1 security (datensicherheit) chapter 9 9.1 the security environment 9.2 basics of cryptography 9.3...
TRANSCRIPT
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Security(Datensicherheit)
Chapter 9
9.1 The security environment 9.2 Basics of cryptography 9.3 User authentication 9.4 Attacks from inside the system 9.5 Attacks from outside the system 9.6 Protection mechanisms 9.7 Trusted systems
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Ziele und Bedrohungen
ZieleVertraulichkeitIntegritätVerfügbarkeitVerbindlichkeitAnonymitätAuthentizitätZugriffsbeschränkung
Bedrohungen–Höhere Gewalt
• Feuer, Wasser, Blitz,Naturkatastrophen, Krankheit
–Organisatorische Mängel• Fehlende Regelungen und
Betriebsmittel–Fehlhandlungen
• Unbewußte Passwortpreisgabe,• Unbeabsichtigte Beschädigungen
–Technisches Versagen• Ausfälle• Fehlverbindungen• Softwarefehler, Schwachstellen• Verdeckte Kanäle
–Vorsätzliche Handlungen
Dienste,Mechanismen undManagement
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Bedrohungen• Vorsätzliche Handlungen
– Klassische Delikte• Diebstahl, Einbruch, Vandalismus,
Sabotage(neu: gestohlene Laptops)
– Klassische Spionage• Abhören, Ausspähen
(neu: IT-Industriespionage)
– IT - und Netz - Intrusions• Manipulation, Sabotage• Auftragsüberflutung• Abhören, Ressourcen-Zugriffe• Flußanalyse• Zugriffe auf verdeckte Kanäle• Paßwortausspähen• Kryptoanalyse• Maskerade• Viren, Bomben,
Trojanische Pferde, Würmer, Hintertüren
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BedrohungenAnsatzpunkte• An Nutzer-Stelle treten• Schwachstellen ausnutzen
– Planung und Administration• Kontroll-Lücken• schwache Kontrolle
– Software und Protokolle• Entwurfsfehler• Programmierfehler• Bombe• Hintertür
– benutzte Dienste• DNS• Authentifikation
• Zugang / Zugriff erzwingen– Einbruch / Diebstahl– Anzapfen
• Fortpflanzung im Netz
Angriffsmuster• Host-Angriff
– Aushorchen und Ausspähen– Maskerade– Einschleusen von Angriffs-SW– Abhören / Auslesen /
Manipulation von BM und BS– Zerstörung
• Netz-Angriff– Erkundung– Abhören / Abfangen /
Einspielen– Maskerade / Spoofing– Wiedereinspielen / Replay– Ersetzen von Komponenten
und Diensten– Stören von Komponenten– Last-Erzeugung
Host
Anwendung
System
Router
System
Dienst
Nutzer
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AngriffssoftwareQuellen
Dokumente / Programme per
• Datenträger
• Download
• E-Mail-Anhang
• Aktive WWW-Inhalte
• Fern-Administration
Wirkungen
• Bombe
• Hintertür
• Trojanisches Pferd
• Stützpunkt
Fortpflanzung
• im Host: Virus
• im Netz: Wurm
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Angriffswerkzeuge
Tools• im WWW abrufbar• Hacker-Knowhow für alle• Automatisierung
• Scanner– Ports und Systeme– Verzeichnisse
• Sniffer– IP-Pakete, TCP-Verbindungen– Sitzungen
• Attack– Raten und Probieren– Schwachstellen-Angriffe (z.B.
