life_cycle-digest

NAME

life_cycle-digest - The digest algorithm life-cycle

DESCRIPTION

All message digests (MDs) go through a number of stages in their life-cycle:

start

This state represents the MD before it has been allocated. It is the starting state for any life-cycle transitions.

newed

This state represents the MD after it has been allocated.

initialised

This state represents the MD when it is set up and capable of processing input.

updated

This state represents the MD when it is set up and capable of processing additional input or generating output.

finaled

This state represents the MD when it has generated output.

freed

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

State Transition Diagram

The usual life-cycle of a MD is illustrated:
+-------------------+
| start |
+-------------------+
|
| EVP_MD_CTX_new
v
+-------------------+ EVP_MD_CTX_reset
| newed | <------------------------------+
+-------------------+ |
| |
| EVP_DigestInit |
v |
+-------------------+ |
+--> | initialised | <+ EVP_DigestInit |
| +-------------------+ | |
| | | EVP_DigestUpdate |
| | EVP_DigestUpdate | +------------------+ |
| v | v | |
| +------------------------------------------------+ |
EVP_DigestInit | | updated | --+
| +------------------------------------------------+ |
| | | |
| | EVP_DigestFinal | EVP_DigestFinalXOF |
| v v |
| +------------------------------------------------+ |
+--- | finaled | --+
+------------------------------------------------+
|
| EVP_MD_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 initialised updated finaled freed
EVP_MD_CTX_new newed
EVP_DigestInit initialised initialised initialised initialised
EVP_DigestUpdate updated updated
EVP_DigestFinal finaled
EVP_DigestFinalXOF finaled
EVP_MD_CTX_free freed freed freed freed freed
EVP_MD_CTX_reset newed newed newed newed
EVP_MD_CTX_get_params newed initialised updated
EVP_MD_CTX_set_params newed initialised updated
EVP_MD_CTX_gettable_params newed initialised updated
EVP_MD_CTX_settable_params newed initialised updated

NOTES

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

SEE ALSO

provider-digest(7), EVP_DigestInit(3)

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>.