Redes Inalámbricas – Tema 5. Seguridad · Redes Inalámbricas – Tema 5. Seguridad La...

Redes Inalámbricas – Tema 5. SeguridadRedes Inalámbricas – Tema 5. Seguridad

�La tecnología 802.11: WEP y el estándar 802.11i

�Seguridad en MANET

REDES INALÁMBRICAS Máster de Ingeniería de Computadores 2008/2009

MIC

2008/2

009 Wireless LAN Security Issues

Issue

� Wireless sniffer can view all WLAN data packets

� Anyone in AP coverage area can get on WLAN

802.11 WEP Solution

� Encrypt all data transmitted between client and AP

� Without encryption key, user cannot transmit or receive data

WEP y IEEE802.11iR

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Wireless LAN (WLAN)

Wired LAN

Goal: Make WLAN security equivalent to that of wired LANs (Wired Equivalent Privacy)

client access point (AP)

MIC

2008/2

009 WEP – Protection for 802.11b

�Wired Equivalent Privacy� No worse than what you get with wire-based systems.

� Criteria:� “Reasonably strong”

� Self-synchronizing – stations often go in and out of coverage

� Computationally efficient – in HW or SW since low MIPS CPUs might be used

� Exportable – US export codes (relaxed in Jan 2000 / “Wassenaar Arrangement”)

Optional – not required to used it

WEP y IEEE802.11iR

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� Optional – not required to used it

� Objectives:� confidentiality

� integrity

� authentication

MIC

2008/2

009 WEP – How It Works

� Secret key (40 bits or 104 bits)� can use up to 4 different keys

� Initialization vector (24 bits, by IEEE std.)� total of 64 or 128 bits “of protection.”

� RC4-based pseudo random number generator (PRNG)

� Integrity Check Value (ICV): CRC 32

WEP y IEEE802.11iR

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IV(4 bytes)

Data (PDU)(≥ 1 byte)

Init Vector(3 bytes)

1 byte

Pad6 bits

Key ID2 bits

Frame headerICV

(4 bytes)FCS

MIC

2008/2

009 WEP Encryption Process

1) Compute ICV using CRC-32 over plaintext msg.

2) Concatenate ICV to plaintext message.

3) Choose random IV and concat it to secret key and input it to RC4 to produce pseudo random key sequence.

4) Encrypt plaintext + ICV by doing bitwise XOR with key sequence to produce ciphertext.

5) Put IV in front of cipertext.

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5) Put IV in front of cipertext.

InitializationVector (IV)

Secret Key

Plaintext

Integrity Algorithm

Seed WEP PRNG

KeySequence

Integrity Check Value (ICV)

IV

CiphertextMessage

MIC

2008/2

009 WEP Decryption Process

1) IV of message used to generate key sequence, k.

2) Ciphertext XOR k � original plaintext + ICV.

3) Verify by computing integrity check on plaintext (ICV’) and comparing to recovered ICV.

4) If ICV ≠ ICV’ then message is in error; send error to MAC management and back to sending station.

WEP y IEEE802.11iR

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IV

Ciphertext

Secret Key

Message

WEP PRNG

Seed

KeySequence

Integrity Algorithm

Plaintext

ICV’

ICV

ICV’ - ICV

MIC

2008/2

009 WEP Station Authentication

� Wireless Station (WS) sends Authentication Request to Access Point (AP).

� AP sends (random) challenge text T.

� WS sends challenge response (encrypted T).

� AP sends ACK/NACK.

WS APAuth. Req.

Challenge Text

Challenge Response

WEP y IEEE802.11iR

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Challenge Response

Ack

Client

AP

Access Point

Authentication Request

Challenge

ENC SharedKey {Challenge}

Success/Failure

Shared WEP Key

MIC

2008/2

009 WEP Weaknesses

� Forgery Attack� Packet headers are unprotected, can fake src and dest addresses.

� AP will then decrypt data to send to other destinations.

� Can fake CRC-32 by flipping bits.

� Replay � Can eavesdrop and record a session and play it back later.

� Collision (24 bit IV; how/when does it change?)� Sequential: roll-over in < ½ day on a busy net

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� Sequential: roll-over in < ½ day on a busy net

� Random: After 5000 packets, > 50% of reuse.

�Weak Key� If ciphertext and plaintext are known, attacker can determine key.

� Certain RC4 weak keys reveal too many bits. Can then determine RC4 base key.

�Well known attack described in Fluhrer/Mantin/Shamir paper� “Weaknesses in the Key Scheduling Algorithm of RC4”, Scott Fluhrer, Itsik Mantin,

and Adi Shamir� using AirSnort: http://airsnort.shmoo.com/� Also: WEPCrack

�http://wepcrack.sourceforge.net/

MIC

2008/2

009 Ways to Improve Security with WEP

� Use WEP(!)

