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Interdomain Routing Security. Jennifer Rexford Advanced Computer Networks Tuesdays/Thursdays 1:30pm-2:50pm. Outline. Security goals for interdomain routing Secure message exchange Prefix ownership and attributes

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Interdomain routing security l.jpg

Interdomain Routing Security

Jennifer Rexford

Advanced Computer Networks

Tuesdays/Thursdays 1:30pm-2:50pm

Outline l.jpg

  • Security goals for interdomain routing

    • Secure message exchange

    • Prefix ownership and attributes

    • Agreement with the forwarding path

    • Preventing resource exhaustion

  • BGP (in)security today

    • Best common practices

  • Proposed security enhancements

    • Secure BGP (S-BGP)

    • Anomaly-detection schemes

  • Discussion

Secure message exchange between neighbors l.jpg

BGP session

physical link

Secure Message Exchange Between Neighbors

  • Confidential BGP message exchange

    • Can two ASes exchange messages without someone watching?

  • No denial of service

    • Prevent CPU overload, session reset, and tampered BGP messages?

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Validity of Route Announcements

  • Origin authentication

    • Is the prefix owned by the AS announcing it?

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Validity of Route Announcements

  • AS path authentication

    • Is AS path the sequence of ASes the BGP update traversed?

“4 6”

“7 5 6”

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Adherence to Business Contracts

  • AS path policy

    • Does the AS path adhere to the routing policies of each AS?

    • Is a path announced when it should be?



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Correspondence to the Data Path

  • Agreement between control and data plane

    • Does the traffic follow the advertised AS path?

“4 5 6”

“7 5 6”

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Preventing Resource Exhaustion

  • Limiting the size of the BGP table

    • Can the router run out of memory?

    • Storing routes for many prefixes, with long paths?

  • Limiting the number of BGP messages

    • Can the router run out of CPU and bandwidth?

    • Due to flapping prefixes, duplicate messages, etc.

BGP sessions

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BGP Security: Applying Best Common Practices

  • Securing the BGP session

    • Authentication, encryption, TTL tricks

  • Filtering routes by prefix and AS path

    • Preventing your customers from hijacking others

  • Resetting attributes to default values

    • Preventing your peers from tricking you

  • Packet filters to block unexpected BGP traffic

    • Blocking port 179 from unexpected places

  • Preventing resource exhaustion

    • Limiting #prefixes/session, and prefix lengths

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Best Practice is Not Good Enough

  • Depends on vigilant application of BCPs

    • By your neighbors, and your neighbors’ neighbors, and your neighbors’ neighbors’ neighbors

    • And nobody making configuration mistakes!

  • Doesn’t address fundamental problems

    • Can’t tell who owns the IP address block

    • Can’t tell if the AS path is bogus or invalid

    • Can’t be sure data packets follow the chosen route

    • Can’t easily bound the memory requirements

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Secure BGP (S-BGP)

  • Address attestations

    • Claim the right to originate a prefix

    • Signed and distributed out-of-band

    • Checked through delegation chain from ICANN

  • Route attestations

    • Distributed as an attribute in BGP update message

    • Signed by each AS as route traverses the network

    • Signature signs previously attached signatures

  • S-BGP can validate

    • AS path indicates the order ASes were traversed

    • No intermediate ASes were added or removed

S bgp deployment challenges l.jpg
S-BGP Deployment Challenges

  • Complete, accurate registries

    • E.g., of prefix ownership

  • Public Key Infrastructure

    • To know the public key for any given AS

  • Cryptographic operations

    • E.g., digital signatures on BGP messages

  • Need to perform operations quickly

    • To avoid delaying response to routing changes

  • Difficulty of incremental deployment

    • Hard to have a “flag day” to deploy S-BGP

S bgp l.jpg

  • Prevents many threats

    • Prefix hijacking

    • Route modification

  • But not others

    • Collusion: two ASes claiming to have an edge

    • Policy violation: distributing a route from one provider to another

    • Data-plane attacks: announcing one path but using another

    • Resource exhaustion: announcing too many routes

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Anomaly-Detection Schemes

  • Monitoring BGP update messages

    • Use past history as an implicit registry

    • E.g., AS that announces each address block

    • E.g., AS-level edges and paths

  • Out-of-band detection mechanism

    • Generate reports and alerts

    • Internet Alert Registry:

    • Prefix Hijack Alert System:

  • Soft response to suspicious routes

    • Prefer routes that agree with the past

    • Delay adoption of unfamiliar routes when possible

    • Some (e.g., misconfiguration) will disappear on their own

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Anomaly-Detection Schemes

  • Risk of false positives

    • Temporarily (?) avoiding legitimate routes

  • Risk of false negatives

    • Possibly vulnerable to a smart adversary

  • Can detect some paths S-BGP cannot

    • E.g., announcing from one provider to another

  • Does not prevent all attacks

    • Does not prevent collusion or data-plane attacks

  • More amenable to incremental deployment

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Security Goals

  • What kind of attacks should we withstand?

