doc: add cipher life cycle documentation

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15637)

diff --git a/doc/man7/img/cipher.png b/doc/man7/img/cipher.png
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diff --git a/doc/man7/life_cycle-cipher.pod b/doc/man7/life_cycle-cipher.pod
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+=pod
+
+=head1 NAME
+
+life_cycle-cipher - The cipher algorithm life-cycle
+
+=head1 DESCRIPTION
+
+All symmetric ciphers (CIPHERs) go through a number of stages in their
+life-cycle:
+
+=over 4
+
+=item start
+
+This state represents the CIPHER before it has been allocated.  It is the
+starting state for any life-cycle transitions.
+
+=item newed
+
+This state represents the CIPHER after it has been allocated.
+
+=item initialised
+
+These states represent the CIPHER when it is set up and capable of processing
+input.  There are three possible initialised states:
+
+=over 4
+
+=item initialised using EVP_CipherInit
+
+=item initialised for decryption using EVP_DecryptInit
+
+=item initialised for encryption using EVP_EncryptInit
+
+=back
+
+=item updated
+
+These states represent the CIPHER when it is set up and capable of processing
+additional input or generating output.  The three possible states directly
+correspond to those for initialised above.  The three different streams should
+not be mixed.
+
+=item finaled
+
+This state represents the CIPHER when it has generated output.
+
+=item freed
+
+This state is entered when the CIPHER is freed.  It is the terminal state
+for all life-cycle transitions.
+
+=back
+
+=head2 State Transition Diagram
+
+The usual life-cycle of a CIPHER is illustrated:
+
+=begin man
+
+                                 +---------------------------+
+                                 |                           |
+                                 |           start           |
+                                 |                           |
+                                 +---------------------------+   + - - - - - - - - - - - - - +
+                                       |                         '  any of the initialised   '
+                                       | EVP_CIPHER_CTX_new      ' updated or finaled states '
+                                       v                         '                           '
+                                 +---------------------------+   + - - - - - - - - - - - - - +
+                                 |                           |      |
+                                 |           newed           |      | EVP_CIPHER_CTX_reset
+                                 |                           | <----+
+                                 +---------------------------+
+                                    |   |                 |
+                          +---------+   |                 +---------+
+          EVP_DecryptInit |             | EVP_CipherInit            | EVP_EncryptInit
+                          v             v                           v
+ +---------------------------+   +---------------------------+   +---------------------------+
+ |                           |   |                           |   |                           |
+ |        initialised        |   |        initialised        |   |        initialised        |
+ |       for decryption      |   |                           |   |       for encryption      |
+ +---------------------------+   +---------------------------+   +---------------------------+
+   |                                   |                                                   |
+   | EVP_DecryptUpdate                 | EVP_CipherUpdate                EVP_EncryptUpdate |
+   |                                   v                                                   |
+   |                             +---------------------------+                             |
+   |                             |                           |--------------------+        |
+   |                             |          updated          |   EVP_CipherUpdate |        |
+   |                             |                           | <------------------+        |
+   v                             +---------------------------+                             v
+ +---------------------------+                         |         +---------------------------+
+ |                           |---------------------+   |         |                           |
+ |          updated          |   EVP_DecryptUpdate |   |         |          updated          |------+
+ |       for decryption      | <-------------------+   |         |       for encryption      |      |
+ +---------------------------+                         |         +---------------------------+      |
+                          |            EVP_CipherFinal |            |           ^                   |
+                          +-------+                    |   +--------+           |                   |
+                 EVP_DecryptFinal |                    |   | EVP_EncryptFinal   +-------------------+
+                                  v                    v   v                      EVP_EncryptUpdate
+                                 +---------------------------+
+                                 |                           |-----------------------------+
+                                 |          finaled          |                             |
+                                 |                           | <---------------------------+
+                                 +---------------------------+   EVP_CIPHER_CTX_get_params
+                                       |                             (AEAD encryption)
+                                       | EVP_CIPHER_CTX_free
+                                       v
+                                 +---------------------------+
+                                 |                           |
+                                 |           freed           |
+                                 |                           |
+                                 +---------------------------+
+
+=end man
+
+=for html <img src="img/cipher.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    initialised   updated     finaled   initialised   updated    initialised   updated    freed
+                                                                                    decryption  decryption   encryption  encryption
+ EVP_CIPHER_CTX_new           newed           
+ EVP_CipherInit                    initialised initialised initialised initialised initialised initialised  initialised initialised
+ EVP_DecryptInit                   initialised initialised initialised initialised initialised initialised  initialised initialised
+                                    decryption  decryption  decryption  decryption  decryption  decryption  decryption  decryption  
+ EVP_EncryptInit                   initialised initialised initialised initialised initialised initialised  initialised initialised
