iv. network security - ensimagensiwiki.ensimag.fr/images/5/5e/network_security_-_4...27 4mmsr -...

•  Lecturers: Fabien Duchene, Dominique Vicard •  Chapters:

•  IV.6. Internet

4MMSR - Network security course

IV. Network Security

2010-2011

Grenoble INP Ensimag

Plan – thème IV. La sécurité des réseaux

•  4. Intranet •  Authentification

Active Directory, Kerberos

•  Conformance (IDS/IPS, Antimalware, NAC)

•  5. Protocoles •  RFID •  RAS: PPTP, L2F, L2TP •  RADIUS •  802.1x – wifi •  IPSec •  SSL/TLS •  VPN •  GSM

•  6. Internet •  Firewall •  Proxy, Socks •  Web-Services •  PKI

•  7. Browser •  Privacy mode •  Javascript, XSS •  Flash, ActiveX, Java •  Sandbox •  HTLM5

o  0. Introduction o  Le réseau o  Parano: mode d’emploi

o  1. Menaces, vuln., attaques o  Définitions o  Attaques

o  2. Qqes algorithmes o  Stéganographie o  Partage de secret o  P2P: l’algo. Eigentrust

o  3. Poste client o  Certifications o  Principes de la sécurité o  Principaux méchanismes o  NT4+ o  Unix

0.1. Introduction 4MMSR - Network Security - 2010-2011 2

IV. 6. Internet

3 4MMSR - Network Security - 2010-2011

•  Firewall •  Proxy, Socks •  Web-Services •  PKI

6.1. Firewall

•  Introduction •  Firewall locations

o  Network edge o  Endpoint & servers

•  Packet filtering •  Stateful Packet Inspection •  Application firewalls •  Firewall policy

Some stuff from Cyril Voisin’s lecture: “Base de la sécurité des réseaux", Principal Security Advisor, Microsoft

6.1.1. Perimeter security

•  Security at the network layers (transport & network) •  Part of the in-depth defense mechanism •  Traditional security view

•  But! •  Old, traditional mechanism •  This is NOT SUFICIENT today: a host protection is vital! •  Lack of flexibility, cost

o  Microsoft now pushes for a “deperimeterization”: IPSec boundaries

6.1.1. Firewall - introduction

•  Filtering •  “limits network access between at least two

networks” o  2 directions filtering o  Rules, metrics o  RFC2979

•  thus located between two networks o  L2 switching capabilities o  L3 router in an IP path

•  Information Disclosure prevention: •  IPv4 network: Network Address Translation protects a

network topology from being discovered o  1-to-1 mapping o  1-to-N mapping (discrimation regarding destination port)

6.1.1. Firewall – introduction (2)

•  Products •  Software firewall

o  Installable executable –  linux iptables –  Windows Advanced Firewall

o  Virtual machine

•  Hardware accelerated firewall “appliance” = HW+SW o  Eg: Juniper, NetASQ !

6.1.2. Firewall locations

•  Endpoint & servers “host-based firewall” •  Software: in-depth defense principle! •  Tight OS interactions (each socket or routing operation!) •  Easier to hack than separate firewalls

•  Network Edge o  Software o  Virtualized o  Hardware

Firewall WAN (public network) LAN

(controlled network)

Picture source: Wikipedia

DMZ (DeMilitarized Zone) "perimeter network"

•  Two firewall levels •  the multiculture principle => different brands

•  One firewall level:

6.1.2. some common DMZ network topologies

!"#$%"$#&'()&

!"#$%"$#&

!"#$%"*+&"$#,-%.&

6.1.3. Stateless firewalls “packet filtering”

•  1st generation: o  1988 Dodong Sean James, Elohra (DEC) o  1980-1990 Bill Cheswick and Steve Bellovin (AT&T

Bell Labs)

•  Filter packets for allowing some circuits: o  Pass o  Drop (silently discard) o  Reject (error response to the sender)

•  Depending of L3 (Network) and L4 (Transport) metrics o  IP source/dest address o  TCP/UDP source/dest port number

•  Policy example: o  allow TCP->21 traffic from networkA to network B o  deny all traffic from (any network) to (any network)

!""#$%&'(#$)%/*00+12*3-"4&5$551-"4&

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.#-/,$0&/!97&

12+0%/$#<$%"$#7&

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6.1.4. Stateful packet inspection “session filtering”

•  Attacks on 1st generation FW: o  DoS: eg: SYN flood (firewall ressources consumption)

•  2rd generation o  1989-90: Janardhan Sharma, Dave Presetto, and Kshitij Nigam o  1995: first commercial product by Nir Zuk’s team (CheckPoint)

•  Stores the “connection state” o  is that new packet conform to that current connection? o  or is it for a new connection? o  see the NAT connection table (in your network lecture !)

