NAME

       life_cycle-kdf - The KDF algorithm life-cycle

DESCRIPTION

       All key derivation functions (KDFs) and pseudo random functions (PRFs) go through a number
       of stages in their life-cycle:

       start
           This state represents the KDF/PRF before it has been allocated.  It is the starting
           state for any life-cycle transitions.

       newed
           This state represents the KDF/PRF after it has been allocated.

       deriving
           This state represents the KDF/PRF when it is set up and capable of generating output.

       freed
           This state is entered when the KDF/PRF is freed.  It is the terminal state for all
           life-cycle transitions.

   State Transition Diagram
       The usual life-cycle of a KDF/PRF is illustrated:
                            +-------------------+
                            |       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       |
                            +-------------------+

   Formal State Transitions
       This section defines all of the legal state transitions.  This is the canonical list.
        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

NOTES

       At some point the EVP layer will begin enforcing the transitions described herein.

SEE ALSO

       provider-kdf(7), EVP_KDF(3).

HISTORY

       The provider KDF interface was introduced in OpenSSL 3.0.

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 <https://www.openssl.org/source/license.html>.