Easy To Use Secure Mail

1. ISRL Internet Security Research Lab http://isrl.cs.byu.edu Easy To Use Secure Mail Tim van der Horst Kent Seamons seamons@cs.byu.edu

2. Email is a postcard • Almost all email is sentin the clear • Email provider can access stored messages • Users increasingly trust online service providers to store their email • Google, Yahoo, Hotmail, etc.

3. Encrypted email • Encrypted email solves the postcard problem • Current solutions • PGP • S/MIME • No widespread adoption • Hard to get keys for self and recipients • Many users don’t know what encryption is, or how to use it

4. Our solution

5. Sender • Download and install an email plug-in • Prove her identity to the key server • Receive an email message from the key server • Happens once per email address • No more interaction required with key server to send secure messages to any recipient • Simply specify the email address of the recipient and send secure email messages • The email contents are encrypted and sent to the recipient as an attachment, along with plain-text instructions in the body of the message indicating where to obtain software to decrypt the message

6. Recipient • First-time receipt of encrypted message • The sender and subject line of the message are in plain text • The plaintext body informs the recipient that the message attachment is encrypted and refers the user to a plug-in needed to decrypt the message • The recipient installs the plug-in • Recipient proves her identity to the key server • Receive an email message from the key server • Happens once per email address • Decrypt a secure email messages • Click on the message in the inbox to read the messages • Client software obtains decryption key from the key server based on sender’s and recipient’s email address. The key can be cached at the client. • Message is decrypted and displayed to the user.

7. How our secure email works KDF(x)

8. Security analysis • Trust model • Key escrow • Key server can derive all keys • Messages don’t pass through the key server • Business can host their own key server • Threats • Basic model thwarts passive observation • Vulnerable to some impersonation attacks • Due to how key server authenticates a user’s ability to receive an email message • Use of a stronger authentication mechanism eliminates this weakness • The design supports a dial for convenience/security

9. Prototypes • 3rd party key server • Crypto card to protect master key • Clients • Firefox extension for Gmail • Web mail • Thunderbird extension • Standard email client • Java applet • Loosely coupled with any email client • Available to a user for any client that does not have a plug-in available for secure email

10. Future plans • Host a key server for public use • Popular email clients • Web: Gmail, Yahoo, Hotmail, AOL • Traditional: Thunderbird, Outlook, Lotus Notes • User studies • Obtain feedback from users to guide design decisions