Redes Inalámbricas – Tema 7. Seguridad

Redes Inalámbricas – Tema 7. Seguridad
La tecnología : WEP y el estándar i Seguridad en MANET

Wireless LAN Security Issues
WEP y IEEE802.11i Wireless LAN Security Issues Issue Wireless sniffer can view all WLAN data packets Anyone in AP coverage area can get on WLAN WEP Solution Encrypt all data transmitted between client and AP Without encryption key, user cannot transmit or receive data Wireless LAN (WLAN) Wired LAN client access point (AP) Goal: Make WLAN security equivalent to that of wired LANs (Wired Equivalent Privacy)

WEP – Protection for 802.11b Wired Equivalent Privacy Criteria:
WEP y IEEE802.11i WEP – Protection for b 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 Cifrado 64 bits  Reduce el ancho en 1 Mbps Cifrado 128 bits  Reduce el ancho entre 1 y 2 Mbps Impacto dependerá del hardware y del número de usuarios Optional – not required to used it Objectives: confidentiality integrity authentication

WEP – How It Works Protocolo de Encriptación WEP
WEP y IEEE802.11i 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 Protocolo de Encriptación WEP IV = 4 bytes; 3 bytes IV; 1 byte KeyID

WEP Encryption Process
WEP y IEEE802.11i WEP Encryption Process Compute ICV using CRC-32 over plaintext msg. Concatenate ICV to plaintext message. Choose random IV and concat it to secret key and input it to RC4 to produce pseudo random key sequence. Encrypt plaintext + ICV by doing bitwise XOR with key sequence to produce ciphertext. Put IV in front of cipertext. Initialization Vector (IV) IV Key Sequence Seed Message Secret Key WEP PRNG Ciphertext Plaintext Integrity Algorithm Integrity Check Value (ICV)

WEP Decryption Process
WEP y IEEE802.11i WEP Decryption Process IV of message used to generate key sequence, k. Ciphertext XOR k  original plaintext + ICV. Verify by computing integrity check on plaintext (ICV’) and comparing to recovered ICV. If ICV  ICV’ then message is in error; send error to MAC management and back to sending station. Secret Key Key Sequence Plaintext WEP PRNG IV Seed Ciphertext Message ICV’ Integrity Algorithm ICV’ - ICV ICV

WEP Station Authentication
WEP y IEEE802.11i 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 AP Auth. Req. Challenge Text Challenge Response Ack Client AP Access Point Authentication Request Challenge ENC SharedKey {Challenge} Success/Failure Shared WEP Key

WEP Weaknesses Forgery Attack Replay
WEP y IEEE802.11i 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 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: Also: WEPCrack

Cronología de RIP WEP Fallos de Seguridad de Wep
Debilidad del algoritmo RC2 IVs demasiado cortos Se permite la reutilización de IV CRC no es criptográficamente seguro Wep no incorpora un método de distribución de claves

Ways to Improve Security with WEP
WEP y IEEE802.11i 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 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 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%) 62 AP’s & 2 Peer to Peer Networks 25 Default (out of the box) Settings (39%) 29 Used The Company Name For ESSID (45%)

Send constant probe requests
War Driving Locating wireless access points while in motion Adversarial Tools Laptop with wireless adapter External omni-directional antenna Net Stumbler or variants GPS With GPS Support Send constant probe requests

War Driving in New Orleans (back in December 2001)
WEP y IEEE802.11i War Driving in New Orleans (back in December 2001)

Descubriendo Clave Wep
1) airodump Herramienta de sniffing para descubrir redes 2) aireplay Herramienta de inyección para incrementar el tráfico. Requiere modo monitor, equivalente al modo promiscuo Con los drivers parcheados permite con una tarjeta, capturar e inyectar tráfico simultaneamente 3) aircrack Crackeador de claves que utiliza los Ivs recogidos

Descubriendo Clave Wep: secuencia de comandos
#airodump ath0 claves-wep 0 Escanea todos los canales y el resultado en un fichero claves-wep Detectamos un punto de acceso con seguridad Wep y una estación asociado al mismo y vemos en que canal está #airodump ath0 claves-wep 1 Ponemos a escanear el canal 1 en concreto #aireplay -3 –b 00:13:10:…. –h 00:0C:ab: …. –x 600 ath0 Procedemos a inyección depaquetes en la red objetivo para obtener nuevos IV. La inyección comenzará cuando se capture una petición ARP en la red objetivo #aircrack –x -0 claves-wep.cap Una vez tengamos suficientes IVs podremos desencriptar la clave

