ENGINE_get_DH, ENGINE_get_DSA, ENGINE_by_id, ENGINE_get_cipher_engine,
ENGINE_get_default_DH, ENGINE_get_default_DSA, ENGINE_get_default_RAND,
ENGINE_get_default_RSA, ENGINE_get_digest_engine, ENGINE_get_first,
ENGINE_get_last, ENGINE_get_next, ENGINE_get_prev, ENGINE_new,
ENGINE_get_ciphers, ENGINE_get_ctrl_function, ENGINE_get_digests,
ENGINE_get_destroy_function, ENGINE_get_finish_function,
ENGINE_get_init_function, ENGINE_get_load_privkey_function,
ENGINE_get_load_pubkey_function, ENGINE_load_private_key,
ENGINE_load_public_key, ENGINE_get_RAND, ENGINE_get_RSA, ENGINE_get_id,
ENGINE_get_name, ENGINE_get_cmd_defns, ENGINE_get_cipher, ENGINE_get_digest,
ENGINE_add, ENGINE_cmd_is_executable, ENGINE_ctrl, ENGINE_ctrl_cmd,
ENGINE_ctrl_cmd_string, ENGINE_finish, ENGINE_free, ENGINE_get_flags,
ENGINE_init, ENGINE_register_DH, ENGINE_register_DSA, ENGINE_register_RAND,
ENGINE_register_RSA, ENGINE_register_all_complete, ENGINE_register_ciphers,
ENGINE_register_complete, ENGINE_register_digests, ENGINE_remove,
ENGINE_set_DH, ENGINE_set_DSA, ENGINE_set_RAND, ENGINE_set_RSA,
ENGINE_set_ciphers, ENGINE_set_cmd_defns, ENGINE_set_ctrl_function,
ENGINE_set_default, ENGINE_set_default_DH, ENGINE_set_default_DSA,
ENGINE_set_default_RAND, ENGINE_set_default_RSA, ENGINE_set_default_ciphers,
ENGINE_set_default_digests, ENGINE_set_default_string,
ENGINE_set_destroy_function, ENGINE_set_digests, ENGINE_set_finish_function,
ENGINE_set_flags, ENGINE_set_id, ENGINE_set_init_function,
ENGINE_set_load_privkey_function, ENGINE_set_load_pubkey_function,
ENGINE_set_name, ENGINE_up_ref, ENGINE_get_table_flags, ENGINE_cleanup,
ENGINE_load_builtin_engines, ENGINE_register_all_DH, ENGINE_register_all_DSA,
ENGINE_register_all_RAND, ENGINE_register_all_RSA,
ENGINE_register_all_ciphers, ENGINE_register_all_digests,
ENGINE_set_table_flags, ENGINE_unregister_DH, ENGINE_unregister_DSA,
ENGINE_unregister_RAND, ENGINE_unregister_RSA, ENGINE_unregister_ciphers,
ENGINE_unregister_digests - ENGINE cryptographic module support
#include <openssl/engine.h>
The following functions have been deprecated since OpenSSL 3.0, and can be
hidden entirely by defining
OPENSSL_API_COMPAT with a suitable version
value, see
openssl_user_macros(7):
ENGINE *ENGINE_get_first(void);
ENGINE *ENGINE_get_last(void);
ENGINE *ENGINE_get_next(ENGINE *e);
ENGINE *ENGINE_get_prev(ENGINE *e);
int ENGINE_add(ENGINE *e);
int ENGINE_remove(ENGINE *e);
ENGINE *ENGINE_by_id(const char *id);
int ENGINE_init(ENGINE *e);
int ENGINE_finish(ENGINE *e);
void ENGINE_load_builtin_engines(void);
ENGINE *ENGINE_get_default_RSA(void);
ENGINE *ENGINE_get_default_DSA(void);
ENGINE *ENGINE_get_default_DH(void);
ENGINE *ENGINE_get_default_RAND(void);
ENGINE *ENGINE_get_cipher_engine(int nid);
ENGINE *ENGINE_get_digest_engine(int nid);
int ENGINE_set_default_RSA(ENGINE *e);
int ENGINE_set_default_DSA(ENGINE *e);
int ENGINE_set_default_DH(ENGINE *e);
int ENGINE_set_default_RAND(ENGINE *e);
int ENGINE_set_default_ciphers(ENGINE *e);
int ENGINE_set_default_digests(ENGINE *e);
int ENGINE_set_default_string(ENGINE *e, const char *list);
int ENGINE_set_default(ENGINE *e, unsigned int flags);
unsigned int ENGINE_get_table_flags(void);
void ENGINE_set_table_flags(unsigned int flags);
int ENGINE_register_RSA(ENGINE *e);
void ENGINE_unregister_RSA(ENGINE *e);
void ENGINE_register_all_RSA(void);
int ENGINE_register_DSA(ENGINE *e);
void ENGINE_unregister_DSA(ENGINE *e);
void ENGINE_register_all_DSA(void);
int ENGINE_register_DH(ENGINE *e);
void ENGINE_unregister_DH(ENGINE *e);
void ENGINE_register_all_DH(void);
int ENGINE_register_RAND(ENGINE *e);
void ENGINE_unregister_RAND(ENGINE *e);
void ENGINE_register_all_RAND(void);
int ENGINE_register_ciphers(ENGINE *e);
void ENGINE_unregister_ciphers(ENGINE *e);
void ENGINE_register_all_ciphers(void);
int ENGINE_register_digests(ENGINE *e);
void ENGINE_unregister_digests(ENGINE *e);
void ENGINE_register_all_digests(void);
int ENGINE_register_complete(ENGINE *e);
int ENGINE_register_all_complete(void);
int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void));
int ENGINE_cmd_is_executable(ENGINE *e, int cmd);
int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name,
long i, void *p, void (*f)(void), int cmd_optional);
int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg,
int cmd_optional);
ENGINE *ENGINE_new(void);
int ENGINE_free(ENGINE *e);
int ENGINE_up_ref(ENGINE *e);
int ENGINE_set_id(ENGINE *e, const char *id);
int ENGINE_set_name(ENGINE *e, const char *name);
int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth);
int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth);
int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth);
int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth);
int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f);