Sendmail Puffer-Überlauf)– Produkt-Angriffe (z.B. Hacking
Novell Netware)– Verteilte DoS-Angriffe
• Support– Passwort-Cracker– Passwort-Listen– Hacker-Informationssysteme
PotentiellerAngreifer
Ziel
Anwendung
System
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Maßnahmen
• Infrastruktur
– Gebäudetechnik, Lagerung und Versorgung
• Organisation
– Verfahren und Regelungen
– Zuständigkeiten und Aufgaben
– Beratung, Betreuung, Kontrolle
– Dokumentation
Personal
– Qualifikation
– geregelte Übergaben und Zuständigkeiten
– Vertrauenswürdigkeit Notfallvorsorge
– Regelungen, Übungen
– Ersatz, Ersatzvereinbarungen
– Aufbewahrung Maßnahmen in Hard-,
Software und Kommunikationseinrichtungen
Bequemlichkeit und Nachlässigkeit Automatisierung und Zwang
Datenschutz und Betriebsverfassung
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Sicherheitsdienste• Authentifikationsdienste
• Autorisierungsdienste
• Vertraulichkeitsschutzdienste
• Integritätsdienste
• Verfügbarkeitsschutzdienste
• Verbindlichkeitsdienste
– Signaturzertifizierungs- undAuskunftsdienste
• Zahlungsdienste
• Produktzertifizierungsdienste
• Mehrseitige Sicherheit– Nutzer– Arbeitgeber– Geschäftspartner– Kunden
– TK-Provider– Produktlieferant
– Staat– Gesellschaft
– ……
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Sicherheitsmechanismen• Systembeobachtung und Prüfung
• Schwachstellenermittlung
• Zugangs-, Zugriffs- und Verkehrskontrolle
• Ausweisfunktionen
• Proaktive Systemänderungen
– z.B. Passwortwechsel
• Vertrauenswürdige 3. Parteien
• Kryptosysteme
• Zahlungssysteme
• Leistungsbeschränkungen
• Redundanz
– Server, Kommunikation
– Speicher, Daten, Backup
• Vernebeln und Ablenken• Sichere Kommunikationsprotokolle• Authentifikations- und
Schlüsselverteilprotokolle• Sicherheitsklassifikation und
Produktzertifizierung• Spezialhardware
– Logplatten, Chipkarten, Kryptoboxen
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SchutzPlanung und Administration• Enger Spielraum
– Zugangskontrolle– Zugriffskontrolle– Authentifikation– Verkehrskontrolle
• Überwachung– Monitoring– Logs und Audits
• Schwachstellen-Analyse• Systempflege
Schutz-Systeme
• Schwachstellen-Analysatoren
• Kontrolldienste
– Autorisierung und Authentifikation
• Inhaltsfilterung und Prüfung
– Virenscanner
• Verkehrsfilter
– Firewalls
• Abschottung
– Kryptokanäle, Tunnels
– VPNs
• Überwachung
– Intrusion Detection Systeme
– Fallstrick- undTeergruben-Systeme
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Basics of Cryptography
Relationship between the plaintext and the ciphertext
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• Monoalphabetic substitution– each letter replaced by different letter
• Given the encryption key, – easy to find decryption key
• Secret-key crypto called symmetric-key crypto
Secret-Key Cryptography
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Public-Key Cryptography
• 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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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
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Digital Signatures
• Computing a signature block
• What the receiver gets
(b)
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User Authentication
Basic Principles. Authentication must identify:
1. Something the user knows
2. Something the user has
3. Something the user is
This is done before user can use the system
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Authentication Using Passwords
(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
• How a cracker broke into LBL– a U.S. Dept. of Energy research lab
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Authentication Using Passwords
The use of salt to defeat precomputation of encrypted passwords
Salt Password
,
,
,
,
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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 measuring finger length.