Descubriendo Clave Wep
Otros tipo de ataque Aircrack Deautenticación: Para recuperar SSID ocultos, denegación de servicios o ataques a WPA Autenticación falsa: Sirve para lanzar ataques sin necesidad de un cliente legítimo. Otros: chopchop, CRC, …

Quick and dirty 802.11 Security Methods
SSID Closed mode MAC layer security Service set identifier (SSID)

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

Attacking to 802.11 Closed Mode
Impersonate AP Client Connection Disassociate Client sends Probe Request which includes SSID in clear Capture Probe Request Packets for SSID information Client AP

Man-in-the-middle Attack
Wired Network Client AP Access Point Application Server Impersonate AP to the client Impersonate Client to the AP

Quick and dirty 802.11 Security Methods
SSID Closed mode MAC layer security Service set identifier (SSID)

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

Bypass MAC Filters: MAC Spoofing
Wired Network Legitimate Client AP Access Point Application Server Association Request 802.11 Association Response Access to Network Disassociate Set MAC address of Legitimate Client by using SMAC or variants 2 3 4 5 1 Monitor Authentication Respond Authentication Request Probe Respond Probe Request

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 Fake AP ( Wired Network AP Application Server: i.e. Web Server Reconnect to louder AP Run fake AP software Web Server

IEEE i: Introducción Las redes inalámbricas siguen teniendo la fama de inseguras Desde el año 2004 se cuenta con el estándar i, 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! ya no forma parte del estándar (su uso está desaprobado por el añadido i La tecnología actual permite redes Wi-Fi seguras

Cronología de la seguridad en 802.11
802.11b 1997 1999 2001 2003 2004 Wi-Fi WPA WPA2 Weaknesses in the Key Scheduling Algorithm of RC4 Fluhrer, Mantin, Shamir WEP

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

¿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 confidencialidad

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, autenticador y servidor de autenticación Utiliza EAP como marco de autenticación EAP permite el uso de distintos protocolos de autenticación: MD5, MS-CHAPv2, … La utilización de un método criptográfico en la autenticación permite generar claves secretas también se pueden distribuir de manera segura

IEEE 802.1X y EAP PAE: Port Access Entity
PAE de autenticación y PAE de Servicio Comunicación Suplicante - Autenticador: EAP Si EAP tiene éxito: Suplicante y Servidor de Autenticación tendrán una claves maestra secreta para comunicarse Comunicación Autenticador – Servidor de Autenticación: Radius

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 ¿Qué servidor autentica? RADIUS trabaja con distintas Bases de Datos de usuario permite la escalabilidad mediante una jerarquía de servidores (en árbol)

Métodos EAP (2) Los más habituales en Wi-Fi: Si se emplean dos fases:
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 servidor en la segunda fase se utiliza cualquier otro método de autenticación (protegido por el túnel). Ej.: PAP, MD5, … 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

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

Jerarquía RADIUS

Primera solución: WPA Mientras en el IEEE se trabaja en el nuevo estándar i, las debilidades de WEP (seguridad, autenticación y encriptación) exigen protocolos de cifrado en niveles superiores a la capa de enlace La industria es reacia a adoptar las redes El consorcio Wi-Fi Alliance decide sacar el estándar comercial WPA (Wi-Fi Protected Access) Se basa en un borrador del estándar i y es un subconjunto del mismo compatible hacia delante Soluciona todos los problemas que plantea WEP con medidas válidas a medio plazo Separación de los procesos de: Autenticación  802.1X Integración y privacidad  TKIP

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 i 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) 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)

¿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 ¿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 ¡!

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 La asociación recibe el nombre de RSNA si éstas se producen con intercambio de claves con un 4-Way Handshake AES (Advanced Encription Standard) es a CCMP lo que RC4 es a TKIP TKIP se diseño para acomodar al hardware WEP existente CCMP es un diseño completamente nuevo diseñado por expertos en seguridad y encriptación TSN: Transitional Security Network. Arquitectura i que permite estaciones tanto WEP como RSN

Las 4 fases del protocolo 802.11i
El establecimiento de un contexto seguro i consta de 4 fases

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 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)

¿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 ¿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

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 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)

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 Sólo disponible en WPA2 (excluido en WPA)

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 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!

Windows Vista Incluye el suplicante 802.1X Soporta WPA y WPA2 métodos EAP: EAP-TLS y EAP-PEAP/MS-CHAP-V2 incorpora una API (EAPHost) que permite desarrollar nuevos suplicantes y nuevos métodos EAP permite restringir los servidores RADIUS aceptados permite elegir si se almacenan o no, en caché, las credenciales del usuario 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 MAC WPA2 está soportado tras la actualización 4.2 del software Apple AirPort: los mac con Airport Extreme, la estación base Airport Extreme Base Station y Airport Express.

