Add some documentation about the EVP_PKEY MAC interface

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/12637)

1 files changed, 41 insertions, 0 deletions

diff --git a/doc/man7/EVP_SIGNATURE-HMAC.pod b/doc/man7/EVP_SIGNATURE-HMAC.pod
new file mode 100644
index 0000000000..dd74fae88c
--- /dev/null
+++ b/doc/man7/EVP_SIGNATURE-HMAC.pod
@@ -0,0 +1,41 @@
+=pod
+
+=head1 NAME
+
+EVP_SIGNATURE-HMAC, EVP_SIGNATURE-SIPHASH, EVP_SIGNATURE-POLY1305,
+EVP_SIGNATURE-CMAC
+- The legacy B<EVP_PKEY> MAC signature implementations
+
+=head1 DESCRIPTION
+
+The algorithms described here have legacy support for creating MACs using
+L<EVP_DigestSignInit(3)> and related functions. This is not the preferred way of
+creating MACs. Instead you should use the newer L<EVP_MAC_init(3)> functions.
+This mechanism is provided for backwards compatibility with older versions of
+OpenSSL. 
+
+There are no parameters supported by the legacy EVP_PKEY MAC signature
+algorithms. See L<EVP_PKEY-HMAC(7)>, L<EVP_PKEY-SIPHASH(7)>,
+L<EVP_PKEY-POLY1305(7)> or L<EVP_PKEY-CMAC(7)> for details about parameters that
+are supported during the creation of an EVP_PKEY.
+
+=head1 SEE ALSO
+
+L<EVP_MAC_init(3)>,
+L<EVP_DigestSignInit(3)>,
+L<EVP_PKEY-HMAC(7)>,
+L<EVP_PKEY-SIPHASH(7)>,
+L<EVP_PKEY-POLY1305(7)>,
+L<EVP_PKEY-CMAC(7)>,
+L<provider-signature(7)>,
+
+=head1 COPYRIGHT
+
+Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the Apache License 2.0 (the "License").  You may not use
+this file except in compliance with the License.  You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
+=cut