LIFE_CYCLE-KDF(7SSL) OpenSSL LIFE_CYCLE-KDF(7SSL)
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>.
3.5.4 2025-09-30 LIFE_CYCLE-KDF(7SSL)
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