LIFE_CYCLE-CIPHER(7)

NAME
life_cycle-cipher - The cipher algorithm life-cycle

DESCRIPTION
All symmetric ciphers (CIPHERs) go through a number of stages in their life-cycle:

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

newed
    This state represents the CIPHER after it has been allocated.

initialised
    These states represent the CIPHER when it is set up and capable of processing input. There are three possible initialised states:

    initialised using EVP_CipherInit
    initialised for decryption using EVP_DecryptInit
    initialised for encryption using EVP_EncryptInit

updated
    These states represent the CIPHER when it is set up and capable of processing additional input or generating output. The three possible states directly correspond to those for initialised above. The three different streams should not be mixed.

finaled
    This state represents the CIPHER when it has generated output.

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

  State Transition Diagram
The usual life-cycle of a CIPHER is illustrated:
                        +---------------------------+
                        | |
                        | start |
                        | |
                        +---------------------------+ + - - - - - - - - - - - - - +
                        | ' any of the initialised '
                        | EVP_CIPHER_CTX_new ' updated or finaled states '
                        v ' '
                        +---------------------------+ + - - - - - - - - - - - - - +
                        | | |
                        | newed | | EVP_CIPHER_CTX_reset
                        | | <----+
                        +---------------------------+
                        | | |
                        +---------+ | +---------+
          EVP_DecryptInit | | EVP_CipherInit | EVP_EncryptInit
                        v v v
 +---------------------------+ +---------------------------+ +---------------------------+
 | | | | | |
 | initialised | | initialised | | initialised |
 | for decryption | | | | for encryption |
 +---------------------------+ +---------------------------+ +---------------------------+
   | | |
   | EVP_DecryptUpdate | EVP_CipherUpdate EVP_EncryptUpdate |
   | v |
   | +---------------------------+ |
   | | |--------------------+ |
   | | updated | EVP_CipherUpdate | |
   | | | <------------------+ |
   v +---------------------------+ v
 +---------------------------+ | +---------------------------+
 | |---------------------+ | | |
 | updated | EVP_DecryptUpdate | | | updated |------+
 | for decryption | <-------------------+ | | for encryption | |
 +---------------------------+ | +---------------------------+ |
                        | EVP_CipherFinal | | ^ |
                        +-------+ | +--------+ | |
                 EVP_DecryptFinal | | | EVP_EncryptFinal +-------------------+
                        v v v EVP_EncryptUpdate
                        +---------------------------+
                        | |-----------------------------+
                        | finaled | |
                        | | <---------------------------+
                        +---------------------------+ EVP_CIPHER_CTX_get_params
                        | (AEAD encryption)
                        | EVP_CIPHER_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 initialised updated initialised updated freed
                        decryption decryption encryption encryption
 EVP_CIPHER_CTX_new newed
 EVP_CipherInit initialised initialised initialised initialised initialised initialised initialised initialised
 EVP_DecryptInit initialised initialised initialised initialised initialised initialised initialised initialised
                        decryption decryption decryption decryption decryption decryption decryption decryption
 EVP_EncryptInit initialised initialised initialised initialised initialised initialised initialised initialised
                        encryption encryption encryption encryption encryption encryption encryption encryption
 EVP_CipherUpdate updated updated
 EVP_DecryptUpdate updated updated
                        decryption decryption
 EVP_EncryptUpdate updated updated
                        encryption encryption
 EVP_CipherFinal finaled
 EVP_DecryptFinal finaled
 EVP_EncryptFinal finaled
 EVP_CIPHER_CTX_free freed freed freed freed freed freed freed freed freed
 EVP_CIPHER_CTX_reset newed newed newed newed newed newed newed newed
 EVP_CIPHER_CTX_get_params newed initialised updated initialised updated initialised updated
                        decryption decryption encryption encryption
 EVP_CIPHER_CTX_set_params newed initialised updated initialised updated initialised updated
                        decryption decryption encryption encryption
 EVP_CIPHER_CTX_gettable_params newed initialised updated initialised updated initialised updated
                        decryption decryption encryption encryption
 EVP_CIPHER_CTX_settable_params newed initialised updated initialised updated initialised updated
                        decryption decryption encryption encryption

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

SEE ALSO
provider-cipher(7), EVP_EncryptInit(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>.