life_cycle-kdf - The KDF algorithm life-cycle

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3.5.0                                              2025-06-04                               LIFE_CYCLE-KDF(7SSL)

       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.

   StateTransitionDiagram
       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       |
                            +-------------------+

   FormalStateTransitions
       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

       The provider KDF interface was introduced in OpenSSL 3.0.

       life_cycle-kdf - The KDF algorithm life-cycle

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

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