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Usable Encryption Class Presentation for CMSC 818D

Wei Bai

Application

S  Hardware Encryption

S  Web Encryption S  Email Encryption

S  OpenPGP

S  S/MIME

S  Online Social Network

Public Key Encryption

S  Encryption/Decryption

S  Signing/Verifying

Prototype for Public Key Encryption

Prototype for Signing/Verifying Bob Alice

Usable Encryption Design Aspects

Design Aspects

Encryption UI

(Automatic) Encryption and

Decryption

Key Management

Integration

A. Whitten et al. “Why Johnny can’t encrypt: a usability evaluation of PGP 5.0”

S  One of the pioneer works for encryption usability

S  Objective: Investigate usability in standard UI design vs security

S  A case study of PGP 5.0 through S  Cognitive walkthrough analysis S  Lab Study

Definitions of Usability for Security

S  1. Reliably made aware of the security tasks they need to perform

S  2. Able to figure out how to successfully perform those tasks

S  3. Don’t make dangerous errors

S  4. Comfortable with the interface to continue using it.

Properties

S  1. The unmotivated user property

S  2. The abstraction property

S  3. The lack of feedback property

S  4. The barn door property

S  5. The weakest link property

Usability Standard for PGP

S  Encrypt/decrypt

S  Sign/verify

S  Key generation

S  Own public key publication

S  Public key acquiring

S  Avoid dangerous errors

S  Reasonable time

Usability Analysis

S  Cognitive walkthrough Analysis S  Wide considerations for more factors

S  Subjective

S  Lab Study S  Limited scope of factor testing

S  Objective

Cognitive analysis: Flaws in Design

S  Key management Issue S  Visual: sign/verify

S  Different key types S  RSA for PGP,

S  Hellman/DSS for PGP 5.0

S  Key server

S  Errors playing with keys. Irreversible! S  Delete the private key, publicize the private key

Lab study

S  Integrate Eudora with PGP

Lab study

S  Confirmed some points:

S  What keys to use? How to use them? S  Confused about private/public keys

S  Use own/counterpart’s keys?

Discussions

S  1. Dangerous errors and the barn door property: S  If reversible? Regret allowed?

S  2. Whether tutorials about encryption tasks, such as generating keys should be included? S  Learnability: Learn by themselves, or taught by others?

S  3. Is signing and verification necessary? S  Closed circle S  Phishing exists

S  4. How about separating encryption and decryption tasks, to make study shorter?

S. Routi et al, “Confused Johnny: when automatic encryption leads to confusion and mistakes”

S  Objective S  Investigate whether it makes more usable if hiding as many

security details as possible

S  Method: S  Lab study of Pwm (private webmail) system

Pwm Highlights

S  Automatic key management and automatic encryption

S  Integrate tightly with existing webmail services

S  Key management by a key escrow S  Advantage:

S  Automatic key management S  Users never lose their keys S  Keys ported to new devices automatically

S  Disadvantage S  Escrow has access to users’ keys

Comparative Usability Study

S  Task scenario: S  Decrypt an email first

S  Send an encrypted email

S  Open a new Gmail session (with Pwm ended)

S  Perform well compared to existing webmail tools (w.r.t. SUS score)

Key Findings

S  Performance of Message Protector is, on par with, slightly higher than Pwm.

S  Too transparent design loses trust to some extent

S  Reconsider manual encryption S  The idea also comes from “Johnny for Facebook” paper.

Discussions

S  Automatic key management by using a third party service? S  Chicken and egg problem！

S  Tradeoff between usability/security

Helping Johnny 2.0 to encrypt His Facebook conversations

S  Objective: S  Encryption usability for online social networks (OSNs)

S  Methods: S  Two lab studies

Mockup Lab Study

Mockup Lab Study

S  Encryption schemes: S  Auto/not auto: encryption button

S  Key management: S  Manual: send keys over webmail

S  Auto: Passwords created at the first time, and then web browser caches it for further use.

Key findings

S  Auto encryption and auto key management is preferable. S  Manual encryption / manual decryption have higher security

feeling, but lower acceptance

S  Key (password) recovery capability

Discussions

S  Do/show something makes users assured? S  Auto/not auto: encryption button

S  Key management: S  Manual: send keys over webmail

S  (chicken and egg problem again?)

S  Auto: Passwords created at the first time, and then web browser caches it for further use. S  Password protection? Guessibility for password is much easier

than PKI keys.