•  Additional conformance verification for: o  TCP flags (SYN, ACK, RST, PSH, FIN) o  Session state and the TCP sequence number! o  If any packet does not correspond to the expected state, it is

blocked!

6.1.4. Stateful firewalls – TCP states

13 4MMSR - Network Security - 2010-2011 http://en.wikipedia.org/wiki/Transmission_Control_Protocol

6.1.4. Stateful firewalls – state table

•  Statically limited size table •  Each entry:

•  Flushing policy: if the connection is closed, or if no packet is sent during the TIMEOUT time

•  Some Internet Protocol numbers:

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3$,-,5,&%!"#$"%%&'()

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:3%+7;<#$% :3%+';#%

>& !;(9&

B& :;9&

>I& 8'9&

http://en.wikipedia.org/wiki/List_of_IP_protocol_numbers

Understanding the FW-1 State Table, Lance Spitzner

6.1.4. SPI firewall - example

•  Eg: web-server (HTTP on TCP 80) publishing over IPv4, protected by D-NAT (Destination NAT) in that case in 1-to-1 mapping

SPI Firewall Web Client 87.98.190.108 10.0.0.4/28

. Web-Server (listening on TCP

Public IP addresses

91.121.51.205

G-J%2$9-%#K&:;9&@=ID@&'$53"*3-"9-%#K&:;9&DE&

G-J%2$!9K&DICFD6&'$53"*3-"!9KF>C>A>6&

GL9-%#K&:;9&@=ID@&'L9-%#K&:;9&DEDA&

GL!9K&DI6&'L!9K&>ECECEC=&

GL9-%#K&:;9&DEDA&'L9-%#K&:;9&@=ID@&

GL!9K&>ECECEC=&'L!9K&DI6&

6=.%>?@%

GL9-%#K&:;9&DE&'L9-%#K&:;9&@=ID@&GL!9K&F>C>A>C=>CAE=&

'L!9K&DI6&

6=.%>?@%

SYN processing

The client can now send its HTTP requests and the same kind of checks are performed during the WHOLE communication

6&>?@% 6&>?@% AA%AH%

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6.1.5. Application firewalls

•  3nd generation o  1990-91: Bill Cheswick (AT&T), Marcus Ranum, and

Gene Spafford (Purdue)

•  Has a “protocol description” o  Sequences, data types & size : eg: HTTP, DNS !

•  QoS: traffic prioritization o  Useful for applications with real-time requirements (eg: SIP)

•  Performs Deep Packet Inspection o  blocks known

–  attacks (exploit signature) ~ 80% –  viruses (signature too)

o  force specific protocol behavior –  eg: limiting the HTTP header to x bytes

o  blocks specific content –  eg: sending PDF files via gmail

Bill Cheswick, The Design of a Secure Internet Gateway, USENIX 1990

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6.1.6. Firewall policy

•  Set of rules

•  Example: •  Block all outgoing FTP traffic except from host ! to

host ! •  Allow only a subset of commands of the SIP protocol

•  Least privilege principle: •  The last evaluated rule has to be

o  “Deny All traffic from any network to any network”

6.1.7. Additional cool stuff

•  Policy depending of the identity of authenticated users: •  Role-Based Access Control

•  Could also have additional functions: •  Proxy •  Failover, Load-Balancing

Firewall - interlude

•  Firewalls and Internet security: repelling the wily hacker, William R. Cheswick, Steven M. Bellovin, Aviel D. Rubin

IV.6.2.1. Proxy

•  Acts as an intermediary for requests from clients to another service.

•  Types •  Forward

•  Open

•  Reverse

•  Applications o  Squid o  Microsoft Forefront Threat Management Gateway (ISA server)

!"#$%"$#&

!"#$%"$#&!"#$%"$#&

!"#$%"$#&

Internal network

Internal server (eg: webserver)

Internal network

IV.6.2.2. Proxy - features

•  Policy: •  Filtering at the application level

o  Similar to Deep-Packet Inspection –  eg: HTTP URL filtering –  DNS: blacklist

•  Caching o  Accelerating some requests o  (eg: Forward proxy loading static content from google.fr from its

cache rather than fetching it again from the Internet)

•  Logging o  Each corporation providing an internet access has to log requests

(liability issues)

•  the policy could be dependent of the authenticated user/comp.