� Change wireless network name from default

� any, 101, tsunami

� Turn on closed group feature, if available in AP

� Turns off beacons, so you must know name of the wireless network

� MAC access control table in AP

� War Driving in New Orleans (back in December 2001)

� Equipment

� Laptop, wireless card, software

� GPS, booster antenna (optional)

� Results

� 64 Wireless LAN’s

� Only 8 had WEP Enabled (12%)

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� MAC access control table in AP

� Use Media Access Control address of wireless LAN cards to control access

� Use Radius support if available in AP

� Define user profiles based on user name and password

� 62 AP’s & 2 Peer to Peer Networks

� 25 Default (out of the box) Settings (39%)

� 29 Used The Company Name For ESSID (45%)

MIC

2008/2

009 War Driving

� Locating wireless access points while in motion� http://www.wardrive.net/

� Adversarial Tools� Laptop with wireless adapter

� External omni-directional antenna

� Net Stumbler or variants http://www.netstumbler.com/

� GPS With GPS Support

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Send constant probe requests

MIC

2008/2

009

War Driving in New Orleans (back in December 2001)

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MIC

2008/2

009 Quick and dirty 802.11 Security Methods

� SSID Closed mode

� MAC layer security

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MIC

2008/2

009

Quick and dirty Security Methods: Closed Mode of Operation

� Hide SSID � All devices in a WLAN have to have same SSID to communicate

� SSID is not released� Beacon messages are removed

� Client has to know exact SSID to connect

�Make active scanning, send probe request

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MIC

2008/2

009 Attacking to 802.11 Closed Mode

Client Connection

Disassociate

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Impersonate AP

Client sends Probe Request which includes SSID in clear

Capture Probe Request Packets for SSID information

ClientAP

MIC

2008/2

009 Man-in-the-middle Attack

Wired NetworkAP

ApplicationServer

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Wired Network

Client

AP

Access Point

Impersonate AP to the client

Impersonate Client to the AP

MIC

2008/2

009 Quick and dirty 802.11 Security Methods

� SSID Closed mode

� MAC layer security

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MIC

2008/2

009 Quick and dirty security Methods: MAC Layer Security

� Based on MAC addresses

� MAC filters � Allow associate of a MAC

� Deny associate of a MAC

Wired Network

?

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MAC: 00:05:30:BB:CC:EE

MAC: 00:05:30:AA:AA:AA

?

MIC

2008/2

009 Bypass MAC Filters: MAC Spoofing

Wired Network

Legitimate Client

AP

Access Point Application Server

Association Request

802.11

1 Authentication RespondAuthentication Request

Probe RespondProbe Request

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Association Request

Association Response

Access to NetworkDisassociate

Set MAC address of Legitimate Client by using SMAC or variants 2

Association Request

Association Response

Access to Network

3

45

Monitor

MIC

2008/2

009 Rouge AP

� Install fake AP and web server software

� Convince wireless client to:� Disassociate from legitimate AP

� Associate to fake AP

� Bring similar web application to user to collect passwords

� Adversarial tools:� Any web server running on Unix or MS environments

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� Any web server running on Unix or MS environments

� Fake AP (http://www.blackalchemy.to/project/fakeap/)

Run fake • AP software• Web Server

Wired NetworkAP

Application Server:i.e. Web Server

Reconnect to louder AP

MIC

2008/2

009 IEEE 802.11i: Introducción

� Las redes inalámbricas 802.11 siguen teniendo la fama de inseguras

� Desde el año 2004 se cuenta con el estándar 802.11i, que proporciona una alta seguridad a este tipo de redes� no hay descrito ningún ataque efectivo sobre WPA2 en modo infraestructura

(correctamente configurado)

�WEP dejó de ser una opción a partir del año 2001� ¡pero seguimos burlándonos de él!

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� ya no forma parte del estándar 802.11 (su uso está desaprobado por el añadido 802.11i

� La tecnología actual permite redes Wi-Fi seguras

MIC

2008/2

009 Cronología de la seguridad en 802.11

19971997 19991999 20012001 20032003 20042004

802.11

802.11a

802.11b 802.11g 802.11i

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19971997 19991999 20012001 20032003 20042004

Wi-Fi WPA WPA2

WEP

MIC

2008/2

009 ¿En qué falló WEP?

� utiliza una única clave secreta para todo: autenticación, confidencialidad

� y se usa en todos los dispositivos y durante todo el tiempo

� la gestión de las claves es manual

� la autenticación es sólo para el dispositivo cliente� no se autentica al usuario, ni se autentica la red

� el IV es demasiado pequeño y la forma de usarlo debilita el protocolo

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� el IV es demasiado pequeño y la forma de usarlo debilita el protocolo

� la integridad no funciona (CRC no es un buen código)� y no incluye las direcciones fuente y destino

MIC

2008/2

009 ¿Qué podemos hacer?

