LIFE_CYCLE-DIGEST(7ossl)

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. For an XOF digest, this state represents the MD when it has generated a single-shot output.

squeezed
    For an XOF digest, this state represents the MD when it has generated output. It can be called multiple times to generate more output. The output length is variable for each call.

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_reset
                        | EVP_MD_CTX_new +-------------------------------------------------+
                        v v |
              EVP_MD_CTX_reset + - - - - - - - - - - - - - - - - - - - - - - + EVP_MD_CTX_reset |
            +-------------------> ' newed ' <--------------------+ |
            | + - - - - - - - - - - - - - - - - - - - - - - + | |
            | | | |
            | | EVP_DigestInit | |
            | v | |
            | EVP_DigestInit + - - - - - - - - - - - - - - - - - - - - - - + | |
       +----+-------------------> ' initialised ' <+ EVP_DigestInit | |
       | | + - - - - - - - - - - - - - - - - - - - - - - + | | |
       | | | ^ | | |
       | | | EVP_DigestUpdate | EVP_DigestInit | | |
       | | v | | | |
       | | +---------------------------------------------+ | | |
       | +-------------------- | | | | |
       | | | | | |
       | EVP_DigestUpdate | | | | |
       | +-------------------- | | | | |
       | | | updated | | | |
       | +-------------------> | | | | |
       | | | | | |
       | | | | | |
  +----+------------------------- | | -+-------------------+----+ |
  | | +---------------------------------------------+ | | | |
  | | | | | | |
  | | | EVP_DigestSqueeze +-------------------+ | | |
  | | v | | | |
  | | EVP_DigestSqueeze +---------------------------------------------+ | | |
  | | +-------------------- | | | | |
  | | | | squeezed | | | |
  | | +-------------------> | | ---------------------+ | |
  | | +---------------------------------------------+ | |
  | | | | |
  | | +---------------------------------------+ | |
  | | | | |
  | | +---------------------------------------------+ EVP_DigestFinalXOF | | |
  | +------------------------- | finaled | <--------------------+----+ |
  | +---------------------------------------------+ | |
  | EVP_DigestFinal ^ | | | |
  +---------------------------------+ | | EVP_MD_CTX_free | |
                        | v | |
                        | +------------------+ EVP_MD_CTX_free | |
                        | | 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 squeezed freed
 EVP_MD_CTX_new newed
 EVP_DigestInit initialised initialised initialised initialised initialised
 EVP_DigestUpdate updated updated
 EVP_DigestFinal finaled
 EVP_DigestFinalXOF finaled
 EVP_DigestSqueeze squeezed squeezed
 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
 EVP_MD_CTX_copy_ex newed initialised updated squeezed

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

SEE ALSO
provider-digest(7), EVP_DigestInit(3)

COPYRIGHT
Copyright 2021-2023 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>.