BGP Joeri de Ruiter Agenda BGP recap BGP security RPKI / ROA - - PowerPoint PPT Presentation

Advanced Network Security

BGP

Joeri de Ruiter

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Agenda

• BGP recap
• BGP security
• RPKI / ROA
• BGPsec
• Startng (almost) from scratch

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Autonomous systems (AS)

• Internet is divided into Autonomous Systems (AS)
• Controlled by a single entty
• Difgerent types of AS
• Stub

– Can be mult-homed

• Transit
• ASes can connect using peering or transit relatonships
• Internet exchanges (IX)
• Basically a big switch

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Border Gateway Protocol (BGP)

• BGP-4, RFC 4271
• Used to route trafc between ASes
• Glues together the Internet
• Exchange routng informaton between autonomous systems
• Once connected to a peer, the full BGP routng tables are exchanged
• Afuerwards updates are sent when table changes

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BGP

• BGP route consists of
• Prefx
• Origin

– How the prefx was introduced into BGP

• AS Path

– Used for loop detecton and selecton of route

• Next hop

– Where to send packets for the advertsed prefx next

• Optonal parameters

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BGP example

• Router D announces prefx x to router C using eBGP:
• AS-PATH: AS3, NEXT-HOP: n
• Router B learns about new path through iBGP
• Router B announces prefx x to router A using eBGP:
• AS-PATH: AS2 AS3, NEXT-HOP: l

AS1 AS2 AS3 Prefx x A B C D k l m n

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BGP example

• Two peering links between AS2 and AS3
• Router D announces prefx x to router C using NEXT-HOP n
• Router F announces prefx x to router E using NEXT-HOP p
• Router B learns about new paths through iBGP
• Using intra-AS routng determines cost of the path to both n and p
• Store cheapest path in local routng table

AS1 AS2 AS3 Prefx x A B C D k l m n E F

• p

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BGP

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BGP

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BGP security

• BGP plaintext and unauthentcated
• Hijacking or intercepton of prefxes
• Announce longer prefx or shorter path
• Incidents occur on a daily basis

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Atacking Tor

• BGP hijacking or intercepton can be used to de-anonymise users using trafc

analysis

• RAPTOR: Routng atacks on privacy in Tor by Sun et al.
• Atacker only needs to observe any directon of trafc at both ends

Source: RAPTOR: Routng Atacks on Privacy in Tor, Sun et al., 2015

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Atacking Tor

• Feasability shown in experiment

Source: RAPTOR: Routng Atacks on Privacy in Tor, Sun et al., 2015

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BGP security

• What security propertes do we want?
• Origin authentcaton
• You can only announce prefxes that are assigned to you
• Path authentcaton
• The complete path to the origin is verifable

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Resource PKI (RPKI)

• Deployment started in 2011
• Described in RFC 6480
• Makes use of existng standards
• E.g. X.509 certfcates, extended with atributes to include IP prefxes
• Certfcates used to assign prefxes
• Root CAs called Trust Anchor
• Leaf certfcates called End-Entty Certfcates
• Route Origin Authorizaton (ROA)
• Bind prefx to AS
• Signed owner of the prefx
• One-to-one mapping between End-Entty Certfcate and ROA

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RPKI hierarchy

IANA AFRINIC APNIC ARIN LACNIC RIPE NCC LIR LIR LIR ISP ISP ISP

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Origin authentcaton

• Described in RFC 6493
• Cryptographic verifcaton performed by RPKI Cache (local or at service provider)
• Download records from repository (e.g. RIRs such as RIPE)
• Verify chain, including assigned resources
• Assigned resources should be a subset of the parent’s resources
• Verifcaton against BGP announcement performed by routers
• Router retrieves stripped ROAs from RPKI Cache
• Match BGP announcements against published ROAs

– Valid / Invalid / NotFound

• Verifcaton results used in policy
• Atacks stll possible
• Depends on how routes are chosen

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Path authentcaton

• BGPsec
• RFCs published last September
• RFC 8205
• Uses RPKI
• AS-Path authentcated using signature in BGPsec-Path
• Every AS adds signature over previous signature and newly added path

informaton

• Including next AS

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Path authentcaton - example

AS1

key1

AS2

key2

AS3

Prefx: 131.155.0.0/16 AS-Path: AS1 BGPsec: (key1, signature1) 131.155.0.0/16 AS1, AS2 Prefx: 131.155.0.0/16 AS-Path: AS1 BGPsec: (key1, signature1) BGPsec: (key2, signature2) signature1 AS2, AS3

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Startng from scratch

• Main problem is legacy
• Adopton of new standards is very slow
• Can we do beter if we start (almost) from scratch?
• Scalability, Control, and Isolaton On Next-generaton Networks (SCION)
• Started in 2009 at CMU

