Usable Encryption Class Presentation for CMSC 818D Wei Bai S - - PowerPoint PPT Presentation

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Usable Encryption

Class Presentation for CMSC 818D Wei Bai

Application

S Hardware Encryption S Web Encryption

S Email Encryption

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OpenPGP

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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

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RSA for PGP,

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Hellman/DSS for PGP 5.0 S Key server S Errors playing with keys. Irreversible!

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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

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• 1. Dangerous errors and the barn door property:

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If reversible? Regret allowed?

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• 2. Whether tutorials about encryption tasks, such as generating keys should be

included?

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Learnability: Learn by themselves, or taught by others?

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• 3. Is signing and verification necessary?

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Closed circle

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Phishing exists

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• 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:

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Automatic key management

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Users never lose their keys

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Keys ported to new devices automatically S Disadvantage

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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

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(chicken and egg problem again?) S Auto: Passwords created at the first time, and then web

browser caches it for further use.

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Password protection? Guessibility for password is much easier than PKI keys.