� No intentar resolverlo todo de una

� Buscar los protocolos adecuados para cada funcionalidad

� Permitir la gestión automática de las claves de cifrado

� Cambiar frecuentemente las claves, obteniéndolas automáticamente

� Autenticar al usuario, no al dispositivo

� Autenticar a la red (también hay redes ‘malas’)

� Utilizar protocolos robustos de autenticación, integridad y

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� Utilizar protocolos robustos de autenticación, integridad y confidencialidad

MIC

2008/2

009 Primera aproximación: 802.1X

� Control de acceso basado en el puerto de red:

� una vez autenticada y asociada una estación, no se le da acceso a la red hasta que no se autentique correctamente el usuario

� Componentes: suplicante, autenticadory servidor de autenticación

� Utiliza EAP como marco de autenticación

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� EAP permite el uso de distintos protocolosde autenticación: MD5, MS-CHAPv2, …

� La utilización de un método criptográfico en la autenticación permite generar claves secretas

� también se pueden distribuir de manera segura

MIC

2008/2

009 Métodos EAP (1)

� Los métodos EAP en redes Wi-Fi han de cumplir:� protección de las credenciales de usuario

� autenticación mutua usuario �� red

� derivación de claves

� Solución: emplear un túnel TLS� el servidor se autentica con certificado digital

� las credenciales viajan protegidas

TLS genera una clave maestra

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� TLS genera una clave maestra

� ¿Qué servidor autentica? RADIUS� trabaja con distintas Bases de Datos de usuario

� permite la escalabilidad mediante una jerarquía de servidores (en árbol)

MIC

2008/2

009 Métodos EAP (2)

� Los más habituales en Wi-Fi:� EAP-TLS

se utilizan certificados digitales en ambos extremos

� EAP-TTLS (Tunneled TLS)en una primera fase se establece un túnel TLS a partir del certificado digital del servidoren la segunda fase se utiliza cualquier otro método de autenticación (protegido por el túnel). Ej.: PAP, MD5, …

� EAP-PEAP (Protected EAP)

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� EAP-PEAP (Protected EAP)equivalente a TTLS, pero sólo emplea métodos EAP para la segunda fase: TLS, MS-CHAP-V2, …

� Si se emplean dos fases:� identidad anónima en la autenticación externa (dominio)

� identidad real en la autenticación interna

MIC

2008/2

009 El servicio RADIUS

� Permite autenticar a los usuarios que establecen conexiones remotas u 802.1X

� Es capaz de trabajar con distintos repositorios de cuentas de usuario� el Directorio Activo de Windows, LDAP, ficheros, …

� Si el usuario no pertenece a su dominio lanza la petición a su ‘padre’ en la jerarquía RADIUS� en los métodos que utilizan dos fases se emplea la identidad externa para redirigir

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� en los métodos que utilizan dos fases se emplea la identidad externa para redirigir la petición

� Los canales cifrados (túneles TLS) se establecen entre el suplicante y el RADIUS final que atiende la petición

MIC

2008/2

009 Jerarquía RADIUS

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2008/2

009 Primera solución: WPA

� Mientras en el IEEE se trabaja en el nuevo estándar 802.11i, las debilidades de WEP exigen protocolos de cifrado en niveles superiores a la capa de enlace

� La industria es reacia a adoptar las redes 802.11

� El consorcio Wi-Fi Alliance decide sacar el estándar comercial WPA (Wi-Fi Protected Access)

� Se basa en un borrador del estándar 802.11i y es un subconjunto del

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� Se basa en un borrador del estándar 802.11i y es un subconjunto del mismo� compatible hacia delante

� Soluciona todos los problemas que plantea WEP con medidas válidas a medio plazo

MIC

2008/2

009 La confidencialidad en WPA: TKIP

� TKIP (Temporal Key Integrity Protocol) es el protocolo de cifrado diseñado para sustituir a WEP reutilizando el hardware existente

� Forma parte del estándar 802.11i� aunque se considera un protocolo ‘a desaprobar’

� Entre sus características:� utiliza claves maestras de las que se derivan las claves

� el IV se incrementa considerablemente (de 24 a 48 bits)

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� el IV se incrementa considerablemente (de 24 a 48 bits)

� cada trama tiene su propia clave RC4

� impide las retransmisiones de tramas antiguas

� comprueba la integridad con el algoritmo Michael

�no ofrece la máxima seguridad, pero incorpora contramedidas ante los ataques (desconexión 60 s y generación de claves)

MIC

2008/2

009 ¿Cómo se configura WPA?

� Autenticación 802.11 abierta

� Autenticación 802.1X (en modo infraestructura)

� Métodos EAP con túnel TLS� identidad externa anónima, si es posible

� Restricción de los servidores RADIUS aceptados

� Cifrado: TKIP

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� ¿Y si estamos en un entorno SOHO?� no hay servidores RADIUS

� no podemos autenticar al usuario como hasta ahora

� no podemos generar la clave maestra

� � utilizamos una clave pre-compartida entre todos ¡!

