tree 1a8df200eab1ee6a568c2ba9498926b93c03a0ae
parent d2c3f1d8b9537a0fec2a2d4b1df405ac091cd7f3
author Filippo Valsorda <filippo@golang.org> 1540387590 -0400
committer Filippo Valsorda <filippo@golang.org> 1540503451 +0000

hkdf: add Extract and Expand

RFC 5869, Section 3.3 suggests it might be sometimes appropriate to use
Expand without Extract, and it is reasonable to reuse (secret, salt)
with different info values, in which case the Extract can be performed
once as an optimization.

TLS 1.3 also needs direct access to both Extract and Expand.

pseudorandomKey is ugly to look at, but that's intentional, as it
signals that this should have non-obvious properties to the user. The
docs will make it clear it's not the thing you should use in most cases.

Fixes golang/go#28237

Change-Id: Ib43ae8cdde0663aa4752172c39aadfb0e1c35f10
Reviewed-on: https://go-review.googlesource.com/c/144398
Reviewed-by: Adam Langley <agl@golang.org>