Stronger Password Authentication Using Browser Extensions Blake Ross, Collin Jackson, Nick Miyake, Dan Boneh, John Mitchell Stanford University

2 Password Phishing Problem Bank A Fake Site u User cannot reliably identify fake sites u Captured password can be used at target site pwd A

3 Common Password Problem Bank A vulnerable site high security site pwd A pwd B = pwd A  Phishing attack or break-in at site B reveals pwd at A Server-side solutions will not keep pwd safe Solution: Strengthen with client-side support Site B

4 Our Solution: PwdHash u Lightweight browser extension u Impedes password theft u Invisible to server u Invisible to user  Pwd Prefix  Pwd Hashing

5 Password Hashing Bank A hash(pwd B, SiteB) hash(pwd A, BankA) Site B u Generate a unique password per site HMAC fido:123 (banka.com)  Q7a+0ekEXb HMAC fido:123 (siteb.com)  OzX2+ICiqc pwd A pwd B =

6 Password Hashing: past attempts u Hash pwd with realm provided by remote site: HTTP 1.1 Digest Authentication Kerberos 5 Does not prevent phishing, common pwd u Hash pwd with network service name: Abadi, Bharat, Marais [PTO ’97] Standalone. Gabber, Gibbons, Mattias, Mayer [FC ’97]. Proxy. Relies on intercepting traffic  can’t handle https

7 Password Hashing: a popular idea u Recent password hashing projects: u Similar hashing algorithms u Only PwdHash defends against spoofing and is invisible to the user Site Password Password Maker Genpass Passwdlet Password Composer Magic Password Generator PwdHash Password Generator Extension

8 The Spoofing Problem u JavaScript can display password fields or dialogs: u Unhashed password sent to attacker in clear

9 Password Prefix u Original pwd should never be visible to web page OzX2+ICiqc Site B

10 Password Prefix: How it works u Normal operation: Prefix in password field u Abnormal operation: Prefix in non-password field Can just ignore the prefix and not hash Remind user not to enter password   ********** abcdefgh  fido:123 HMAC fido:123 (siteb.com)  Q7a+0ekEXb

11 Why use Password Prefix? u Protection mechanism “built in” to password u Does not rely on user to make a decision u Same prefix works for everyone u Distinguishes secure passwords from normal passwords social security numbers PINs u Only use it when you want to

12 Other Trusted Pwd Interfaces u Password prefix u Secure attention sequence u Trusted image or phrase: Passmark DSS Starts with

13 Other Challenges u Password Reset u Internet Cafes u Dictionary Attacks u Spyware, DNS poisoning (no protection) u Other issues (described in the paper) Choosing salt for hash Encoding hashed password Additional attacks and defenses

14 u After install, PwdHash can’t protect existing pwds Only passwords starting with are secure User can choose where to use PwdHash User must enter old password unhashed into password reset page u Pwd Prefix makes it easy Old passwords won’t be accidentally hashed New, secure passwords are automatically hashed Password Reset Starts with

15 Internet Cafes u Users cannot install software at Internet Cafes. u Would not be a problem if PwdHash were universally available u Interim solution: A secure web site for remote hashing, e.g. u Hash is computed using JavaScript Server never sees password Resulting hash is copied into clipboard Can also be used as a standalone password generator Internet Explorer Firefox

16 Dictionary attacks u After phishing attack or break-in to low security site, attacker can repeatedly guess password and check hash. Succeeds on  15% of passwords (unlike 100% today) Less effective on longer, stronger passwords u Solution: better authentication protocol (SPEKE, SRP, etc.) Requires server-side changes u Defense: user specifies a global pwd to strengthen all pwd hashes Creates a new pwd management problem for shared machines u Defense: slow hash function (Halderman, Waters, Felten ‘05) Increases time of dictionary attack aardvark, aback, abacus, abandon…

17 PwdHash: Try it out u Prototype for Internet Explorer and Mozilla Firefox u Defends against spoofing u Invisible to user u Invisible to server u Complementary to other anti-phishing solutions u Only use it when you want to