FastPass: Availability Tokens to Defeat DoS

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FastPass Availability Tokens to Defeat DoS

• Presented at CMU Systems Seminar by
• Dan Wendlandt
• Work with David Andersen Adrian Perrig

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Bandwidth exhaustion attacksrequire
infrastructure support
Loss at router buffers, before reaching endhost
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Basic Idea Availability tokens

• Allow Internet destinations to provide clients
  with an availability token through an arbitrary
  out-of-band mechanism that guarantees Internet
  availability regardless of host resource capacity
  OR the number of attackers.

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Stateless Router-based CapabilitiesA useful
building block
Source
Destination
Give priority?
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Problem Denial-of-Capability

• First packet is sent without capability
• This request channel is subject to packet floods
  (DoC).

Back where we started?
NO!
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New Requirement One packet

• Instead of protecting a flow that can be
  adversely affected by even low loss percentages,
  we now must only get ONE PACKET through.

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Possible Approaches

• Dumb Routers
• Best-effort traffic, rely on probability
• Fair Routers
• Try to give everyone an equal chance
• Informed Routers
• Infrastructure is told by destinations what
  packets to prioritize

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Availability in a Next-Gen architecture ( m2m ) ?

• Many more hosts
• Diverse end-host resources (bandwidth
  computation)
• Greater cost of being unreachable
• More stringent requirements for time to establish
  a connection

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How to compare?

• Time-to-Capability (TTC)
• Robustness to uncooperative infrastructure
• Cost/complexity to deploy
• Assumptions about topology or client resources
• Scalability nature of collateral damage

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Today Incremental Improvements

• All previous schemes increase the number of
  attacker resources needed to totally deny
  availability to a destination, but do not offer
  fundamentally secure
• availability.

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Goal Setting a Higher Bar

• We want arbitrary hosts to be able to
  communicate without delay regardless of their
  location in the Internet topology or their local
  resources.
• Subject only to provisioning the purchase from
  their network service provider.

Total Network Capacity Control
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Availability Tokens

• Extra data in the capability header that proves
  to forwarding routers that the destination wishes
  to accept the request packet

Link Header
IP Header
Capability Token
Transport Level Header Data
Request Packet
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Examples

• Destinations outsource token distribution to
  Akamai, which requires proof-of-work, etc to
  provide token. Protected by bandwidth
  geographic diversity
• An online brokerage uses a one-time-password tool
  to generate tokens.
• Small company provides private key to employees
  along with VPN software.

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A flavor of three schemes

• Public Key Scheme
• Iterative Capability Discovery
• Hash-Chain Scheme

WARNING! Important Details Omitted due to
time-constraints
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Public Key Scheme

• Private key generates token as a signature,
  public key distributed to all routers.
• Routers verify signature and check for duplicate
  or expired tokens.
• Main Challenge
• Crypto cannot be DoS-able.

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Iterative Capability Discovery

• Use partial router capabilities to protect
  discovered portions of the path.
• At congested points, encrypt capabilities THROUGH
  congested router with public key of destination,
  punt it back to client.
• Dest. authorizes client by decrypting these
  capabilities.
• Iterate.

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Iterative Discovery (1)
Source
Congestion!
Destination
Encrypted with Dest. Public key
Returned to Source
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Iterative Discovery (2)
Source
Akamai
Proof of Work / Identity
Unencrypted Capability
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Iterative Discovery (1)
Source
Congestion!
Destination
Partial Capability works as token to get request
through congested router
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Lightweight Hash-Chain Scheme
How to make this work in todays architecture
routers?
Idea Replace public key crypto with symmetric,
using a shared router destination secret.
This comes at the cost of robustness to
compromised routers.
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Lightweight Hash-Chain Scheme
H_2 Hash(H_1)
AS D
AS C
AS A
AS B
AS X
AS Y
H_1 Hash(H_0)
D
Destination has secret H0
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Hash-Chain tokens

• Destination can compute all H_i, and provides
  source S with sequence of
• Hash(S-address, H_i) pairs.
• Compromised of key H_i only impacts routers at a
  radius gt i from the source.

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Thanks!

• Interested in chatting or reading a SIGCOMM
  draft? Let me know!
• danwent_at_gmail.com
• http//www.cs.cmu.edu/dwendlan/