doc: life-cycle description for KDFs/PRFs

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14522)

diff --git a/doc/man7/kdf.png b/doc/man7/kdf.png
new file mode 100644 (file)
index 0000000..3a3d153
Binary files /dev/null and b/doc/man7/kdf.png differ

diff --git a/doc/man7/life_cycle-kdf.pod b/doc/man7/life_cycle-kdf.pod
new file mode 100644 (file)
index 0000000..7237c4c
--- /dev/null
+++ b/doc/man7/life_cycle-kdf.pod
@@ -0,0 +1,165 @@
+=pod
+
+=head1 NAME
+
+life_cycle-kdf - The KDF algorithm life-cycle
+
+=head1 DESCRIPTION
+
+All key derivation functions (KDFs) and pseudo random functions (PRFs)
+go through a number of stages in their life-cycle:
+
+=over 4
+
+=item start
+
+This state represents the KDF/PRF before it has been allocated.  It is the
+starting state for any life-cycle transitions.
+
+=item newed
+
+This state represents the KDF/PRF after it has been allocated.
+
+=item deriving
+
+This state represents the KDF/PRF when it is set up and capable of generating
+output.
+
+=item freed
+
+This state is entered when the KDF/PRF is freed.  It is the terminal state
+for all life-cycle transitions.
+
+=back
+
+=head2 State Transition Diagram
+
+The usual life-cycle of a KDF/PRF is illustrated:
+
+=begin man
+
+                     +-------------------+
+                     |       start       |
+                     +-------------------+
+                       |
+                       | EVP_KDF_CTX_new
+                       v
+                     +-------------------+
+                     |       newed       | <+
+                     +-------------------+  |
+                       |                    |
+                       | EVP_KDF_derive     |
+                       v                    | EVP_KDF_CTX_reset
+    EVP_KDF_derive   +-------------------+  |
+  + - - - - - - - -  |                   |  |
+  '                  |     deriving      |  |
+  + - - - - - - - -> |                   | -+
+                     +-------------------+
+                       |
+                       | EVP_KDF_CTX_free
+                       v
+                     +-------------------+
+                     |       freed       |
+                     +-------------------+
+
+=end man
+
+=for html <img src="kdf.png">
+
+=head2 Formal State Transitions
+
+This section defines all of the legal state transitions.
+This is the canonical list.
+
+=begin man
+
+ Function Call                   ------------- Current State -------------
+                                 start       newed       deriving    freed
+ EVP_KDF_CTX_new                 newed           
+ EVP_KDF_derive                             deriving     deriving
+ EVP_KDF_CTX_free                freed       freed        freed
+ EVP_KDF_CTX_reset                           newed        newed
+ EVP_KDF_CTX_get_params                      newed       deriving
+ EVP_KDF_CTX_set_params                      newed       deriving
+ EVP_KDF_CTX_gettable_params                 newed       deriving
+ EVP_KDF_CTX_settable_params                 newed       deriving
+
+=end man
+
+=begin html
+
+<table style="border:1px solid; border-collapse:collapse">
+<tr><th style="border:1px solid" align="left">Function Call</th>
+    <th style="border:1px solid" colspan="4">Current State</th></tr>
+<tr><th style="border:1px solid"></th>
+    <th style="border:1px solid" align="center">start</th>
+    <th style="border:1px solid" align="center">newed</th>
+    <th style="border:1px solid" align="center">deriving</th>
+    <th style="border:1px solid" align="center">freed</th></tr>
+<tr><th style="border:1px solid" align="left">EVP_KDF_CTX_new</th>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid"></td>
+    <td style="border:1px solid"></td>
+    <td style="border:1px solid"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_KDF_derive</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">deriving</td>
+    <td style="border:1px solid"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_KDF_CTX_free</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">deriving</td>
+    <td style="border:1px solid"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_KDF_CTX_reset</th>
+    <td style="border:1px solid" align="center">freed</td>
+    <td style="border:1px solid" align="center">freed</td>
+    <td style="border:1px solid" align="center">freed</td>
+    <td style="border:1px solid"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_KDF_CTX_get_params</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">deriving</td>
+    <td style="border:1px solid"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_KDF_CTX_set_params</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">deriving</td>
+    <td style="border:1px solid"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_KDF_CTX_gettable_params</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">deriving</td>
+    <td style="border:1px solid"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_KDF_CTX_settable_params</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">deriving</td>
+    <td style="border:1px solid"></td></tr>
+</table>
+
+=end html
+
+=head1 NOTES
+
+At some point the EVP layer will begin enforcing the transitions described
+herein.
+
+=head1 SEE ALSO
+
+L<provider-kdf(7)>, L<EVP_KDF(3)>.
+
+=head1 HISTORY
+
+The provider KDF interface was introduced in OpenSSL 3.0.
+
+=head1 COPYRIGHT
+
+Copyright 2021 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