MIC

2008/2

009 La solución definitiva: 802.11i = WPA2

� El protocolo CCMP ofrece el cifrado (mediante AES) y la protección de integridad� se considera el algoritmo de cifrado más seguro hoy en día (no se ha ideado

ningún ataque contra el mismo)

� necesita soporte hardware para no penalizar

� aunque se han incorporado mejoras en el diseño para hacerlo más eficiente

� Se establece el concepto RSN: Robust Security Networks� aquellas en las que todas las asociaciones entre dos dispositivos son de tipo RSNA

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� aquellas en las que todas las asociaciones entre dos dispositivos son de tipo RSNA� intercambio de claves con un 4-Way Handshake

MIC

2008/2

009 Asociaciones de tipo RSNA

� Una vez que el usuario se ha autenticado ante el RADIUS, ambos han generado una clave maestra

� El RADIUS le proporciona esta clave al AP

� El punto de acceso y el cliente realizan un diálogo (con 4 mensajes) en el que:� comprueban que el otro tiene en su poder la clave maestra

� sincronizan la instalación de claves temporales

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� sincronizan la instalación de claves temporales

� confirman la selección de los protocolos criptográficos

� Las claves temporales son de dos tipos:� para el tráfico unicast (estación �� AP)

� para el tráfico multicast y broadcast (AP � estaciones)

MIC

2008/2

009 ¿Cómo se configura WPA2?

� Autenticación 802.11 abierta

� Autenticación 802.1X (en modo infraestructura)

� Métodos EAP con túnel TLS� identidad externa anónima, si es posible

� Restricción de los servidores RADIUS aceptados

� Cifrado: AES

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� ¿Y si estamos en un entorno SOHO?� utilizamos una clave pre-compartida entre todos

� esta clave sirve de autenticación

� esta es la clave maestra a partir de la que generar el resto

LA PALABRA DE PASO HA DE TENER MÁS DE 20 CARACTERES

MIC

2008/2

009 WPA y WPA2

�WPA puede ejecutarse con todo el hardware que soportase WEP (sólo necesita una actualización de firmware)

�WPA2 necesita hardware reciente (2004 �)

�WPA acabará siendo comprometido a medio plazo y sólo se recomienda como transición a WPA2

� Algunos AP permiten emplear un modo mixto que acepta tanto

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� Algunos AP permiten emplear un modo mixto que acepta tanto clientes WPA como clientes WPA2 en la misma celda� hay una pequeña degradación en las claves de grupo

(este modo nos ha dado problemas con algunas PDA)

MIC

2008/2

009 Pre-autenticación 802.1X

� El proceso de establecer la asociación y generar las claves es costoso y puede afectar a la movilidad

� La pre-autenticación consiste en establecer el contexto de seguridad con un AP mientras se está asociado a otro

� El tráfico entre la estación y el nuevo AP viaja por la red cableada

� Cuando, finalmente, se produce el roaming, el cliente indica que ya está hecha la asociación inicial

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está hecha la asociación inicial

� Sólo disponible en WPA2 (excluido en WPA)

MIC

2008/2

009 Soporte 802.11i en los S. Operativos

�Windows Mobile� ¡Cada PDA es un mundo!

� Incluye el suplicante 802.1X

� Soporta sólo WPA (cifrado TKIP)

� métodos EAP: EAP-TLS y EAP-PEAP/MS-CHAP-V2

�Windows XP SP2� Incluye el suplicante 802.1X

Soporta WPA (de fábrica). Se puede aplicar la actualización a WPA2 (si la tarjeta lo

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� Soporta WPA (de fábrica). Se puede aplicar la actualización a WPA2 (si la tarjeta lo soporta)

�esta actualización no se aplica a través de Windows Update


� permite restringir los servidores RADIUS aceptados

� almacena en caché las credenciales del usuario ¡siempre!

MIC

2008/2


�Windows Vista� Incluye el suplicante 802.1X

� Soporta WPA y WPA2


� incorpora una API (EAPHost) que permite desarrollar nuevos suplicantes y nuevos métodos EAP


� permite elegir si se almacenan o no, en caché, las credenciales del usuario

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� Permite definir perfiles de conexión para configurar las redes inalámbricas sin la intervención del usuario

� incluso con opciones que no podrá modificar

� Informa de la seguridad de las redes disponibles

MIC

2008/2


� Linux� Dependiendo de la distribución puede incluir o no el suplicante 802.1X

� Se recomienda utilizar wpa-supplicant y Network Manager para la configuración

� Soporta WPA y WPA2

� admite la mayoría de métodos EAP: EAP-TLS, EAP-TTLS/PAP, EAP-PEAP/MS-CHAP-V2, …



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� la configuración puede ser a través de ficheros o mediante la interfaz gráfica

