diff --git a/Doc/library/hmac.rst b/Doc/library/hmac.rst index d6692033b2d4c3..57076c38086c79 100644 --- 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)