int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f);
int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f);
int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f);
int ENGINE_set_load_privkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpriv_f);
int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f);
int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f);
int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f);
int ENGINE_set_flags(ENGINE *e, int flags);
int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns);
const char *ENGINE_get_id(const ENGINE *e);
const char *ENGINE_get_name(const ENGINE *e);
const RSA_METHOD *ENGINE_get_RSA(const ENGINE *e);
const DSA_METHOD *ENGINE_get_DSA(const ENGINE *e);
const DH_METHOD *ENGINE_get_DH(const ENGINE *e);
const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e);
ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e);
ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e);
ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e);
ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e);
ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e);
ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e);
ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e);
ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e);
const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid);
const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid);
int ENGINE_get_flags(const ENGINE *e);
const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e);
EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char *key_id,
UI_METHOD *ui_method, void *callback_data);
EVP_PKEY *ENGINE_load_public_key(ENGINE *e, const char *key_id,
UI_METHOD *ui_method, void *callback_data);
The following function has been deprecated since OpenSSL 1.1.0, and can be
hidden entirely by defining
OPENSSL_API_COMPAT with a suitable version
value, see
openssl_user_macros(7):
void ENGINE_cleanup(void);
All of the functions described on this page are deprecated. Applications should
instead use the provider APIs.
These functions create, manipulate, and use cryptographic modules in the form of
ENGINE objects. These objects act as containers for implementations of
cryptographic algorithms, and support a reference-counted mechanism to allow
them to be dynamically loaded in and out of the running application.
The cryptographic functionality that can be provided by an
ENGINE
implementation includes the following abstractions;
RSA_METHOD - for providing alternative RSA implementations
DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD,
- similarly for other OpenSSL APIs
EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid')
EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid')
key-loading - loading public and/or private EVP_PKEY keys
Due to the modular nature of the ENGINE API, pointers to ENGINEs need to be
treated as handles - i.e. not only as pointers, but also as references to the
underlying ENGINE object. Ie. one should obtain a new reference when making
copies of an ENGINE pointer if the copies will be used (and released)
independently.
ENGINE objects have two levels of reference-counting to match the way in which
the objects are used. At the most basic level, each ENGINE pointer is
inherently a
structural reference - a structural reference is required
to use the pointer value at all, as this kind of reference is a guarantee that
the structure can not be deallocated until the reference is released.
However, a structural reference provides no guarantee that the ENGINE is
initialised and able to use any of its cryptographic implementations. Indeed
it's quite possible that most ENGINEs will not initialise at all in typical
environments, as ENGINEs are typically used to support specialised hardware.
To use an ENGINE's functionality, you need a
functional reference. This
kind of reference can be considered a specialised form of structural
reference, because each functional reference implicitly contains a structural
reference as well - however to avoid difficult-to-find programming bugs, it is
recommended to treat the two kinds of reference independently. If you have a
functional reference to an ENGINE, you have a guarantee that the ENGINE has
been initialised and is ready to perform cryptographic operations, and will
remain initialised until after you have released your reference.
Structural references
This basic type of reference is used for instantiating new ENGINEs, iterating
across OpenSSL's internal linked-list of loaded ENGINEs, reading information
about an ENGINE, etc. Essentially a structural reference is sufficient if you
only need to query or manipulate the data of an ENGINE implementation rather
than use its functionality.