MIC

2008/2

009 eduroam

� Es una iniciativa a nivel internacional que permite la movilidad de sus miembros de manera ‘transparente’� con la misma configuración de la red inalámbrica se puede conectar un usuario en

cualquier institución adherida a eduroam

� la autenticación del usuario la hace siempre la institución de origen (con seguridad en el tránsito de credenciales)

� es sencillo detectar si tenemos soporte para eduroam: el SSID es eduroam

� Más información:

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� Más información:� http://www.eduroam.es, http://eduroam.upv.es

� Atención: el cifrado puede ser distinto en cada red

MIC

2008/2

009 eduroam en Europa

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MIC

2008/2

009 La red inalámbrica en la UPV

http://wifi.upv.es

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�Seguridad en MANET


MIC

2008/2

009 Routing security vulnerabilities

�Wireless medium is easy to snoop on

� Due to ad hoc connectivity and mobility, it is hard to guarantee access to any particular node (for instance, to obtain a secret key)

� Easier for trouble-makers to insert themselves into a mobile ad hoc network (as compared to a wired network)

� Open medium

� Dynamic topology

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� Dynamic topology

� Distributed cooperation(absence of central authorities)

� Constrained capability(energy)

MIC

2008/2

009 Securing Ad Hoc Networks

� Definition of “Attack” RFC 2828 — Internet Security Glossary :� “ An assault on system security that derives from an intelligent threat, i.e., an

intelligent act that is a deliberate attempt (especially in the sense of a method or technique) to evade security services and violate the security policy of the system.”

� Goals� Availability: ensure survivability of the network despite denial of service attacks.

The DoS can be targeted at any layer

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The DoS can be targeted at any layer

� Confidentiality: ensures that certain information is not disclosed to unauthorized entities. Eg Routing information information should not be leaked out because it can help to identify and locate the targets

� Integrity: guarantee that a message being transferred is never corrupted.

� Authentication: enables a node to ensure the identity of the nodes communicating.

� Non-Repudiation: ensures that the origin of the message cannot deny having sent the message

MIC

2008/2

009 Routing attacks

Classification:

� External attack vs. Internal attack� External: Intruder nodes can pose to be a part of the network injecting erroneous

routes, replaying old information or introduce excessive traffic to partition the network

� Internal: The nodes themselves could be compromised. Detection of such nodes is difficult since compromised nodes can generate valid signatures.

� Passive attack vs. Active attack

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� Passive attack vs. Active attack� Passive attack: “Attempts to learn or make use of information from the system but

does not affect system resources” (RFC 2828)

� Active attack: “Attempts to alter system resources or affect their operation” (RFC 2828)

MIC

2008/2

009 Normal Flow

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Information source

Information destination

MIC

2008/2

009 Passive Attacks

Sniffer

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Passive attacks

Interception (confidentiality)

Release of message contents Traffic analysis

MIC

2008/2

009 Sniffers

� All machines on a network can “hear” ongoing traffic

� A machine will respond only to data addressed specifically to it

� Network interface: “promiscuous mode” – able to capture all framestransmitted on the local area network segment

� Risks of Sniffers:� Serious security threat

� Capture confidential information

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� Capture confidential information

�Authentication information

�Private data

� Capture network traffic information

MIC

2008/2

009

Information source


InterceptionR

ED

ES

INA

LÁ

MB

RIC

AS Unauthorized party gains access to the asset –

ConfidentialityExample: wiretapping, unauthorized copying of files

MIC

2008/2

009 Passive attacks

� Release of message contents� Intruder is able to interpret and extract information being transmitted

� Highest risk: authentication information

�Can be used to compromise additional system resources

� Traffic analysis� Intruder is not able to interpret and extract the transmitted information

RE

DE

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AL

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ICA

S

� Intruder is not able to interpret and extract the transmitted information� Intruder is able to derive (infer) information from the traffic characteristics

MIC

2008/2

009 Protection against passive attacks

� Shield confidential data from sniffers: cryptography

� Disturb traffic pattern:� Traffic padding

� Onion routing

� Modern switch technology: network traffic is directed to the destination interfaces

� Detect and eliminate sniffers

RE

DE

S IN

AL

ÁM

BR

ICA

S

MIC

2008/2

009 Active attacks

Active attacks

Interruption Modification Fabrication(availability) (integrity) (integrity)

RE

DE

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AL

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BR

ICA

S

(availability) (integrity) (integrity)

MIC

2008/2

009

Information source


InterruptionR

ED

ES

INA

LÁ

MB

RIC

AS

Asset is destroyed or becomes unavailable - AvailabilityExample: destruction of hardware, cutting communicationline, disabling file management system, etc.

