=pod
=head1 NAME
life_cycle-digest - The digest algorithm life-cycle
=head1 DESCRIPTION
All message digests (MDs) go through a number of stages in their life-cycle:
=over 4
=item start
This state represents the MD before it has been allocated. It is the
starting state for any life-cycle transitions.
=item newed
This state represents the MD after it has been allocated.
=item initialised
This state represents the MD when it is set up and capable of processing
input.
=item updated
This state represents the MD when it is set up and capable of processing
additional input or generating output.
=item 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.
=item 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.
=item freed
This state is entered when the MD is freed. It is the terminal state
for all life-cycle transitions.
=back
=head2 State Transition Diagram
The usual life-cycle of a MD is illustrated:
=begin man
+--------------------+
| 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 | <--------------------+ |
| +------------------+ |
| |
+------------------------------------------------------+
=end man
=for html 
=head2 Formal State Transitions
This section defines all of the legal state transitions.
This is the canonical list.
=begin man
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
=end man
=begin html
| 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_DigestSqueeze |
|
|
|
squeezed |
|
squeezed |
|
|---|
| 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 |
|
|
|
|---|
| EVP_MD_CTX_copy_ex |
|
newed |
initialised |
updated |
|
squeezed |
|
|---|
=end html
=head1 NOTES
At some point the EVP layer will begin enforcing the transitions described
herein.
=head1 SEE ALSO
L, L
=head1 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
L.
=cut