IV.6.2.3. Proxy - SOCKS

•  SOCKet Security, RFC1928, default TCP port 1080 (server) •  The application has to "understand" a SOCKS dialog •  Eg: forward proxy in a corporation ; HTTP GET /

!"#$%"$#&

Internal network

Proxy Client FW

Identity provider

allow HTTP, DNS from proxy to

Internet

!9&2+1$"#M5$%T$%&

GV;WG&

:;9&!9&2+1$"#M0%-XR&

:;9&!9&/5-J%2$&Y&0%-XR7&

:;9&!9&/5-J%2$&Y&0%-XRHZ,7&

IV. 6.3. Services Oriented Architecture

•  Web-Service •  WS-Security •  WS-Federation

6.3.1. Service Oriented Architecture

•  Provides: •  UDDI: Service location •  WSDL: Service description •  SOAP: Remote Procedure Call

•  Interesting: •  Interoperability •  Low-coupling

•  Web-Services and Firewalls: o  Generally TCP 80 or TCP 443 for the

transport. o  "classic DPI" is not enough, since the

"real applications" function at a higher level than HTTP!

U::9&H&O9;&

6.3.2. WS-Security

•  A way of ensuring integrity and confidentiality properties on SOAP messages.

o  Author: OASIS (Microsoft, IBM, !)

•  Credentials: transport of security tokens •  SAML Security Assertion Markup Language

o  Authentication o  Authorization o  .. between "security domains" (eg: Active Directory domains)

•  Kerberos •  X.509

•  Integrity: XML signature •  Encryption: XML encryption

6.3.3. WS-Federation & SAML: identity federation

•  An user authenticates through his Identity Provider (eg: corp A) and gets access to applications published by a Service Provider (eg: corp B) ~ Web-Browser SSO

•  Some definitions (see ADFS 1.0 example next slide) •  Identity Provider (eg: LDAP, SQL database!) •  Claims (FR: revendication)

o  Eg: User.Age >=18

•  Token (FR: jeton) •  Service Provider: provides the application

http://blogs.sun.com/hubertsblog/entry/deep_dive_on_saml_2

6.3.4. Active Directory Federation Services 1.0

o  Example in Business2Businness Web-Browser Single-Sign-On

Active Directory Federation Services 2.0 (2010), Philippe BERAUD , Microsoft

Web Application

Corporation A (Authentication)

Client C

K6L>% K6LM#<L3$,N(%>%

K6LM#<L3$,N(%O%

Corporation R (Ressource)

Identity Provider

DMZ DMZ

A HTTP GET / web app. B 2.1 Authenticate to FS-P B (HTTP 302). I need the claims c1,c2..

2.2 security domain=A

3.1. Plz provide a token from FS-A

3.2 HTTP 302 FS-A User authentication SAML Token Request

FS-A - obtains the attributes from IP - build the claims (c1,c2) - add some information regarding C - signs them = SAML token [C,c1,c2]FS-A

D Intranet Intranet

[C,c1,c2!]FS-A HTTP POST

Token construction: - checks the FS-A token signature - and builds [C,c1,c2]FS-R

I8: HTTP 200 OK, servicing

G7.1 [C,c1,c2..]FS-R

HTTP POST

X.509 cert. exchange FS-R accepts FS-A tokens

IV. 6.4. Public Key Infrastructure

•  Defintion •  Components •  Certification Authority •  Chain of trust •  Certificate issuance •  Revocation •  Example •  PKCS •  Implementation & use cases

Fabien Duchene, Introduction to the Microsoft PKI Active Directory Certificate Services 2008 R2, Sogeti-ESEC

6.4.1. PKI - definition

•  Hardware, software, people, policies and procedures to manage the lifecycle of digital certificates

o  (manage, distribute, use, store and revoke)

•  It uses: asymmetric cryptography o ! and is ONE solution to associate certificates with identity =

hierarchical model o ! other models exist:

–  local trust model (eg: SPKI) –  web of trust (eg: PGP)

X«C» X«A» Z«B»

TISO3960-94/d04

U«V»V«U»

V«W»W«V»

W«X»X«W»X«Z»

Y«Z»Z«Y»Z«X»

V«Y»Y«V»

Figure 4 – CA hierarchy – A hypothetical example4MMSR - Network Security - 2010-2011

6.4.2. PKI - components

W$R5&*"Q&2$%3]2*#$5&&S*"*P$S$"#&&#--+54&*JQ13"P6&

?#$9P5'-#%"7<&25'9,+%'+Q%$#R,5'9,+%Q2)-$2<79,+%",2+-)%%

/;O\4&V;G97&

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8O\5&<_0KHH&&]+$KHH&&+Q*0KHH&

G$2J%1#R&0-+12R&

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*J#<$"32*3-"&

:Q#+9-(%3$,R2Q#$%/$PK&^''G7&

Applications and services .. able to interact with certificates

4MMSR - Network Security - 2010-2011

6.4.3. Certification Authority

•  A trusted party (server), as part of a PKI: •  Verify the identity of a certificate requestor •  Issue certificates to requestors (users, comp)

according to the issuance policy •  Manage certificate revocation*

*revocation: designing a certificate as no more valid, even if its expiration date is future.