MIC

2008/2

009 Denial of service attack

� Adversary floods irrelevant data

� Consume network bandwidth

� Consume resource of a particular node

� E-mail bombing attack: floods victim’s mail with large bogus messages� Popular

� Free tools available

� Smurf attack:

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� Smurf attack: � Attacker multicast or broadcast an Internet Control Message Protocol (ICMP) with

spoofed IP address of the victim system

� Each receiving system sends a respond to the victim

� Victim’s system is flooded

MIC

2008/2

009 TCP SYN flooding

� Server: limited number of allowed half-open connections

� Backlog queue: � Existing half-open connections

� Full: no new connections can be established

� Time-out, reset

� Attack:� Attacker: send SYN requests to server with IP source that unable to response to

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� Attacker: send SYN requests to server with IP source that unable to response to SYN-ACK

� Server’s backlog queue filled

� No new connections can be established

� Keep sending SYN requests

�Does not affect � Existing or open incoming connections

� Outgoing connections

MIC

2008/2

009 Protection against DoS, DDoS

� Hard to provide full protection

� Some of the attacks can be prevented� Filter out incoming traffic with local IP address as source

� Avoid established state until confirmation of client’s identity

� Internet trace back: determine the source of an attack

RE

DE

S IN

AL

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BR

ICA

S

MIC

2008/2

009

Information source


ModificationR

ED

ES

INA

LÁ

MB

RIC

AS

Unauthorized party tampers with the asset – IntegrityExample: changing values of data, altering programs, modify content of a message, etc.

MIC

2008/2

009 Attacks using modification

� Attacks using modification

� Idea:� Malicious node announces better routes than the other nodes in order to be

inserted in the ad-hoc network

� How ?� Redirection by changing the route sequence number

� Redirection with modified hop count

RE

DE

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AL

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BR

ICA

S

� Denial Of Service (DOS) attacks

� Modify the protocol fields of control messages

� Compromise the integrity of routing computation

� Cause network traffic to be dropped, redirected to a different destination or take a longer route

MIC

2008/2


Redirection with modified hop count:- The node C announces to B a path with a metric value of one - The intruder announces to B a path with a metric value of one too- B decides which path is the best by looking into the hop count value of each

route

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DE

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Node A Node B Node D

Node C

Intruder

Metric 1 and 3 hops

Metric 1 and 1 hop

MIC

2008/2


� Denial Of Service (DOS) attacks with modified source routes: � A malicious node is inserted in the network

� The malicious node changes packet headers it receives

� The packets will not reach the destination:

� The transmission is aborted

Intruder I decapsulates

packets, change the

Node A sends packets

with header: (route cache

Node C has no direct

route with E, also the

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DE

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AL

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ICA

S Node A Node B Node DNode CIntruder I

packets, change the

header:

A-B-I-C-E

with header: (route cache

to reach node E)

A-B-I-C-D-E

route with E, also the

packets are dropped

Node E

MIC

2008/2

009

Information source


FabricationR

ED

ES

INA

LÁ

MB

RIC

AS

Unauthorized party insets counterfeit object into the system – AuthenticityExample: insertion of offending messages, addition of records to a file, etc.

MIC

2008/2

009 Attacks using fabrication

� Attacks using fabrication� Idea:

�Generates traffic to disturb the good operation of an ad-hoc network

� How ?

�Falsifying route error messages

� Corrupting routing state

RE

DE

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� Routing table overflow attack

� Replay attack

� Black hole attack

MIC

2008/2


� Falsifying route error messages: � When a node moves, the closest node sends “error” message to the others

� A malicious node can usurp the identity of another node (e.g. By using spoofing) and sends error messages to the others

� The other nodes update their routing tables with these bad information

� The “victim” node is isolated

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MIC

2008/2


� Corrupting routing state: � In DSR, routes can be learned from promiscuously received packets

� A node should add the routing information contained in each packet’s header it overhears

� A hacker can easily broadcast a message with a spoofed IP address such as the other nodes add this new route to reach a special node S

� It’s the malicious node which will receive the packets intended to S.

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MIC

2008/2


� Routing table overflow attack: � Available in “pro-active” protocols.

� These protocols try to find routing information before they are needed

� A hacker can send in the network a lot of route to non-existent nodes until overwhelm the protocol

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MIC

2008/2


� Replay attack:� A hacker sends old advertisements to a node

� The node updates its routing table with stale routes

� Black hole attack: � A hacker advertises a zero metric route for all destinations

� All the nodes around it will route packets towards it

RE

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MIC

2008/2

009 Attacks using impersonation

� Attacks using impersonation� Idea :

�Usurpates the identity of another node to perform changes

� How ?

