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Link Previews

The Keybase chat client offers the ability to generate previews of URLs posted in chat messages, and display them inline in the conversation thread. The client protects user privacy when generating these previews in the following ways:

  1. Allows the user to control which domains they have allowed previews to be generated for. By default, the client is configured to prompt the user for every domain of the URLs the user sends. This way, the user doesn't accidentally expose their IP address to a random link they paste into a message by mistake. A user client only visits a link if the user has explicitly granted permission to do so.
  2. Previews are completely packaged up, encrypted and sent into the chat thread with all information necessary to render the preview in all receiving clients. This way receiving clients also do not need to visit the URL to preview it, all the information is in the encrypted payload of the thread.

Prompts

Whenever a URL is sent into a chat thread, the user will be prompted to take action on it for the purposes of the link previews. The options are the following:

  1. Always - the client will always automatically generate a preview for all domains in the future.
  2. Always for domain - the client will never prompt for the specific domain again.
  3. Yes, but ask again for domain - the client will generate the preview for the current message, but will ask again for the domain.
  4. Not now - the client will not generate a preview for this message.
  5. Never - the client will never generate any preview, or prompt for them in the future.

The domain whitelist data is stored in a special hidden, "developer" chat conversation associated with the user. This allows the user to sync the domain whitelist to all of their devices without the Keybase server knowing the contents of it. The hidden chat channels get all of the same encryption and privacy of a normal chat channel, but provides the benefit of allowing the Keybase client to sync cross device in an encrypted manner.

Giphy

Giphy.com is special-cased in the Keybase client to allow for searching for GIFs to send directly from the client. We use a technique similar to Signal to safeguard user privacy for these requests as described in their blog post about the subject. The general technique is to use a TCP proxy on the Keybase server-side to anonymize the requests into Giphy.com. This has the effect of hiding the search contents from Keybase, and hiding the IP address of the user from Giphy.com. This is achieved in the following manner:

  1. Keybase client opens a TCP connection to the Keybase Giphy proxy server.
  2. Keybase client performs TLS for the giphy.com domain and certificate. This protects the data from Keybase.
  3. The Keybase proxy server opens a TCP connection to Giphy.com and begins forwarding packets to/from Giphy and the Keybase client. This protects the client from exposing its IP address to Giphy.

Giphy link previews are packaged, encrypted and sent into conversation threads in the same manner as any other link preview, so receivers will never contact the Keybase Giphy proxy or Giphy to render the content.