DNSSEC and DANE – E-Mail security reloaded
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This document discusses Domain Name System Security Extensions (DNSSEC) and the DNS-based Authentication of Named Entities (DANE) protocol. It describes how DANE uses DNSSEC and Transport Layer Security (TLS) records (TLSA) to authenticate TLS certificates and secure email transport (SMTP) without relying on certificate authorities. Benefits include preventing man-in-the-middle attacks and securely validating certificates through DNS rather than certificate revocation lists. The document provides instructions and examples for configuring mail servers, DNS servers, and validating TLSA records to implement DANE for email.
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DNSSEC and DANE – E-Mail security reloaded
- 1. DANE! E-Mail!Transport!Security!done!right and!https,!jabber,!PGP,!…! ! Carsten!Strotmann!(Men!&!Mice)! Patrick!Koetter!(Sys4) 1
- 2. ©!Men!&!Mice!!http://menandmice.com! SSL/TLS!world!today •a!(too)!large!number!of!certification!authorities! •whom!do!you!trust!(ultimately)?! •CA!security!can!be!breached! •Comodo,!DigiNotar,!GlobalSign!…! •False/Fake!certificates!have!been!issued! •National!Informatics!Centre!(India),!DigiNotar,!ANSSI!… 2
- 3. TLS!and!E-Mail!Server •many!mail-server!try!to!use!TLS!encryption!when! sending!data!to!other!mail!servers! •no!human!in!reach!to!decide!if!the!certificate!is!not!good! •mail!is!send!anyway!(un-authenticated!or!un-encrypted)! •DANE!is!about!fixing!this ©!Men!&!Mice!!http://menandmice.com! 3
- 5. ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 5 STARTTLS?
- 6. ©!Men!&!Mice!!http://menandmice.com! STARTTLS! STARTTLS? TLS!and!SMTP 6
- 7. ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 7 STARTTLS? STARTTLS! wrong server
- 8. ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 8 STARTTLS? STARTTLS! Men in the Middle STARTTLS? STARTTLS!
- 9. ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 9 STARTTLS? No! Men in the Middle No! STARTTLS?
- 11. ©!Men!&!Mice!!http://menandmice.com! TLSA/SMTP •Validation!of!TLS!certificates!via!DNS(SEC)! •the!hash!of!an!x509!cert!(or!the!full!certificate)! stored!in!DNS! •proof:!owner!of!the!domain!==!owner!of!the! certificate 11
- 12. ©!Men!&!Mice!!http://menandmice.com! TLSA/SMTP •the!security-level!similar!to!domain-validated!x509! certificates! •TLSA!can!be!used!to!validate!self-signed!certificates! •TLSA!can!be!used!to!validate!X509!certificates!from! certification!authorities!(Symantec,!Comodo,!StartSSL,! CACert!…) 12
- 13. ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 13 STARTTLS? STARTTLS! SMTP MTA SMTP MTA DNS TLS cert DNS
- 14. ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 14 STARTTLS? STARTTLS! SMTP MTA SMTP MTA DNS TLS cert DNS TLSA?
- 15. DNS DNS ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 15 STARTTLS? STARTTLS! SMTP MTA SMTP MTA TLSA! DNSSEC check
- 16. DNS DNS ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 16 STARTTLS! STARTTLS! SMTP MTA SMTP MTA
- 17. DNS DNS ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 17 STARTTLS? NO! Man in the Middle SMTP MTA SMTP MTA TLSA?