�Spoofing MAC address of other nodes

RE

DE

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MIC

2008/2


� Forming loops by spoofing MAC address: � A malicious node M can listen all the nodes when the others nodes can only listen

their closest neighbors

� Node M first changes its MAC address to the MAC address of the node A

� Node M moves closer to node B than node A is, and stays out of range of node A

� Node M announces node B a shorter path to reach X than the node D gives

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ICA

S

A

B

C

D E X

M

MIC

2008/2


� Forming loops by spoofing MAC address: � Node B changes its path to reach X

� Packets will be sent first to node A

� Node M moves closer to node D than node B is, and stays out of range of node B

� Node M announces node D a shorter path to reach X than the node E gives

RE

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S

A

B

C

D E X

M

MIC

2008/2


� Forming loops by spoofing MAC address: � Node D changes its path to reach X

� Packets will be sent first to node B

� X is now unreachable because of the loop formed

RE

DE

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ICA

S

A

B

C

D E X

M

MIC

2008/2

009 Other Routing attacks

� Attacks for routing:� Wormhole attack (tunneling)

� Invisible node attack

� The Sybil attack

� Rushing attack

� Non-cooperation

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MIC

2008/2

009 Wormhole attack

� Colluding attackers uses “tunnels” between them to forward packets

� Place the attacker in a very powerful position

� The attackers take control of the route by claiming a shorter path

Ntunnel

RE

DE

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S

A

M

B

C

N

D

S

tunnel

MIC

2008/2

009

Invisible node attack

� Attack on DSR

� Malicious does not append its IP address

� M becomes “invisible” on the path

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CMBS D

MIC

2008/2

009 The Sybil attack

� Represents multiple identities

� Disrupt geographic and multi-path routing

B

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DE

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M1

M4

M5M2

M3

MIC

2008/2

009 Rushing attack

� Directed against on-demand routing protocols

� The attacker hurries route request packet to the next node to increase the probability of being included in a route

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MIC

2008/2

009 Non-cooperation

� Node lack of cooperation, not participate in routing or packet forwarding

� Node selfishness, save energy for itself

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�Seguridad en MANET � Algunas soluciones


MIC

2008/2

009 TESLA Overview

� Broadcast authentication protocol used here for authenticating routing messages� Efficient and adds only a single message authentication code (MAC) to a message

� Requires asymmetric primitive to prevent others from forging MAC

� TESLA achieves asymmetry through clock synchronization and delayed key disclosure

RE

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MIC

2008/2

009 TESLA Overview (cont.)

1. Each sender splits the time into intervals

2. It then chooses random initial key (KN)

3. Generates one-way key chain through repeated use of a one-way hash function (generating one key per time interval)

KN-1=H[KN], KN-2=H[KN-1]…

These keys are used in reverse order of generation

4. The sender discloses the keys based on the time intervals

RE

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MIC

2008/2

009 TESLA Overview (cont.)

� Sender attaches MAC to each packet� Computed over the packet’s contents

� Sender determines time interval and uses corresponding value from one-way key chain

� With the packet, the sender also sends the most recent disclosable one-way chain value

� Receiver knows the key disclosing schedule� Checks that the key used to compute the MAC is still secret by determining that

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� Checks that the key used to compute the MAC is still secret by determining that the sender could not have disclosed it yet

� As long as the key is still secret, the receiver buffers the packet

�When the key is disclosed, receiver checks its correctness (through self-authentication) and authenticates the buffered packets

MIC

2008/2

009 Assumptions

� Of the network� Network links are bidirectional

� The network may drop, corrupt, reorder or duplicate packets

� Each node must be able to estimate the end-to-end transmission time to any other node in the network

� Disregard physical attacks and Medium Access Control attacks

� Of the nodes

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� Resources of nodes may vary greatly, so Ariadne assumes constrained nodes

� All nodes have loosely synchronized clocks

MIC

2008/2

009 Security Assumptions

� Three authentication mechanism possibilities:� Pairwise secret keys (requires n(n+1)/2 keys)

� TESLA (shared keys between all source-destination pairs)

� Digital signatures (requires powerful nodes)

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MIC

2008/2

009 Key Setup

� Shared secret keys� Key distribution center

� Bootstrapping from a Public Key Infrastructure

� Pre-loading at initialization

� Initial TESLA keys� Embed at initialization

� Assume PKI and embed Certifications Authority’s public key at each node

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MIC

2008/2

009 Ariadne Overview

� Authenticate routing messages using one of:� Shared secrets between each pair of nodes

�Avoids need for synchronization

� Shared secrets between communicating nodes combined with broadcast authentication

�Requires loose time synchronization

�Allows additional protocol optimizations

� Digital signatures

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MIC

2008/2

009 Ariadne Notation

� A and B are principals (e.g., communicating nodes)

� KAB and KBA are secret MAC keys shared between A and B

� MACKAB(M) is computation of MAC of message M using key KAB

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MIC

2008/2

009 Route Discovery

� Assume sender and receiver share secret (non-TESLA) keys for message authentication

� Target authenticates ROUTE REQUESTS� Initiator includes a MAC computed with end-to-end key

� Target verifies authenticity and freshness of request using shared key

� Data authentication using TESLA keys� Each hop authenticates new information in the REQUEST

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� Each hop authenticates new information in the REQUEST

� Target buffers REPLY until intermediate nodes release TESLA keys

�TESLA security condition is verified at the target

�Target includes a MAC in the REPLY to certify the condition was met

� Attacker can remove a node from node list in a REQUEST

� One-way hash functions verify that no hop was omitted (per-hop hashing)

