From d1648b4d7a2e045bc8ee81f666627d6a792564d6 Mon Sep 17 00:00:00 2001
From: Werner Koch <wk@gnupg.org>
Date: Thu, 25 May 2000 16:28:04 +0000
Subject: See ChangeLog: Thu May 25 18:39:11 CEST 2000  Werner Koch

---
 doc/gcryptref-digest.sgml | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

(limited to 'doc')

diff --git a/doc/gcryptref-digest.sgml b/doc/gcryptref-digest.sgml
index f0d5efff4..a123c9b25 100644
--- a/doc/gcryptref-digest.sgml
+++ b/doc/gcryptref-digest.sgml
@@ -65,7 +65,10 @@
 	     </indexterm>
   <function>gcry_md_open</function> creates the context required for
   the message digest functions.  The hash algorithm may optionally be
-  specified.
+  specified. It is possible to use these functions as MAC functons; therefore
+  the flag <literal/GCRY_MD_FLAG_HMAC/ must be given along with the
+  hash functions.  Other MAC algorithms than  HMAC are currently not
+  supported.  The key for the MAC must be set using the gcry_md_setkey macro.
   <function>gcry_md_close</function> releases all resources associated
   with the context.
   <function>gcry_md_enable</function> may be used to enable hash
@@ -149,6 +152,7 @@
   <refnamediv>
     <refname>gcry_md_ctl</refname>
     <refname>gcry_md_final</refname>
+    <refname>gcry_md_setkey</refname>
     <refpurpose>perform special operations on a digest context</refpurpose>
   </refnamediv>
 
@@ -179,9 +183,18 @@
   </para>
   <para>
   Currently defined values for <parameter>cmd</> are:
-    <literal>GCRYCTL_FINALIZE</> and the conevnience macro
+  </para>
+  <para>
+    <literal>GCRYCTL_FINALIZE</> and the convenience macro
     <function>gcry_md_final(a)</>
   </para>
+  <para>
+    <literal>GCRYCTL_SET_KEY</> and the convenience macro
+    <function>gcry_md_setkey(a)</>.  This is used to turn these
+    hash functions into MAC functions.	The key may be any string
+    of the speicified length.  The type of the MAC is determined
+    by special flags set with the open function.
+  </para>
 </refentry>
 
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