Anonymity and Friends: Keeping the Act of Communication Private

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Anonymity and Friends Keeping the Act of
Communication Private

• Chris DuPuis
• dupuis_at_cs.washington.edu
• 8 March 2006

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Anonymity and friends

• Receiver Anonymity You can't determine who the
  message is to
• Sender Anonymity You can't tell who the message
  is from
• Unlinkability You can't tell that a message
  received by Bob was sent by Alice, or vice versa
• Plausible deniability You can't be certain that
  a message from Bob's computer is actually from
  Bob (likewise for receiving)

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Scenario 1 Email

• From "Mark Felt" ltmark.felt_at_fbi.govgt
• To "Bob Woodward" ltbob.woodward_at_washingtonpost.co
  mgt
• Subject Nixon is a crook
• Nixon is a crook. I have proof, but I can't tell
  you my real name.
• Your pal,
• Deep Throat

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Kneecap protocol
Give us your logs.
We'll NEVER give you our logs!
Break his kneecaps.
OK, here are our logs.
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Cascade weaknesses

• Similar-sized message in and out of a proxy
• Solution Pad/split all messages into
  regular-sized packets.
• Same time in and out of a proxy
• For each message, delay it a random time.
• "Mix delay"
• No forward security
• Use ephemeral TLS connections between proxies

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Message received
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Freenet Keeping the data private

• Author creates a string describing the file
• e.g. /sources/generic/video/dvd/DeCSS.c
• Author creates hash of descriptive string.
• Author feeds hash into public/private key pair
  generating algorithm
• Author encrypts file with generated private key
• Author sends file into P2P network using hash as
  filename
• User generates key pair similarly, and decrypts
  file with public key

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Freenet Finding the data anonymously

• Use the "hide in a crowd" strategy.
• Therefore, users have anonymity
• Files are all encrypted
• Retrieval keys are all cryptographic hashes.
• Therefore, user has plausible deniability as to
  what's stored on his disk drive
• But how do users know what to ask for?
• Out-of-band communication.

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Questions?