MIC

2008/2

009 Route Discovery (cont.)

� Assume all nodes know an authentic key of the TESLA one-way key chain of every other node

� Securing ROUTE REQUEST� Target can authenticate the sender (using their additional shared key)

� Initiator can authenticate each path entry using intermediate TESLA keys

� No intermediate node can remove any other node in the REQUEST or REPLY

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MIC

2008/2


� Upon receiving ROUTE REQUEST, a node:� Processes the request only if it is new

� Processes the request only if the time interval is valid (not too far in the future, but not for an already disclosed TESLA key)

� Modifies the request and rebroadcasts it

�Appends its address to the node list, replaces the hash chain with H[A, hash chain], appends MAC of entire REQUEST to MAC list using KAi where i is the index for the time interval specified in the REQUEST

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index for the time interval specified in the REQUEST

MIC

2008/2


�When the target receives the route request:� Checks the validity of the REQUEST (determining that the keys from the time

interval have not been disclosed yet and that hash chain is correct)

� Returns ROUTE REPLY containing eight fields

�ROUTE REPLY, target, initiator, time interval, node list, MAC list

�target MAC: MAC computed over above fields with key shared between target and initiator

�key list: disclosable MAC keys of nodes along the path

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�key list: disclosable MAC keys of nodes along the path

MIC

2008/2


� Node forwarding ROUTE REPLY� Waits until it can disclose TESLA key from specified interval

�Appends that key to the key list

�This waiting does delay the return of the ROUTE REPLY but does not consume extra computational power

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MIC

2008/2


�When initiator receives ROUTE REPLY� Verifies each key in the key list is valid

� Verifies that the target MAC is valid

� Verifies that each MAC in the MAC list is valid using the TESLA keys

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MIC

2008/2

009 Route Maintenance

� Based on DSR� Node forwarding a packet to the next hop returns a ROUTE ERROR to the original

sender

� Prevent unauthorized nodes from sending errors, we require errors to be authenticated by the sender

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MIC

2008/2

009 Route Maintenance

� Errors are propagated just as regular data packets� Intermediate nodes remove routes that use the bad link

� Sending node continues to send data packets along the route until error is validated� Generates additional errors, which are all cleaned up when the error is finally

validated

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MIC

2008/2

009 Anonymous Communication

� Sometimes security requirement may include anonymity

� Availability of an authentic key is not enough to prevent traffic analysis

�We may want to hide the source or the destination of a packet, or simply the amount of traffic between a given pair of nodes

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simply the amount of traffic between a given pair of nodes

MIC

2008/2

009 Traffic Analysis

� Traditional approaches for anonymous communication, for instance, based on MIX nodes or dummy traffic insertion, can be used in wireless ad hoc networks as well

� However, it is possible to develop new approaches considering the broadcast nature of the wireless channel

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MIC

2008/2

009 Mix Nodes

� Mix nodes can reorder packets from different flows, insert dummy packets, or delay packets, to reduce correlation between packets in and packets out

DG

RE

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S

M1 B M2 E

A

M3C

D

F

MIC

2008/2

009 Mix Nodes

� Node A wants to send message M to node G. Node A chooses 2 Mix nodes (in general n mix nodes), say, M1 and M2

DG

RE

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M1 B M2 E

A

M3C

D

F

MIC

2008/2

009 Mix Nodes

� Node A transmits to M1message K1(R1, K2(R2, M)) where Ki() denotes encryption using public key Ki of Mix i, and Ri is a random number

DG

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M1 B M2 E

A

M3C

D

F

MIC

2008/2

009 Mix Nodes

� M1 recovers K2(R2,M) and send to M2

DG

RE

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M1 B M2 E

A

M3C

D

F

MIC

2008/2

009 Mix Nodes

� M2 recovers M and sends to G

DG

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M1 B M2 E

A

M3C

D

F

MIC

2008/2

009 Mix Nodes

� If M is encrypted by a secret key, no one other than G or A can know M

� Since M1 and M2 “mix” traffic, observers cannot determine the

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� Since M1 and M2 “mix” traffic, observers cannot determine the source-destination pair without compromising M1 and M2 both

MIC

2008/2

009

Alternative Mix Nodes

� Suppose A uses M2 and M3 (not M1 and M2)

� Need to take fewer hops

� Choice of mix nodes affects overhead

DG

RE

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M1 B M2 E

A

M3C

D

F

MIC

2008/2

009 Mix Node Selection

� Intelligent selection of mix nodes can reduce overhead

�With mobility, the choice of mix nodes may have to be modified to reduce cost

� However, change of mix selection has the potential for divulging more

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� However, change of mix selection has the potential for divulging more information

Redes Inalámbricas – Tema 5. Seguridad · Redes Inalámbricas – Tema 5. Seguridad La...

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