- 18. DNS DNS ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 18 STARTTLS? NO! Man in the Middle SMTP MTA SMTP MTA TLSA! DNSSEC check ALERT! MITM Attack
- 19. DNS DNS ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 19 STARTTLS? STARTTLS! SMTP MTA SMTP MTA TLSA? Spoofed server
- 20. DNS DNS ©!Men!&!Mice!!http://menandmice.com! TLS!and!SMTP 20 STARTTLS? SMTP MTA SMTP MTA TLSA! DNSSEC check ALERT! wrong server! STARTTLS! Spoofed server
- 21. ©!Men!&!Mice!!http://menandmice.com! Infrastructure!DNS •DNSSEC!validation!(caching!DNS!resolver)!! •BIND!9,!Unbound,!dnsmasq,!Windows!2012! •DNSSEC!signed!zones!(authoritative!DNS!Server)! •BIND!9,!NSD,!Knots,!Y.A.D.I.F.A.,!PowerDNS,!Bundy-DNS,! [Windows!2012]* 21 *!Windows!2012R2!does!not!support!the!TLSA-Record
- 22. ©!Men!&!Mice!!http://menandmice.com! Infrastructure!Mail •MTA!(Mailserver)!with!TLSA!Support!! •Postfix!2.11,!Exim!(in!development)! •TLS!certificates! •EV-certificate!(Extended!Validation)! •DV-certificate!(Domain!Validation)! •Self-signed!certificate 22
- 23. ©!Men!&!Mice!!http://menandmice.com! BIND!9!DNSSEC •enable!DNSSEC!validation: options { … dnssec-validation auto; dnssec-lookaside auto; }; 23
- 24. manual!TLSA-Record •manual!creation!of!a!TLSA!record!hash: $ openssl x509 -in mail.example.de.crt -outform DER | openssl sha256 (stdin)= 8cb0fc6c527506a053f4f14c8464bebbd6dede2738d11468dd953d7d6a3021f1 •TLSA!record: _25._tcp.mail.example.de. 3600 IN TLSA 3 0 1 ( ©!Men!&!Mice!!http://menandmice.com! 8cb0fc6c527506a053f4f14c8464bebbd6dede 2738d11468dd953d7d6a3021f1 ) 24
- 25. TLSA-Record!creation!with!tools ©!Men!&!Mice!!http://menandmice.com! •TLSA!record!using!ldns-dane: $ ldns-dane create www.bund.de 443 _443._tcp.www.bund.de. 3600 IN TLSA 3 0 1 8f28b062eaa9f917042a63d35d99e017c68d89eaa314c49a3ef94b6e770b0a49 •test!TLSA!Record!with!ldns-dane: $ ldns-dane verify www.bund.de 443 77.87.229.48 dane-validated successfully 25
- 26. ©!Men!&!Mice!!http://menandmice.com! test!TLSA-Record DNSSEC check OK shell> dig _25._tcp.mail.example.de. +dnssec +m ; <<>> DiG 9.9.5 <<>> _25._tcp.mail.example.de TLSA +dnssec +m ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 13973 ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0 26 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags: do; udp: 4096 ;; QUESTION SECTION: ;_25._tcp.mail.example.de. IN TLSA ;; ANSWER SECTION: _25._tcp.mail.example.de. 3588 IN TLSA 3 1 1 ( 8cb0fc6c527506a053f4f14c8464bebbd6dede 2738d11468dd953d7d6a3021f1 ) _25._tcp.mail.example.de. 3588 IN RRSIG TLSA 8 5 3600 ( 20140324063111 20140317121843 4390 example.de. RBgAAzQx3gks0KKJHuJ7qKd61jpY8E6dwDM6inPPa6Ee xV8OBnAzhF4RMKSabHF0LNwRzWqE5xNfPibMQFDoDRKJ /QiNgux/IXti3JqtH4BkT0w7Ooi+8DZsil9BTjg6WkaX 1FuJ4rJ2r3hXS7eIOFWtOF7pPVPdIIaRB6xp+1A= ) ;; Query time: 9 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) ;; WHEN: Mon Mar 17 19:29:45 CET 2014 ;; MSG SIZE rcvd: 142 TLSA Record DNSSEC signature
- 27. Postfix!configuration Postfix!configuration!for!TLSA!validation: shell> postconf -e "smtpd_use_tls = yes" shell> postconf -e "smtp_dns_support_level = dnssec" shell> postconf -e "smtp_tls_security_level = dane" ©!Men!&!Mice!!http://menandmice.com! 27
