Is DANE the Future of Secure Mail? Evaluation of DNS-based - PowerPoint PPT Presentation

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Is DANE the Future of Secure Mail? Evaluation of DNS-based Authentication of Named Entities in the Context of Electronic Mail Security Stefan Fochler April 7, 2016 Chair for Network Architectures and Services Department of Informatics Technische Universit¨ at M¨ unchen Stefan Fochler – Is DANE the Future of Secure Mail? 1

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Motivation for Enhancing Email Transport Security Background on Security Goals & Email Lifecycle Analysis of Methods for Email Security Improving Email Transport Security with DANE Evaluation of DANE Conclusion Stefan Fochler – Is DANE the Future of Secure Mail? 2

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Motivation for Enhancing Email Transport Security Stefan Fochler – Is DANE the Future of Secure Mail? 3

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Motivation for Enhancing Email Transport Security ◮ Email is used for a lot of sensitive information ◮ Email Transport over SMTP uses optimistic encryption ◮ Can be intervened easily during handshake ◮ Large portions of email get transported unencrypted ◮ What mechanisms can be introduced to secure Email transport? Stefan Fochler – Is DANE the Future of Secure Mail? 4

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Background on Security Goals & Email Lifecycle Stefan Fochler – Is DANE the Future of Secure Mail? 5

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Security Goals Confidentiality ◮ Protect data from being visible to unauthorized parties ◮ Assumes passive attacker model ◮ Differenciate between contents and meta-data Stefan Fochler – Is DANE the Future of Secure Mail? 6

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Security Goals Confidentiality ◮ Protect data from being visible to unauthorized parties ◮ Assumes passive attacker model ◮ Differenciate between contents and meta-data Integrity & Authenticity ◮ Data read by receiver equal to data sent? ◮ Modifications to message have to be detected or prevented ◮ Usage of digital signature schemes can provide both integrity and authenticity Stefan Fochler – Is DANE the Future of Secure Mail? 6

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Security Goals Availability ◮ Mail infrastructure is critical ◮ Profitable target to Denial-of-Service attacks ◮ Unsolicited Commercial Email poses challenges to availability ◮ (Typically) only little application-layer protection Stefan Fochler – Is DANE the Future of Secure Mail? 7

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Lifecycle Origin MUA Destination MUA Internet Stefan Fochler – Is DANE the Future of Secure Mail? 8

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Lifecycle Origin MUA Destination MUA Internet Origin MSA/MTA Destination MRA/MDA Stefan Fochler – Is DANE the Future of Secure Mail? 8

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Lifecycle Origin MUA Destination MUA creation Internet Origin MSA/MTA Destination MRA/MDA Stefan Fochler – Is DANE the Future of Secure Mail? 8

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Lifecycle Origin MUA Destination MUA submission Internet Origin MSA/MTA Destination MRA/MDA Stefan Fochler – Is DANE the Future of Secure Mail? 8

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Lifecycle Origin MUA Destination MUA submission Internet processing & storage Origin MSA/MTA Destination MRA/MDA Stefan Fochler – Is DANE the Future of Secure Mail? 8

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Lifecycle Origin MUA Destination MUA submission Internet transfer Origin MSA/MTA Destination MRA/MDA Stefan Fochler – Is DANE the Future of Secure Mail? 8

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Lifecycle Origin MUA Destination MUA submission Internet processing & storage Origin MSA/MTA Destination MRA/MDA Stefan Fochler – Is DANE the Future of Secure Mail? 8

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Lifecycle Origin MUA Destination MUA submission retrieval Internet Origin MSA/MTA Destination MRA/MDA Stefan Fochler – Is DANE the Future of Secure Mail? 8

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Analysis of Methods for Email Security Stefan Fochler – Is DANE the Future of Secure Mail? 9

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Security Measures End-to-End Encryption ◮ Secure/Multipurpose Internet Mail Extensions (RFC 5751) ◮ Signatures and encryption based on certificates ◮ OpenPGP (RFC 4880) ◮ Cross-signed keys instead of certificate authorities Stefan Fochler – Is DANE the Future of Secure Mail? 10

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Email Security Measures End-to-End Encryption ◮ Secure/Multipurpose Internet Mail Extensions (RFC 5751) ◮ Signatures and encryption based on certificates ◮ OpenPGP (RFC 4880) ◮ Cross-signed keys instead of certificate authorities Mail Origin Safeguarding ◮ Sender Policy Framework (SPF) & DMARC (RFC 7208 & 7489) ◮ Whitelist hosts for sending mail ◮ Request reports for unsolicited email ◮ DomainKeys Identified Mail (DKIM) (RFC 6376) ◮ Email signatures ◮ Domain’s public key in DNS Stefan Fochler – Is DANE the Future of Secure Mail? 10

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Active Attacks on Email Transport Security STARTTLS Stripping ◮ SMTP negotiates encryption using the STARTTLS command (optimistic encryption) ◮ ISPs or network security hardware remove or invalidate this command ◮ No integrity protection availabile to detect this attack ◮ [6] found up to 96,13 % stripping in Tunesia in 2015 Stefan Fochler – Is DANE the Future of Secure Mail? 11

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Active Attacks on Email Transport Security STARTTLS Stripping ◮ SMTP negotiates encryption using the STARTTLS command (optimistic encryption) ◮ ISPs or network security hardware remove or invalidate this command ◮ No integrity protection availabile to detect this attack ◮ [6] found up to 96,13 % stripping in Tunesia in 2015 DNS Hijacking ◮ Public DNS servers or integrated DNS servers ◮ Deliver fraudulent IP addresses for MX records ◮ Third-party mail servers can man-in-the-middle the intended connection ◮ 2 % of public DNS servers affected [6] Stefan Fochler – Is DANE the Future of Secure Mail? 11

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Improving Email Transport Security with DANE Stefan Fochler – Is DANE the Future of Secure Mail? 12

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Idea DNS-based Authentication of Named Entities (DANE) [5] ◮ Mechanism to make TLS connections more secure ◮ Use DNS to express Certificate Assertions using entries of type TSLA ◮ Use DNSSEC for security and specific behaviour to avoid downgrading Stefan Fochler – Is DANE the Future of Secure Mail? 13

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen DNS Setup Requirements (1) [2] 1. DANE must support multiple services differenciated by port and transport mechanism on one host Stefan Fochler – Is DANE the Future of Secure Mail? 14

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen DNS Setup Requirements (1) [2] 1. DANE must support multiple services differenciated by port and transport mechanism on one host Solutions (1) 1. Introduce scheme for DNS record expressing Certificate Assertions: Prefix with port and transport 443. tcp.example.com. ... ◮ 25. tcp.mail.example.com ... ◮ Stefan Fochler – Is DANE the Future of Secure Mail? 14

Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Certificate Assertions Requirements (2) [2] 2. DANE must support asserting the specific certificate authority for this domain 3. DANE must support asserting the use of a specific certificate for this domain 4. DANE must support presenting a self-signed certificate that does not come from a well-known CA 1 1 Note the security implications of this [2, p. 8] Stefan Fochler – Is DANE the Future of Secure Mail? 15