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Clarify the use of HKDF-Expand-Label. #1372

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Clarify the use of HKDF-Expand-Label. #1372

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e85d93a
Clarify the use of HKDF-Expand-Label.
ekr Feb 9, 2025
2441a34
Remove whitespace
ekr Feb 9, 2025
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6 changes: 6 additions & 0 deletions draft-ietf-tls-rfc8446bis.md
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Expand Up @@ -4319,6 +4319,12 @@ in some cases a zero-length Context (indicated by "") is passed to
HKDF-Expand-Label. The labels specified in this document are all
ASCII strings and do not include a trailing NUL byte.

Any extensions to TLS which use "HKDF-Expand-Label" use the
HkdfLabel definition associated with the version of TLS with which
they are being used. When used with this specification, that means
using HkdfLabel as defined above; when used with DTLS {{?RFC9147}} that
means using the version defined in {{RFC9147, Section 5.9}}.

Note: With common hash functions, any label longer than 12 characters
requires an additional iteration of the hash function to compute.
The labels in this specification have all been chosen to fit within
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