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, … permite restringir los servidores RADIUS aceptados permite elegir si se almacenan o no, en caché, las credenciales del usuario la configuración puede ser a través de ficheros o mediante la interfaz gráfica Archivo de configuración de wpa_supplicant para WPA2

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: Atención: el cifrado puede ser distinto en cada red

eduroam en Europa

Seguridad 802.11 en la Red Enlaces Web La Red inalámbrica de la UPV:

La tecnología : WEP y el estándar i Seguridad en MANET

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 Distributed cooperation (absence of central authorities) Constrained capability (energy) sårbart

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 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

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 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)

Normal Flow Information source Information destination

Passive Attacks Sniffer Passive attacks Interception (confidentiality)
Release of message contents Traffic analysis

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 frames transmitted on the local area network segment Risks of Sniffers: Serious security threat Capture confidential information Authentication information Private data Capture network traffic information

Interception Information source Information destination
Unauthorized party gains access to the asset – Confidentiality Example: wiretapping, unauthorized copying of files

Passive attacks Release of message contents Traffic analysis
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 Intruder is able to derive (infer) information from the traffic characteristics

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

Active attacks Active attacks Interruption Modification Fabrication
(availability) (integrity) (integrity)

Interruption Information source Information destination
Asset is destroyed or becomes unavailable - Availability Example: destruction of hardware, cutting communication line, disabling file management system, etc.

Denial of service attack
Adversary floods irrelevant data Consume network bandwidth Consume resource of a particular node bombing attack: floods victim’s mail with large bogus messages Popular Free tools available 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

TCP SYN flooding Attack: Does not affect
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 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

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

Modification Information Information source destination
Unauthorized party tampers with the asset – Integrity Example: changing values of data, altering programs, modify content of a message, etc.

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 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

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 Node C Node A Node B Node D Metric 1 and 3 hops Intruder Metric 1 and 1 hop

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 Node A sends packets with header: (route cache to reach node E) A-B-I-C-D-E Intruder I decapsulates packets, change the header: A-B-I-C-E Node C has no direct route with E, also the packets are dropped Node A Node B Node C Node D Intruder I Node E

Fabrication Information source Information destination
Unauthorized party insets counterfeit object into the system – Authenticity Example: insertion of offending messages, addition of records to a file, etc.

Attacks using fabrication
Idea: Generates traffic to disturb the good operation of an ad-hoc network How ? Falsifying route error messages Corrupting routing state Routing table overflow attack Replay attack Black hole attack

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

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.

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

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

Attacks using impersonation
Idea : Usurpates the identity of another node to perform changes How ? Spoofing MAC address of other nodes

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 A C M B D E X

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 A B C D E X M

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 A C M B D E X

Other Routing attacks Attacks for routing: Wormhole attack (tunneling)
Invisible node attack The Sybil attack Rushing attack Non-cooperation

……..…. Wormhole attack N M D C S B A
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 tunnel N ……..…. M D C S B A

S B M C D Attack on DSR Malicious does not append its IP address
Invisible node attack Attack on DSR Malicious does not append its IP address M becomes “invisible” on the path S B M C D

The Sybil attack Represents multiple identities
Disrupt geographic and multi-path routing B M1 M5 M2 M4 M3

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

Non-cooperation Node lack of cooperation, not participate in routing or packet forwarding Node selfishness, save energy for itself

La tecnología : WEP y el estándar i Seguridad en MANET Algunas soluciones

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

KN-1=H[KN], KN-2=H[KN-1]…
TESLA Overview (cont.) Each sender splits the time into intervals It then chooses random initial key (KN) 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

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 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

Assumptions Of the network Of the nodes
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 Resources of nodes may vary greatly, so Ariadne assumes constrained nodes All nodes have loosely synchronized clocks

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)

Key Setup Shared secret keys Initial TESLA 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

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

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

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 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)

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

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

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

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

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

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

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

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

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

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 G D C M3 M1 B M2 E F A

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 G D C M3 M1 B M2 E F A

Mix Nodes Node A transmits to M1 message K1(R1, K2(R2, M)) where Ki() denotes encryption using public key Ki of Mix i, and Ri is a random number G D C M3 M1 B M2 E F A

Mix Nodes M1 recovers K2(R2,M) and send to M2 G D C M3 M1 B M2 E F A

Mix Nodes M2 recovers M and sends to G G D C M3 M1 B M2 E F A

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 source-destination pair without compromising M1 and M2 both

Alternative Mix Nodes Suppose A uses M2 and M3 (not M1 and M2)
 Need to take fewer hops Choice of mix nodes affects overhead G D C M3 M1 B M2 E F A

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 information

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