Sheldon Cooper

Kim Cameron

Issued certificate

GeekCompany Root CA

6.4.4. PKI – Trust topology

•  ^&42#$'$5425'&&#%J5#&S-Q$+K&– 85$%5H2-S0J#$%5&#%J5#&#<$&O--#&;^&– :%*"513T$&#%J5#&%$+*3-"&3++&#<$&+$*Z5&

I trust that Root CA

! thus I also trust these CA (issued cert. by the Root CA)

! thus I also trust the identity of that

user/comp (issued cert..)

6.4.4 Certificate insuance

•  A Root CA self-signs its certificate •  The most common model: the requester generates the

KeyPair o  Certificate template: set of parameters (key length, authentication

requirements (1/2/3 factor(s)), permissions!

Authenticated Certificate request (public key, validity, certificate template!) C%

B%KeyPair generation (according to the chosen certificate template parameters)

H% Authentication A%

Certificate Templates fetching

Certificate F%

Verifications (template parameters)

Certificate issuance (see next slide)

Identity Provider

Certification Authority

Certificate Template store

Client

6.4.4. Chain of trust & certificate issuance

•  Trust hierarchy: trusting the Root CA •  Signature: each CA signs all issued certificates

•  ! including the child PKI ones!

6.4.4. Chain of trust - signature

;+$*%&#$X#&2$%3]2*#$&1"Z-%S*3-"&

Thumbprint computation

Thumbprint signed with the issuing CA private key

* hash: function that takes a block of data and returns a fixed size bit string. (eg: MD5, SHA-1, SHA-512!)

Cert. Signature field

How could the “chain of trust” be broken?

•  For any certificate in that chain:

•  Validity time: certificate expired? •  Subject name: the certificate information is different to

what the application expects? (eg: loading an https website by its IP, instead of FQDN)

•  Revocation: has that certificate been revoked at the CDP?

•  ! and of course if the Root CA of that chain is not trusted!

Technical overview of the Microsoft PKI ADCS 2008 R2 48

•  CRL (Certificate Revocation List) •  List of revocated certificates hashes periodically fetched

•  OCSP (Online Certificate Status Protocol) •  Real-Time web request

Certificate hash

!  The certificate is not trusted

"  The certificate is trusted

no Periodical CRL download (HTTP, SMB, LDAP!)

6.4.5. PKI - Revocation

Certificate hash

!  The certificate is not trusted

"  The certificate is trusted

Is the certificate revoked?

OCSP Request

OCSP signed Reply

Is the hash present in the signed CRL? (by the issuing CA)

PKI – certificate verification example •  Consider the following scenario:

Should I trust the customer CA

certificate, knowing I obtained the Root CA

cert from the AIA?

0. Get the AIA information periodically (URL, download the Root CA public key)

3. Is the Root CA cert. revoked or expired? (CRL, OCSP) Is it the right computer (DNS FQDN)?

1. The Customer CA is presenting us its certificate (!and the related chain of

trust)

2. Do I trust the Root CA certificate? (“Trusted Root

Certification Authorities”?)

4. Check the Ext. Pol. CA certificate signature (parent CA)

5. 6. 7. 8. !

6.4.7. PKI - PKCS

•  Public-Key Cryptography Standards •  Based on Diffie & Hellmann research (1976)

asymetric crypto •  OS neutral •  Used in many standards relying on asymetric crypto

•  PKCS #1: RSA Encryption Standard •  PKCS #3: Diffie-Hellman Key-

Agreement Standard •  PKCS #5: Password-Based

Cryptography Standard •  PKCS #6: Extended-Certificate Syntax

Standard •  PKCS #7: Cryptographic Message

Syntax Standard •  PKCS #8: Private-Key Information

Syntax Standard

•  PKCS #9: Selected Attribute Types •  PKCS #10: Certification Request

Syntax Standard •  PKCS #11: Cryptographic Token

Interface Standard •  PKCS #12: Personal Information

Exchange Syntax Standard •  PKCS #13: Elliptic Curve

Cryptography Standard •  PKCS #15: Cryptographic Token

Information Format Standard

6.4.8. Some implementations & use cases

•  Web-Security •  SSL: website authentication and data encryption •  Email signature and encryption

•  Corporate security •  2 factors authentication

•  Application/Data integrity •  Java Applets •  Apple iOS applications •  Microsoft Windows updates •  Antimalware signatures

IV.6. Internet - summary

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a '-&#<$R&0$%Z-%S&S*5dJ$%*Q1"Pb&a eP&c^:&1"&!9T@&

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a ̂ 5RS$#%12&2%R0#-P%*0<R&a OG^&

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iv. network security - ensimagensiwiki.ensimag.fr/images/5/5e/network_security_-_4...27 4mmsr -...

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