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Countermeasures
• Limiting times when someone can log in
• Automatic callback at number prespecified
• Limited number of login tries
• A database of all logins
• Simple login name/password as a trap– security personnel notified when attacker bites
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Operating System SecurityTrojan Horses
• Free program made available to unsuspecting user– Actually contains code to do harm
• Place altered version of utility program on victim's computer– trick user into running that program
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Login Spoofing
(a) Correct login screen(b) Phony login screen
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Logic Bombs
• Company programmer writes program– potential to do harm– OK as long as he/she enters password daily– ff programmer fired, no password and bomb explodes
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Trap Doors
(a) Normal code. (b) Code with a trapdoor inserted
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Buffer Overflow
• (a) Situation when main program is running• (b) After program A called• (c) Buffer overflow shown in gray
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Generic Security Attacks
Typical attacks• Request memory, disk space, tapes and just read• Try illegal system calls• Start a login and hit DEL, RUBOUT, or BREAK• Try modifying complex OS structures• Try to do specified DO NOTs• Convince a system programmer to add a trap door• Beg admin's sec’y to help a poor user who forgot password
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Famous Security Flaws
The TENEX – password problem
(a) (b) (c)
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Design Principles for Security
1. System design should be public
2. Default should be n access
3. Check for current authority
4. Give each process least privilege possible
5. Protection mechanism should be- simple
- uniform
- in lowest layers of system
6. Scheme should be psychologically acceptable
And … keep it simple
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Network Security
• External threat– code transmitted to target machine– code executed there, doing damage
• Goals of virus writer– quickly spreading virus– difficult to detect– hard to get rid of
• Virus = program can reproduce itself– attach its code to another program– additionally, do harm
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Virus Damage Scenarios
• Blackmail
• Denial of service as long as virus runs
• Permanently damage hardware
• Target a competitor's computer– do harm– espionage
• Intra-corporate dirty tricks– sabotage another corporate officer's files
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How Viruses Work (1)
• Virus written in assembly language
• Inserted into another program– use tool called a “dropper”
• Virus dormant until program executed– then infects other programs
– eventually executes its “payload”
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How Viruses Work (2)
Recursive procedure that finds executable files on a UNIX system
Virus couldinfect them all
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How Viruses Work (3)
• An executable program• With a virus at the front• With the virus at the end• With a virus spread over free space within program
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How Viruses Work (4)
• After virus has captured interrupt, trap vectors• After OS has retaken printer interrupt vector• After virus has noticed loss of printer interrupt vector and recaptured it
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How Viruses Spread
• Virus placed where likely to be copied
• When copied– infects programs on hard drive, floppy– may try to spread over LAN
• Attach to innocent looking email– when it runs, use mailing list to replicate
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Antivirus and Anti-Antivirus Techniques
(a) A program(b) Infected program(c) Compressed infected program(d) Encrypted virus(e) Compressed virus with encrypted compression code
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Antivirus and Anti-Antivirus Techniques
Examples of a polymorphic virus
All of these examples do the same thing
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Antivirus and Anti-Antivirus Techniques
• Integrity checkers• Behavioral checkers• Virus avoidance
– good OS– install only shrink-wrapped software– use antivirus software– do not click on attachments to email– frequent backups
• Recovery from virus attack– halt computer, reboot from safe disk, run antivirus
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The Internet Worm
• Consisted of two programs– bootstrap to upload worm– the worm itself
• Worm first hid its existence
• Next replicated itself on new machines
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Mobile Code (1) Sandboxing
(a) Memory divided into 1-MB sandboxes
(b) One way of checking an instruction for validity
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Mobile Code (2)
Applets can be interpreted by a Web browser
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Mobile Code (3)
How code signing works
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Java Security (1)
• A type safe language– compiler rejects attempts to misuse variable
• Checks include …1. Attempts to forge pointers2. Violation of access restrictions on private class members3. Misuse of variables by type4. Generation of stack over/underflows5. Illegal conversion of variables to another type
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Java Security (2)
Examples of specified protection with JDK 1.2
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Protection Mechanisms Protection Domains (1)
Examples of three protection domains
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Protection Domains (2)
A protection matrix
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Protection Domains (3)
A protection matrix with domains as objects
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Access Control Lists (1)
Use of access control lists of manage file access
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Access Control Lists (2)
Two access control lists
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Capabilities (1)
Each process has a capability list
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• Cryptographically-protected capability
• Generic Rights1. Copy capability
2. Copy object
3. Remove capability
4. Destroy object
Capabilities (2)
Server Object Rights f(Objects, Rights, Check)
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Trusted SystemsTrusted Computing Base
A reference monitor
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Formal Models of Secure Systems
(a) An authorized state
(b) An unauthorized state
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Multilevel Security (1)
The Bell-La Padula multilevel security model
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Multilevel Security (2)
The Biba Model
• Principles to guarantee integrity of data
1. Simple integrity principle• process can write only objects at its security level or lower
2. The integrity * property• process can read only objects at its security level or higher
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Orange Book Security (1)
• Symbol X means new requirements• Symbol -> requirements from next lower category apply here also
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Orange Book Security (2)
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Covert Channels (1)
Client, server and collaborator processes
Encapsulated server can still leak to collaborator via covert
channels
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Covert Channels (2)
A covert channel using file locking
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Covert Channels (3)• Pictures appear the same
• Picture on right has text of 5 Shakespeare plays– encrypted, inserted into low order bits of color values
ZebrasHamlet, Macbeth, Julius CaesarMerchant of Venice, King Lear