LIFE_CYCLE-KDF(7) | OpenSSL | LIFE_CYCLE-KDF(7)

# 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>.

2026-06-09 | 3.5.7