OpenPGPEmailSummit201512: EmailValidation

Workshop at 2nd OpenPGP Email Summit, Dec 2015 run by Nicolai Josuttis
Follow-Up: OpenPGPEmailSummit201607/EmailValidation

Approach

With this approach we want to establish a quick backward compatible solution to validate email addresses of UIDs of OpenPGP keys.

This would help to solve two major problems we have:

• People can currently easily upload faked keys (and they do)
• We have a lot of "moldered" keys (old keys not for any usage anymore)

The key approach is:

• Define a standard signature format to signal successfull email validation
  • The standard format would require to:
    • let the signature expire after 1 year
    • having a "signature notation" defining when/how/what was validated as JSON value
    • having a link to the validation policy of the validation server
  • The standard format allows email clients to process them accordingly
    • E.g.:
      • Prefer or highlight keys that hav any such signature
      • In the UI show a list of who validated the email address
      • Signal trust for a UID if it is signed by one or more (specific) validating servers
  • But even existing email clients can benefit from them:
    • According to the WebOfTrust a user can grant trust (and therefore priority) to emails with specific signatures

• Establish some initial validation servers to perform that validations on request
  • To validate: Sends email to email address in UID encrypted with the key to ensure that the one who confirms has the private key
  • Request might be implicitly triggered by email clients or explicitly triggered by sending an email
    • request shall be an email
      • to ensure that the request is signed by the owner
    • part of the email can be two hints:
      • "upload to key server"
      • "revoke signatures on old keys"
  • Validation can be done asynchonously (not hindering immediate use of a new key)

Key properties of the approach are:

• No change of existing key server infrastructure or protocol
• Existing email clients can use it
• Fast establishment possible when email clients (e.,g. enigmail) support this in a new version
• The standard format might also be used by email providers, who provide both email address and keys (e.g. Google)

• Yes, this is a CA-like approach
  • Careful selection of initial CAs
  • Options: Current SMime CAs, trusted organizations, ... ?

• This is no perfect solution, but it makes faking keys a lot harder and easier to detect
  • Solution against trolls not against secret services
  • But very important for the acceptance of OpenPGP because the naive user does not understand, why emails are not validated

Open issues:

• How to ensure that the validation request is triggered by the owner of the key?
  • To avoid spam DOS
  • Answer: explicit request by email client that supports this approach or by user sending a specific email.

• Who runs a first validation server?

Documents / Links / Resources

Initial Proposal: https://lists.gnupg.org/pipermail/gnupg-users/2015-July/053971.html

Slides: attachment:EmailValidation20151207.pdf

Whiteboard 2nd OpenPGP Email Summit: attachment:Whiteboard_EmailValidation.png

Feedback

Please send comments and feedback to Nico Josuttis, nico(at)enigmail.net (Fingerprint: CFEA 3B9F 9D8E B52D BD3F 7AF6 1C16 A70A F92D 28F5)