J. Paloschavez, M. Troxler, J. Boggs,
J. Lagas Chapters 9 & 10 IA705
2
Jose Paloschavez
J. Paloschavez, M. Troxler, J. Boggs,
J. Lagas Chapters 9 & 10 IA705
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The Security Environment
Threats
Security goals and threats
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Intruders
Common Categories
1. Casual prying by nontechnical users
2. Snooping by insiders
3. Determined attempt to make money
4. Commercial or military espionage
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Accidental Data Loss
Common Causes
1. Acts of God
-
fires, floods, wars
2. Hardware or software errors
-
CPU malfunction, bad disk, MSFT program bugs
3. Human errors
-
data entry, wrong backup disk
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Basics of Cryptography
Relationship between the plaintext and the ciphertext
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Secret-Key Cryptography
• Monoalphabetic substitution
– each letter replaced by different letter
Plaintext:
ABCDEFGHI…
Ciphertext: EQHOZGS EGSSTUT
CAPITOL COLLEGE
• Given the encryption key,
– easy to find decryption key
• Secret-key crypto called symmetric-key crypto
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Public-Key Cryptography
Private Key
Mathematically
Linked
Key Pair
Public Key
• All users pick a public key/private key pair
– publish the public key
– private key not published
• Public key is the encryption key
– private key is the decryption key
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J. Lagas Chapters 9 & 10 IA705
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One-Way Functions
• Function such that given formula for f(x)
– easy to evaluate y = f(x)
• But given y
– computationally infeasible to find x
• Many names
– Compression function, contraction function,
message digest, fingerprint, cryptographic
checksum or manipulation detection mode (MDC)
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Digital Signatures
• Signature is authentic
• Signature is unforgeable
• Signature is not reusable
• Signature is unalterable
• Signature cannot be
repudiated
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User Authentication
Authentication must identify:
1. Something the user knows
2. Something the user has
3. Something the user is
NOTE: This is done before user can use the
system
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Authentication Using Passwords
LOGIN: jose
PASSWORD: AuthEnt
SUCCESSFULL LOGIN
(a)
LOGIN: bogs
INVALID LOGIN NAME
LOGIN
(b)
LOGIN: lagas
PASSWORD: Iforgot
INVALID LOGIN
LOGIN:
(c)
(a) A successful login
(b) Login rejected after name entered
(c) Login rejected after name and password typed
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Authentication Using Passwords
Jose, 2918, b(13%%BeTWW2918)
Matt, 9282, e(WonderDog9282),
James, 9619, e(AxC@Oczw9619)
John, 3168, e(MonkeyBusiness,3168)
,
,
,
Lewes, 1705, e(ShenTel,1705)
Salt
Password
The use of salt to defeat precomputation of
encrypted passwords
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Improving Password Security
1. Password should be a minimum of, seven characters
, lower case letters.
2. Passwords should contain both UPPER and
3. Passwords should contain at least one digit or, spec*al.
,
4. Passwords should not be dictionary words, names, etc.
5. Passwords should be treated like a toothbrush, not shared.
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Authentication Using a Physical Object
• Magnetic cards
– magnetic stripe cards
– chip cards: stored value cards, smart cards
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Authentication Using Biometrics
A device for authenticating using iris
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Matt Troxler
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Attacks from the Inside
•
•
•
•
•
Trojan Horses
Login Spoofing
Logic Bombs
Trap Doors
Buffer Overflow
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Design Principles for Security
• Public Design - easier to service.
• Default = Deny Access - easier to trace
errors.
• Check access occasionally, not just a login
or file open procedure
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Design Principles Cont’d.
• Minimal permissions for all users/processes
• Ease of use - difficult interfaces usually
result in wide-open environments
• Keep it simple - tight and efficient code is
easy to review and lock down
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External Attacks (Viruses)
How they function
• “Dropper” tool is used to deploy a virus
• Infected file is distributed (preferably
publicly)
• Users go get (or receive unknowingly) and
install the infected file
• Payload of the file runs, does whatever the
virus does
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Classifications of Viruses
• Companion virus - runs
in place of a legitimate
file
• Executables - virus code
imbeds itself in another
.exe (overwriting)
• Parasitic viruses overwriting, but the
original files still work
after infection.
• Cavity virus - virus
embeds itself in unused
portions of legit. files
• Memory Resident - Lives
in memory, little disk
activity
• Boot Sector - lives at the
first sector of the HDD
• Device Driver - gets
loaded as a legit. file in
kernel mode
• Macro - attached to a file
that appears innocent
• Source Code - requires
some knowledge of
programming
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How Viruses Spread
• Downloads
• Email
• Storage Space (fixed or removable disks,
memory, etc.)