- 28. Postfix!log!(untrusted!TLS) Postfix!log!TLS!without!DNSSEC!TLSA!validation! (DANE): Mar 16 19:10:55 m3 postfix/qmgr[25923]: 2B1A680337: from=<root@myinfrastructure.org>, size=291, nrcpt=1 (queue active) Mar 16 19:11:03 m3 postfix/smtp[25929]: Untrusted TLS connection established to mail1.example.de[2001:db8:100::25]:25: TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits) Mar 16 19:11:05 m3 postfix/smtp[25929]: 2B1A680337: to=<benutzer@example.de>, relay=mail1.example.de[2001:db8:100::25]:25, delay=16, delays=6.2/0.01/7.9/2.1, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as 3fn80C2DP5zTT) ©!Men!&!Mice!!http://menandmice.com! Mar 16 19:11:05 m3 postfix/qmgr[25923]: 2B1A680337: removed 28
- 29. Postfix!log! (DNSSEC!secured!TLS) Postfix!log!TLS!with!DNSSEC!TLSA!validation! (DANE): Mar 16 19:20:01 m3 postfix/qmgr[26122]: 8FBEE80337: from=<root@myinfrastructure.org>, size=285, nrcpt=1 (queue active) Mar 16 19:20:01 m3 postfix/smtp[26131]: Verified TLS connection established to mail.example.de[2001:db8:100::25]:25: TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits) Mar 16 19:20:03 m3 postfix/smtp[26131]: 8FBEE80337: to=<benutzer@example.de>, relay=mail.example.de[2001:db8:100::25]:25, delay=149, delays=147/0.03/0.13/1.8, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as 3fn8BY3ltPzTT) ©!Men!&!Mice!!http://menandmice.com! Mar 16 19:20:03 m3 postfix/qmgr[26122]: 8FBEE80337: removed 29
- 30. ©!Men!&!Mice!!http://menandmice.com! DANE!TLSA!Benefits •authenticated!encrypted!connection!between!SMTP! server!!! •prevents!STARTTLS!"downgrade"!attacks! •secures!against!fake/spoofed!TLS/SSL!certificates! •no!CRL/OCSP!required!to!"revoke"!a!certificate!(just! replace!the!TLSA!record) 30
- 32. ©!Men!&!Mice!!http://menandmice.com! TLSA-Info!Webseite 32 http://tlsa.info
- 33. DANE!-!more!than!SMTP Prosody!Jabber!Server http://bridge.grumpy-troll.org/2014/05/xmpp-dane-with-prosody/ ! Gajim!Jabber!Client https://github.com/irl/gajim ©!Men!&!Mice!!http://menandmice.com! TLSA!for!HTTPS! OPENPGPKEY!—!PGP!keys!in!DNS! IPSECKEY!—!IPSEC!keys!in!DNS! SSHFP!—!SSH!server!fingerprints! S/MIME! SRV!—!DNS!Service!Discovery 33 Standards Implementations
- 36. Links!and!additional!information ©!Men!&!Mice!!http://menandmice.com! DNSWorkshop http://dnsworkshop.org! Postfix!TLS!Readme! http://www.postfix.org/TLS_README.html! Wietse!Venema!"Postfix!2.11"!FOSDEM!2014! Video!-! https://fosdem.org/2014/schedule/ event/ postfix_lessons_learned_and_recent_dev elopments/! IETF!"DANE"!Workinggroup http://datatracker.ietf.org/wg/dane/! TLSA!RFC!6698 http://datatracker.ietf.org/doc/rfc6698/! TLSA/SMTP!Draft http://datatracker.ietf.org/doc/draft-ietf-dane- smtp-with-dane/! c't!Magazin!Issue!11/2014!-!Page!194! "Geleitschutz"! c't!Magazin!Issue!18/2014!-!Page!162ff!"DANE! auf!Linux!Servern"!and!"DNSSEC!für!Clients!und! Client-Netze!einrichten"! TLSA!generator!webpage https://www.huque.com/bin/gen_tlsa! NLnetLabs!"ldns" https://www.nlnetlabs.nl/projects/ ldns/! "hash-slinger"!von!Paul!Wouters!(Red!Hat)! http://people.redhat.com/pwouters/ hash-slinger/! DNSSEC!Training! http://www.menandmice.com/support-training/ training/dnssec-workshop/ 36