LIFE_CYCLE-DIGEST(7)

LIFE_CYCLE-DIGEST(7) | OpenSSL | LIFE_CYCLE-DIGEST(7)

# 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>.

2026-04-07 | 3.5.6