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SCION - Architecture

• Autonomous systems grouped into Isolaton domains (ISDs)
• ISD core
• Trust Root Confguraton (TRC)

– Version number – List of trusted root public keys

• Within AS
• Path server
• Beaconing server
• Certfcate server

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SCION - Architecture

Source: The SCION Internet Architecture: An Internet Architecture for the 21st Century, Barrera et al., 2017

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SCION – Intra-ISD path discovery

• Path Constructon Beacons (PCBs) sent using mult-path fooding
• Initalised by core nodes
• Extended and forwarded by receiving ASes
• Add incoming and outgoing interface and optonal peerings
• Eventually all nodes know how ISD core can be reached
• AS registers preferred down-segments (path from core to AS) with path

server in the core

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SCION – Path discovery

Source: The SCION Internet Architecture: An Internet Architecture for the 21st Century, Barrera et al., 2017

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SCION – Path discovery

Source: The SCION Internet Architecture: An Internet Architecture for the 21st Century, Barrera et al., 2017

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SCION – Path Constructon Beacons

• Path Constructon Beacons are signed by every AS along the path
• Can be verifed within ISD
• Hop-felds (HF) can be used to later select paths
• Contain MAC computed using hop-feld key
• Only processed locally

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SCION – Path Constructon Beacons

Source: SCION: A Secure Internet Architecture, Perrig et al., 2017

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SCION - Routng

• Path constructon performed by end nodes
• Path informaton included in packet headers
• No forwarding informaton necessary at routers
• Packet-carried forwarding state (PCFS)
• Sender decides on the path
• Typically use multple paths
• Recipient address no longer used to route between autonomous systems
• Only used by the destnaton AS

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SCION - Routng

• Path can consist of three parts
• Up-segment
• Core-segment
• Down-segment
• Segments retrieved from local path server
• Local path server queries core path server for unknown segments
• Hop-felds are for selected path are combined and included in the SCION

packet header

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SCION - Routng

Source: SCION: A Secure Internet Architecture, Perrig et al., 2017

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SCION - Routng

Source: SCION: A Secure Internet Architecture, Perrig et al., 2017

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SCION - Security

• Trust within ISD
• Compromise is kept locally → root key can only be used to compute

certfcates for local ISD

• ISD signs Trust Root Confguraton of connected ISDs
• Provides global verifability through chain of trust
• Update to the TRC propagates within minutes
• Three PKIs
• Control-plane
• Name-resoluton
• End-entty

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SCION - Security

• Control-plane
• Comparable to RPKI
• Short-lived certfcates for ASes
• Name-resoluton
• Comparable to DNSSEC
• Typically ISD will delegate name resoluton to TLDs
• End-entty
• Comparable to TLS
• Certfcates need to be signed by multple CAs and registered at publicly

verifable log server

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SCION – Name-resoluton security

Source: SCION: A Secure Internet Architecture, Perrig et al., 2017

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SCION – Data plane authentcaton

• So far, authentcaton was provided in the control place
• Authentcaton can also be provided in the data plane.
• For example using:
• OriginValidaton, packet originates from source
• PathTrace, packet followed indicated trace
• Origin and Path Trace (OPT)

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SCION - OriginValidaton

• Source shares a symmetric key with every AS on the path
• Additonal informaton in header
• DataHash: hash over payload
• SessionID: session identfer picked by source
• List of OV values: MAC over DataHash with key shared between source

and AS or destnaton

• Every intermediate AS and the destnaton verify its corresponding OV value
• Overhead linear in number of ASes on the path

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SCION - PathTrace

• Source and destnaton share a symmetric key with every AS on the path
• Additonal informaton in header
• DataHash: hash over payload
• SessionID: session identfer picked by source
• PVF: MAC over DataHash and previous value of PVF
• Every intermediate AS updates the PVF value
• Overhead constant
• Destnaton can compute MAC over data hash and fnal PVF for source to

verify path

• Verifcaton can be performed later: retroactve-PathTrace

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Summary

• BGP provides no secure by default
• Hijacking and intercepton possible
• Origin authentcaton provided by RPKI and RAOs
• BGPsec introduces path authentcaton
• SCION introduces a new architecture that provides more security by design

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Further actvites

• Read the following paper:

The SCION Internet Architecture - An Internet Architecture for the 21st Century

David Barrera, Laurent Chuat, Adrian Perrig, Raphael M. Reischuk, Pawel Szalachowski Communicatons of the ACM 60 (6), June 2017

• Optonal reading:

RAPTOR: Routng atacks on privacy in Tor

Yixin Sun, Anne Edmundson, Laurent Vanbever, Oscar Li, Jennifer Rexford, Mung Chiang, and Prateek Mital Usenix Security, 2015