Initial sequence numbers
05Initial sequence numbers help distinguish connection incarnations and make blind guessing harder.
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
DIAGRAM§ 3.4.1 ↗
RFC 9293 · § 3.4.1EXAMPLE
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03
Start sequence synchronization.
The peer learns the starting sequence through the handshake.
Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
RFC 793 § 3.3RFC 9293 § 3.4.1
The base specification now incorporates the stronger RFC 6528 initial-sequence-number algorithm; RFC 9293 § 5 identifies this change.
Read the updated RFC section ↗Do not use an easily predictable starting point.
- Generate ISNs using a clock component combined with a pseudorandom function of the connection tuple and a secret.
- Keep the secret difficult to predict and manage its lifetime appropriately.
- Sequence defenses reduce some attacks; they do not provide cryptographic peer authentication.
RFC 9293 incorporates RFC 6528. The consolidation records accumulated improvements rather than introducing every one for the first time in 2022.
Read the RFC section ↗Diagrams simplify the RFC. Read the linked sections for complete requirements.
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