Separate keys for separate jobs
02HKDF derives a sequence of secrets with distinct purposes instead of one reusable connection key.
This guide explains the 2018 publication. Superseded by RFC 9846.
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
DIAGRAM§ 7.1 ↗
RFC 8446 · § 7.1EXAMPLE
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Advance one sending direction.
The next traffic secret is derived from the current application traffic secret.
Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
Read the updated RFC section ↗
Handshake, application, and resumption secrets have different jobs.
- The key schedule combines PSK and (EC)DHE inputs where applicable.
- Client and server traffic secrets are distinct.
- KeyUpdate advances an application traffic secret; old receiving keys are deleted after switching.
The examples simplify the wire representation. Follow the linked specification and application profile for implementation.
Read the RFC section ↗Diagrams simplify the RFC. Read the linked sections for complete requirements.
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