life_cycle-digest.7ossl - Man Page

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)

Referenced By

EVP_DigestInit.3ossl(3), provider-digest.7ossl(7).

2021-09-09 3.0.0 OpenSSL