Presentation made by Florian Obser at NONOG 4 in Oslo, Norway on 21 September 2022

1. DNSSEC
Florian Obser | NONOG-4 | 2022-09-21

2. Florian Obser | NONOG-4 | 2022-09-21
About me
• Senior system engineer
- k.root-servers.net (AS25152)
- AuthDNS (AS197000)
- pri.authdns.ripe.net
- f-reverse
- ripe.net
- Various ccTLDs
• OpenBSD developer
- author of unwind(8)
- validating resolver, based on unbound
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3. Florian Obser | NONOG-4 | 2022-09-21
About DNS
• Globally distributed, scalable, hierarchical database
• Everything on the Internet uses it for federation
- Visiting a website
- Sending an Email
- Requesting a TLS certificate
- “Forgot my password” links
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4. Florian Obser | NONOG-4 | 2022-09-21
Problems with DNS
• No data integrity
• No authenticated data origin
• No authenticated denial of existence
• No privacy / confidentiality
- Not this talk
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5. Florian Obser | NONOG-4 | 2022-09-21
DNSSEC
• Public-key cryptography (DNSKEY)
• Signatures over authoritative data (RRSIG)
• Well known trust-anchor
- Key Signing Key of the root zone
• Delegate cryptographic authority (DS)
• Signing on zone change or RRSIG expiry, not per query
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6. Florian Obser | NONOG-4 | 2022-09-21 6
DNSViz - ripe.net

7. Florian Obser | NONOG-4 | 2022-09-21 7
DNSViz - root and .net

8. Florian Obser | NONOG-4 | 2022-09-21 8
DNSViz - ripe.net

9. Florian Obser | NONOG-4 | 2022-09-21
DNSSEC Operations
• General DNS hygiene
- No lame delegations
- Keep name servers in sync
• Time
- Synchronised clocks on signers & validators
- TTLs
- Usually long in parent zones, ~ 1+ days in TLDs
• RRSIG expiration
- Align RRSIG expiration with expire time in SOA record
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10. Florian Obser | NONOG-4 | 2022-09-21
Large answers
• IP Fragmentation
- DNS Flag Day 2020: limit UDP answers to 1232 bytes
• Amplification attacks
- Response Rate Limiting (RRL)
- Elliptic curves signatures are smaller than RSA
- NSEC answers are smaller than NSEC3 answers
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11. Florian Obser | NONOG-4 | 2022-09-21
Signing considerations
• ECDSAP256SHA256 (13) or RSASHA256 (8)
- RFC 8624: Algorithm Implementation Requirements and Usage Guidance for
DNSSEC
• KSK/ZSK vs. CSK
- KSK / ZSK
- KSK can be offline
- (Emergency) ZSK rollovers are faster
- CSK
- Zone is smaller
- Fewer moving parts if keys are online anyway
- Rollovers need to interact with parent zone
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12. Florian Obser | NONOG-4 | 2022-09-21
NSEC vs. NSEC3 vs. white-lies
• Provides authenticated denial of existence
• DNS records for “nothing exists in this interval”
• NSEC: labels are in the clear
- trivial zone enumeration
• NSEC3: labels are hashed
- susceptible to offline dictionary attacks
• white-lies: minimal interval is calculated per query
- Requires online, per-query signing
- Nothing is learned about zone contents
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13. Florian Obser | NONOG-4 | 2022-09-21
DNSSEC signing
• Fiendishly clever perl one-liner
• FOSS (alphabetical order)
- BIND
- Knot DNS
- OpenDNSSEC
- PowerDNS
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14. Florian Obser | NONOG-4 | 2022-09-21 14
AuthDNS design
Hidden Signer
Distribution Server
Distribution Server
Anycast
constellation
Zones
(RIPE DB, git)
Warm standby
Hidden Signer

15. Florian Obser | NONOG-4 | 2022-09-21
Enabling DNSSEC
• Add DS record to parent zone
- Manual at the registrar
- API
- Inline using CDS / CDNSKEY
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16. Florian Obser | NONOG-4 | 2022-09-21
Debugging DNSSEC
• Step away from the computer and panic
• Online tools
- dnsviz.net
- dnssec-analyzer.verisignlabs.com
• cli tools
- dig +dnssec +multiline +nocrypto
- delv
• DNS-OARC
- dns-operations mailing list
- Mattermost server
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17. Florian Obser | NONOG-4 | 2022-09-21
Validation
• All public quad-x resolvers validate
• FOSS (alphabetical order)
- BIND
- Knot Resolver
- PowerDNS recursor
- Unbound
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18. Florian Obser | NONOG-4 | 2022-09-21
Validator operations
• Time
- Synchronised clocks
- Make sure NTP does not depend on DNSSEC
• Monitor SERVFAIL rate
• Be prepared to put Negative Trust Anchors (NTA) in place
• Make sure middle boxes don’t interfere
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19. Questions?
fobser@ripe.net
@florian@bsd.network