    • Misconfiguration?

    • Control-plane adversary?

    • Colluding adversaries?

    • Data-plane adversaries?

  • What solution would we want, from scratch?

    • S-BGP?

    • Data-plane path verification?

    • Multipath routing?

  • What kind of solution can be deployed?

    • S-BGP? Anomaly detection? Multipath routing?

Conclusions l.jpg

  • BGP is highly vulnerable

    • Based on trust, even of ASes many hops away

  • BGP security is a serious problem

    • Blackholing, snooping, impersonating, spamming

  • Defining the threat is challenging, too

    • Control-plane validation or much, much more?

  • Incremental deployment is a real challenge

    • Bootstrapping a PKI (though this has improved)

  • Still a very active area of research

    • E.g., Sharon Goldberg’s guest lecture on 11/20

Encrypting and decrypting with keys l.jpg
Encrypting and Decrypting With Keys

  • Encrypt to hide message contents

    • Transforming message contents with a key

    • Message cannot be read without the right key

  • Symmetric key cryptography

    • Same secret key for encrypting and decrypting

    • … makes it hard to distribute the secret key

  • Asymmetrical (or public key) cryptography

    • Sender uses public key to encrypt message

      • Can be distributed freely!

    • Receiver uses private key to decrypt message

Authenticating the sender and contents l.jpg
Authenticating the Sender and Contents

  • Digital signature for authentication

    • Data attached to the original message

      • … to identify sender and detect tampering

    • Sender encrypts message digest with private key

    • Receiver decrypts message digest with public key

      • … and compares with message digest it computes

  • Certificate

    • Collection of information about a person or thing

      • ... with a digital signature attached

    • A trusted third party attaches the signature

Public key infrastructure pki l.jpg
Public Key Infrastructure (PKI)

  • Problem: getting the right key

    • How do you find out someone’s public key?

    • How do you know it isn’t someone else’s key?

  • Certificate Authority (CA)

    • Bob takes public key and identifies himself to CA

    • CA signs Bob’s public key with digital signature to create a certificate

    • Alice can get Bob’s key and verify the certificate with the CA

  • Register once, communicate everywhere

    • Each user only has the CA certify his key

    • Each user only needs to know the CA’s public key

Secure origin bgp sobgp l.jpg
Secure Origin BGP (soBGP)

  • Design requirements

    • Incrementally deployable

    • Distributed Web of trust

    • Scalability by advertising security info only once

    • Trade-off level of security vs. convergence speed

  • Verify the AS path is not bogus

    • Verify the origin AS is authorized to originate

    • Verify the AS path is a valid path to origin AS

  • BGP Security message

    • Security information carried inside the protocol

    • New message; no changes to existing messages

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Certificates in Secure Origin BGP (soBGP)

  • Entity: establish identity of the AS

    • Public key for the AS, and the AS number itself

    • Signature created using the AS’s private key

  • Authentication: assign/delegate address space

    • Address ranges an AS can advertise, and the AS number

    • AS validating that the AS can advertise

      • E.g., AS owning can validate another for

    • Signature created by the validating AS’s private key

  • Policy: define policies and connectivity

    • A list of ASes that an AS attaches to

    • Routing policies applied by the AS

    • Signature created using the AS’s private key

Using sobgp l.jpg
Using soBGP

  • Upon receiving a BGP announcement

    • Can validate information in the BGP updates

    • … using information in PolicyCerts and AuthCerts

  • Obtaining the certificates

    • From new BGP Security message type

    • Gathered from well-known Web site

      • Though you have to be able to route to the Web site!

  • Flexible processing order

    • Fast convergence: route handling 1st, security 2nd

    • High security: security 1st, during route handling

Pros and cons of sobgp l.jpg
Pros and Cons of soBGP

  • Advantages

    • Provides origin authentication

    • Incrementally deployable

    • Doesn’t interfere with BGP message processing

  • Disadvantages

    • Path authentication requires a topology database

    • Policy checking requires a policy database

    • Doesn’t ensure the data path follows the BGP path

      • Though, in fairness, this is true for all of the proposals