=pod
=head1 NAME
life_cycle-rand - The RAND algorithm life-cycle
=head1 DESCRIPTION
All random number generator (RANDs)
go through a number of stages in their life-cycle:
=over 4
=item start
This state represents the RAND before it has been allocated. It is the
starting state for any life-cycle transitions.
=item newed
This state represents the RAND after it has been allocated but unable to
generate any output.
=item instantiated
This state represents the RAND when it is set up and capable of generating
output.
=item uninstantiated
This state represents the RAND when it has been shutdown and it is no longer
capable of generating output.
=item freed
This state is entered when the RAND is freed. It is the terminal state
for all life-cycle transitions.
=back
=head2 State Transition Diagram
The usual life-cycle of a RAND is illustrated:
=begin man
+-------------------------+
| start |
+-------------------------+
|
| EVP_RAND_CTX_new
v
+-------------------------+
| newed |
+-------------------------+
|
| EVP_RAND_instantiate
v
EVP_RAND_generate +-------------------------+
+-------------------- | |
| | instantiated |
+-------------------> | | <+
+-------------------------+ '
| '
| EVP_RAND_uninstantiate ' EVP_RAND_instantiate
v '
+-------------------------+ '
| uninstantiated | -+
+-------------------------+
|
| EVP_RAND_CTX_free
v
+-------------------------+
| freed |
+-------------------------+
=end man
=for html <img src="img/rand.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 instantiated uninstantiated freed
EVP_RAND_CTX_new newed
EVP_RAND_instantiate instantiated
EVP_RAND_generate instantiated
EVP_RAND_uninstantiate uninstantiated
EVP_RAND_CTX_free freed freed freed freed
EVP_RAND_CTX_get_params newed instantiated uninstantiated freed
EVP_RAND_CTX_set_params newed instantiated uninstantiated freed
EVP_RAND_CTX_gettable_params newed instantiated uninstantiated freed
EVP_RAND_CTX_settable_params newed instantiated uninstantiated freed
=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="5">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">instantiated</th>
<th style="border:1px solid" align="center">uninstantiated</th>
<th style="border:1px solid" align="center">freed</th></tr>
<tr><th style="border:1px solid" align="left">EVP_RAND_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></tr>
<tr><th style="border:1px solid" align="left">EVP_RAND_instantiate</th>
<td style="border:1px solid" align="center"></td>
<td style="border:1px solid" align="center">instantiated</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_RAND_generate</th>
<td style="border:1px solid" align="center"></td>
<td style="border:1px solid" align="center"></td>
<td style="border:1px solid" align="center">instantiated</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_RAND_uninstantiate</th>
<td style="border:1px solid" align="center"></td>
<td style="border:1px solid" align="center"></td>
<td style="border:1px solid" align="center">uninstantiated</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_RAND_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"></td></tr>
<tr><th style="border:1px solid" align="left">EVP_RAND_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">instantiated</td>
<td style="border:1px solid" align="center">uninstantiated</td>
<td style="border:1px solid" align="center"></td></tr>
<tr><th style="border:1px solid" align="left">EVP_RAND_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">instantiated</td>
<td style="border:1px solid" align="center">uninstantiated</td>
<td style="border:1px solid" align="center"></td></tr>
<tr><th style="border:1px solid" align="left">EVP_RAND_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">instantiated</td>
<td style="border:1px solid" align="center">uninstantiated</td>
<td style="border:1px solid" align="center"></td></tr>
<tr><th style="border:1px solid" align="left">EVP_RAND_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">instantiated</td>
<td style="border:1px solid" align="center">uninstantiated</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-rand(7)>, L<EVP_RAND(3)>.
=head1 HISTORY
The provider RAND 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