+                                    encryption  encryption  encryption  encryption  encryption  encryption  encryption  encryption  
+ EVP_CipherUpdate                                updated     updated
+ EVP_DecryptUpdate                                                                   updated     updated
+                                                                                    decryption  decryption
+ EVP_EncryptUpdate                                                                                            updated     updated
+                                                                                                             encryption  encryption
+ EVP_CipherFinal                                             finaled
+ EVP_DecryptFinal                                                                                finaled
+ EVP_EncryptFinal                                                                                                         finaled
+ EVP_CIPHER_CTX_free          freed   freed       freed       freed       freed       freed       freed        freed       freed
+ EVP_CIPHER_CTX_reset                 newed       newed       newed       newed       newed       newed        newed       newed
+ EVP_CIPHER_CTX_get_params            newed    initialised   updated               initialised   updated    initialised   updated
+                                                                                    decryption  decryption   encryption  encryption
+ EVP_CIPHER_CTX_set_params            newed    initialised   updated               initialised   updated    initialised   updated
+                                                                                    decryption  decryption   encryption  encryption
+ EVP_CIPHER_CTX_gettable_params       newed    initialised   updated               initialised   updated    initialised   updated
+                                                                                    decryption  decryption   encryption  encryption
+ EVP_CIPHER_CTX_settable_params       newed    initialised   updated               initialised   updated    initialised   updated
+                                                                                    decryption  decryption   encryption  encryption
+
+=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="10">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">initialised</th>
+    <th style="border:1px solid" align="center">updated</th>
+    <th style="border:1px solid" align="center">finaled</th>
+    <th style="border:1px solid" align="center">initialised<br>decryption</th>
+    <th style="border:1px solid" align="center">updated<br>decryption</th>
+    <th style="border:1px solid" align="center">initialised<br>encryption</th>
+    <th style="border:1px solid" align="center">updated<br>encryption</th>
+    <th style="border:1px solid" align="center">freed</th></tr>
+<tr><th style="border:1px solid" align="left">EVP_CIPHER_CTX_new</th>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_CipherInit</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">initialised</td>
+    <td style="border:1px solid" align="center">initialised</td>
+    <td style="border:1px solid" align="center">initialised</td>
+    <td style="border:1px solid" align="center">initialised</td>
+    <td style="border:1px solid" align="center">initialised</td>
+    <td style="border:1px solid" align="center">initialised</td>
+    <td style="border:1px solid" align="center">initialised</td>
+    <td style="border:1px solid" align="center">initialised</td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_DecryptInit</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_EncryptInit</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_CipherUpdate</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">updated</td>
+    <td style="border:1px solid" align="center">updated</td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_DecryptUpdate</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">updated<br>decryption</td>
+    <td style="border:1px solid" align="center">updated<br>decryption</td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_EncryptUpdate</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">updated<br>encryption</td>
+    <td style="border:1px solid" align="center">updated<br>encryption</td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_CipherFinal</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">finaled</td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_DecryptFinal</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">finaled<br>decryption</td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_EncryptFinal</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">finaled<br>decryption</td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_CIPHER_CTX_free</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" 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" 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" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_CIPHER_CTX_reset</th>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center">newed</td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_CIPHER_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">initialised</td>
+    <td style="border:1px solid" align="center">updated</td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">updated<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">updated<br>encryption</td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_CIPHER_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">initialised</td>
+    <td style="border:1px solid" align="center">updated</td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">updated<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">updated<br>encryption</td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_CIPHER_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">initialised</td>
+    <td style="border:1px solid" align="center">updated</td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">updated<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">updated<br>encryption</td>
+    <td style="border:1px solid" align="center"></td></tr>
+<tr><th style="border:1px solid" align="left">EVP_CIPHER_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">initialised</td>
+    <td style="border:1px solid" align="center">updated</td>
+    <td style="border:1px solid" align="center"></td>
+    <td style="border:1px solid" align="center">initialised<br>decryption</td>
+    <td style="border:1px solid" align="center">updated<br>decryption</td>
+    <td style="border:1px solid" align="center">initialised<br>encryption</td>
+    <td style="border:1px solid" align="center">updated<br>encryption</td>
+    <td style="border:1px solid" align="center"></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-cipher(7)>, L<EVP_EncryptInit(3)>
+
+=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