X-Git-Url: https://git.openssl.org/?p=openssl.git;a=blobdiff_plain;f=doc%2Fman3%2FHMAC.pod;h=a9bcd0e6df818b16253e95362ae0ebcd6f23a5a7;hp=5c851c1f5c5656e449e5128aabf26978103c6d68;hb=b1d14c412a0ff06d191ef5640bd90bbcd590035c;hpb=4746f25ac62e5bbdc07eedcec9c9a27547577141

diff --git a/doc/man3/HMAC.pod b/doc/man3/HMAC.pod
index 5c851c1f5c..a9bcd0e6df 100644
--- a/doc/man3/HMAC.pod
+++ b/doc/man3/HMAC.pod
@@ -63,7 +63,9 @@ If B<md> is NULL, the digest is placed in a static array.  The size of
 the output is placed in B<md_len>, unless it is B<NULL>. Note: passing a NULL
 value for B<md>  to use the static array is not thread safe.
 
-B<evp_md> can be EVP_sha1(), EVP_ripemd160() etc.
+B<evp_md> is a message digest such as EVP_sha1(), EVP_ripemd160() etc. HMAC does
+not support variable output length digests such as EVP_shake128() and
+EVP_shake256().
 
 HMAC_CTX_new() creates a new HMAC_CTX in heap memory.
 
@@ -91,7 +93,7 @@ because reuse of an existing key with a different digest is not supported.
 
 HMAC_Init() initializes a B<HMAC_CTX> structure to use the hash
 function B<evp_md> and the key B<key> which is B<key_len> bytes
-long. 
+long.
 
 HMAC_Update() can be called repeatedly with chunks of the message to
 be authenticated (B<len> bytes at B<data>).