[3.13] gh-72570: mention the incompatibility of XOFs with HMAC (GH-136676) (#136679)

miss-islington · picnixz · web-flow · commit 8517a890cf04 · 2025-07-15T12:10:10.000Z
gh-72570: mention the incompatibility of XOFs with HMAC (GH-136676) (cherry picked from commit a02cf19) Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
diff --git a/Doc/library/hmac.rst b/Doc/library/hmac.rst
@@ -12,6 +12,9 @@
 --------------
 
 This module implements the HMAC algorithm as described by :rfc:`2104`.
+The interface allows to use any hash function with a *fixed* digest size.
+In particular, extendable output functions such as SHAKE-128 or SHAKE-256
+cannot be used with HMAC.
 
 
 .. function:: new(key, msg=None, digestmod)