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Antivirus and Anti-Antivirus…
and so on…
• Date hiding – Date
disguising – Parent
folder…
• Size hiding –
Compression
• Bitwise hiding –
Look for decryption
routine/key
Polymorphic
– Look for
morphing
routine code
Checksums
– Delete or
overwrite –
Encrypt
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Securing Mobile Code
• Sandboxing
• Interpretation
• Code
• Java Security
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Protection Mechanisms
• Protection Domains
• Access Control Lists
• Capabilities
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Trusted Systems and Multilevel
Security
•
•
•
•
•
•
Trusted Computing Base
Formal Models
Bell-La Padula Model
Biba Model
Orange Book
Covert Channels
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Chapter 10, UNIX & Linux
Modern Operating Systems
by A. S. Tanenbaum
Group E
IA705, Spring 2003
J. Paloschavez, M. Troxler, J. Boggs,
J. Lagas Chapters 9 & 10 IA705
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Jim Boggs
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J. Lagas Chapters 9 & 10 IA705
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History
•
•
•
•
•
•
UNICS
PDP-11 UNIX & Portable UNIX
Berkeley UNIX
Standard UNIX & POSIX
MINIX
Linux
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Overview of UNIX
UNIX Goals & Interfaces
• Goals
– Handle Multiple Processes & Users
– Design Principles
• Interfaces
User Interface
Library Interface
System Call Interface
Users
Utility Programs
Standard Library
UNIX OS
Hardware
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User Mode
Kernel Mode
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Overview of UNIX
UNIX Shell & Utility Programs
• Shell
–
–
–
–
Ordinary program providing command line interface
Standard input/output
Flexibility (wild cards, standard I/O,flags, pipes)
Shell Scripts
• Utility Programs
–
–
–
–
File & Directory Commands
Filters
Development Tools & Text Processing
System Administration
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Overview of UNIX
Kernel Structure
Kernel structure graphic, copyright Prentice-Hall 2001, Modern Operating Systems, p. 688
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Processes in UNIX
Concepts and Process Management
• Active Entities are Processes
–
–
–
–
Foreground & Background
Parent & Child
ID for Each
Single & Multiple Threads
• Process Management System Calls
– Means for Processes to Communicate
– Based on POSIX
– Examples
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Processes in UNIX
Implementation
• Process Table
–
–
–
–
Scheduling Parameters
Memory Image
Signals
Miscellaneous
• Use Structure
–
–
–
–
–
Machine Registers
System Call State
File Descriptor
Accounting
Kernel Stack
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Processes in UNIX
Threads
• UNIX
– Supported in Kernel, but Process-oriented
– Difficult Thought Process in Using Multiple Threads
• Fork & other Examples
• Linux
–
–
–
–
Kernel-oriented
Clone
Detailed Sharing
Non-portability
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Processes in UNIX
Scheduling
• UNIX
– Designed for Response to Interactive Processes
– Process-oriented Queue Management
– Get Processes Rapidly out of the Kernel
• Linux
– Thread-oriented
– Classes of Linux Threads
• Real-time FIFO
• Real-time Round Robin
• Timesharing
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Processes in UNIX
Booting UNIX
•
•
•
•
Get Kernel Running
Set Message Buffer
Allocate Kernel Data Structure
System Configuration (drivers)
– Static Links
– Dynamic Loads
• Begin Process 0
• Init
• Login
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John Lagas
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Unix Memory Management
• Fundamental Concepts
– Text
– Data
– Stack
– Shared Text Segments
– Memory-mapped files
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Unix Memory Management
• Memory Management System Calls
– brk
– mmap
– unmap
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Unix Memory Management
• Implementation
– Swapping
– Paging
– Page replacement algorithm
• Two-handed
• Clock
– Memory Management under Linux
• Buddy algorithm
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Unix I/O
• Fundamental concepts
– Special files
– Character special
– Block special
• Major and minor numbers
– Networking
• Sockets
• TCP/UDP and IP
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Unix I/O
• System Calls
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Unix I/O
• Implementation
– Ioctl
• Device dependant
• Device drivers
– Streams
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Unix File Systems
• Fundamental Concepts
– “Standard” directories
• bin, dev, etc, sbin, lib, usr
– path
• absolute and relative
– linking files
– locking
• Prevents overwrites
– File descriptor and file handle
• Descriptor is of type “int”
• Handle is the “name of the file”
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Unix File Systems
• System Calls
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Unix File Systems
• Implementation
– Superblock
– Inodes
– Inode table
– What info to keep for a file?
•
•
•
•
DAC
MAC
Access/mod/change times
UID/GID
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Unix File Systems
• NFS
– Architecture
– Client-server
• Makes remote file system appear local
• Can cause system to “hang”
– Implementation
• Local is of type NFS
• Remote is not relevant for the client
– The server handles those details
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Unix Security
• Fundamental concepts
– UID and GID
• Mentioned above under File systems
– DAC and mode bits
• Extended mode bits
– Superuser !!! Got root?
• UID 0
• Only one per system, or game over…
– EUID
• Who are you running as???
• SETUID / SETGID
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Unix Security
• System Calls
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Unix Security
• Implementation
– The devil is in the details
– System files
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Questions and Answers
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