Dead Letters to Alice - Reachability of E-Mail Addresses in the PGP - - PowerPoint PPT Presentation

Introduction Study Design Results Conclusion

Dead Letters to Alice

• Reachability of E-Mail Addresses in the PGP

Web of Trust

Benjamin Leiding 1 Andreas D¨ ahn 2

1University of G¨

• ttingen

Telematics Group benjamin.leiding@cs.uni-goettingen.de

2University of Rostock

andreas.daehn2@uni-rostock.de

August 1, 2016

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Introduction Study Design Results Conclusion

Overview

1 Introduction 2 Study Design 3 Results 4 Conclusion

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Introduction Study Design Results Conclusion

Introduction

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Introduction Study Design Results Conclusion

PGP Web of Trust

• Decentralized trust model for

public keys

• Mainly used for encrypted email

communication

• Users sign other users’ public key

using their own private key to certify authenticity

• Interpreting each key as node and

each signature as directed edge results in a directed graph → The PGP Web of Trust

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Introduction Study Design Results Conclusion

Motivation

• Many different trust metric calculations applied to underlying

graph of the Web of Trust

• Commonly used trust metrics exclude expired/revoked keys

and signatures BUT: Reachability of corresponding email account has not been considered as a criteria so far.

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Introduction Study Design Results Conclusion

Study Design

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Introduction Study Design Results Conclusion

Study Setup

1 Preparation 2 Syntax check of e-mail addresses 3 DNS testing 4 Validation 5 E-mail account testing

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Introduction Study Design Results Conclusion

Preparation and Syntax Check

• 1. Preparation
• Keyring snapshot retrieved on October 22, 2014
• Extract e-mail addresses
• Remove duplicates
• 2. Syntax check of e-mail addresses
• Filtering for syntactical validity
• No .onion-addresses (and similar)

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Introduction Study Design Results Conclusion

DNS Testing, Validation and E-Mail Account Testing

• 3. DNS testing
• Pull each domain’s DNS record and extract mail exchange

(MX) server

• 4. Validation
• Test MX servers’ validation policy →

27d89e25a3518f4a7434474c2a7d4f1e43911bc58bec5f1@cia.gov

• 5. E-Mail account testing
• Actual testing of e-mail addresses

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Introduction Study Design Results Conclusion

Study Duration

Main-Study

• Between February 12, 2015 and July 24, 2015

Sub-Study

• Between August 11, 2015 and August 30, 2015
• Used a subset (1%) of the syntactical correct and unique

addresses

• Almost same results (88%)

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Introduction Study Design Results Conclusion

Results

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Introduction Study Design Results Conclusion

Findings - Syntactical Correct Unique E-Mail Addresses

34.7 % Account is reachable 28.0 % Account is unreachable 6.5 % Error during test 17.9 % No validation due to server policy 12.9 % Domain problem

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Introduction Study Design Results Conclusion

Findings - Server Allowed Validation

50.1 % Account is reachable 40.5 % Account is unreachable 9.4 % Error during test

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Introduction Study Design Results Conclusion

Top 5 Mail Exchange Domains

MX domain Overall Tested dead Tested alive abs. rel+ abs. abs google.com 472,528 14.84 % 64,268 369,816 googlemail.com 142,350 4.47 % 44,401 64,599 hotmail.com 125,857 3.95 % 50,036 53,128 gmx.net 106,818 3.35 % 18,943 63,796 yahoodns.net 83,747 2.63 % 745 476

+ to number of syntactic correct e-mail addresses the WoT

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Introduction Study Design Results Conclusion

Selected Mail Exchange Operating Companies

Provider Overall Tested dead Tested alive abs. rel+ abs. rel++ abs rel+++ Google 614,878 19.31 % 108,669 12.18 % 343,415 31.11% United Internet 216,999 6.82 % 49,569 5.56 % 115,479 10.46 % Microsoft 183,104 5.75 % 54,076 6.06 % 57,360 5.20 %

+ to number of syntactic correct e-mail addresses in PGP web of

trust

++ to number of e-mail addresses found unreachable in the study +++ to number of e-mail addresses found reachable in the study

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Introduction Study Design Results Conclusion

Conclusion

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Introduction Study Design Results Conclusion

Conclusion

Conclusion

• Extracted about four million e-mail addresses and tested three

million of them

• 40% of the e-mail addresses are unreachable
• 46% of the reachable e-mail addresses are operated by one of

three organizations

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Introduction Study Design Results Conclusion

Questions?

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