The
ENGINE_new() function returns a structural reference to a new (empty)
ENGINE object. There are other ENGINE API functions that return structural
references such as;
ENGINE_by_id(),
ENGINE_get_first(),
ENGINE_get_last(),
ENGINE_get_next(),
ENGINE_get_prev().
All structural references should be released by a corresponding to call to the
ENGINE_free() function - the ENGINE object itself will only actually be
cleaned up and deallocated when the last structural reference is released.
It should also be noted that many ENGINE API function calls that accept a
structural reference will internally obtain another reference - typically this
happens whenever the supplied ENGINE will be needed by OpenSSL after the
function has returned. Eg. the function to add a new ENGINE to OpenSSL's
internal list is
ENGINE_add() - if this function returns success, then
OpenSSL will have stored a new structural reference internally so the caller
is still responsible for freeing their own reference with
ENGINE_free()
when they are finished with it. In a similar way, some functions will
automatically release the structural reference passed to it if part of the
function's job is to do so. Eg. the
ENGINE_get_next() and
ENGINE_get_prev() functions are used for iterating across the internal
ENGINE list - they will return a new structural reference to the next (or
previous) ENGINE in the list or NULL if at the end (or beginning) of the list,
but in either case the structural reference passed to the function is released
on behalf of the caller.
To clarify a particular function's handling of references, one should always
consult that function's documentation "man" page, or failing that
the
<openssl/engine.h> header file includes some hints.
Functional references
As mentioned, functional references exist when the cryptographic functionality
of an ENGINE is required to be available. A functional reference can be
obtained in one of two ways; from an existing structural reference to the
required ENGINE, or by asking OpenSSL for the default operational ENGINE for a
given cryptographic purpose.
To obtain a functional reference from an existing structural reference, call the
ENGINE_init() function. This returns zero if the ENGINE was not already
operational and couldn't be successfully initialised (e.g. lack of system
drivers, no special hardware attached, etc), otherwise it will return nonzero
to indicate that the ENGINE is now operational and will have allocated a new
functional reference to the ENGINE. All functional references are
released by calling
ENGINE_finish() (which removes the implicit
structural reference as well).
The second way to get a functional reference is by asking OpenSSL for a default
implementation for a given task, e.g. by
ENGINE_get_default_RSA(),
ENGINE_get_default_cipher_engine(), etc. These are discussed in the
next section, though they are not usually required by application programmers
as they are used automatically when creating and using the relevant
algorithm-specific types in OpenSSL, such as RSA, DSA, EVP_CIPHER_CTX, etc.
For each supported abstraction, the ENGINE code maintains an internal table of
state to control which implementations are available for a given abstraction
and which should be used by default. These implementations are registered in
the tables and indexed by an 'nid' value, because abstractions like EVP_CIPHER
and EVP_DIGEST support many distinct algorithms and modes, and ENGINEs can
support arbitrarily many of them. In the case of other abstractions like RSA,
DSA, etc, there is only one "algorithm" so all implementations
implicitly register using the same 'nid' index.
When a default ENGINE is requested for a given abstraction/algorithm/mode, (e.g.
when calling RSA_new_method(NULL)), a "get_default" call will be
made to the ENGINE subsystem to process the corresponding state table and
return a functional reference to an initialised ENGINE whose implementation
should be used. If no ENGINE should (or can) be used, it will return NULL and
the caller will operate with a NULL ENGINE handle - this usually equates to
using the conventional software implementation. In the latter case, OpenSSL
will from then on behave the way it used to before the ENGINE API existed.
Each state table has a flag to note whether it has processed this
"get_default" query since the table was last modified, because to
process this question it must iterate across all the registered ENGINEs in the
table trying to initialise each of them in turn, in case one of them is
operational. If it returns a functional reference to an ENGINE, it will also
cache another reference to speed up processing future queries (without needing
to iterate across the table). Likewise, it will cache a NULL response if no
ENGINE was available so that future queries won't repeat the same iteration
unless the state table changes. This behaviour can also be changed; if the
ENGINE_TABLE_FLAG_NOINIT flag is set (using
ENGINE_set_table_flags()),
no attempted initialisations will take place, instead the only way for the
state table to return a non-NULL ENGINE to the "get_default" query
will be if one is expressly set in the table. Eg.
ENGINE_set_default_RSA() does the same job as
ENGINE_register_RSA() except that it also sets the state table's cached
response for the "get_default" query. In the case of abstractions
like EVP_CIPHER, where implementations are indexed by 'nid', these flags and
cached-responses are distinct for each 'nid' value.
This section will explain the basic things an application programmer should
support to make the most useful elements of the ENGINE functionality available
to the user. The first thing to consider is whether the programmer wishes to
make alternative ENGINE modules available to the application and user. OpenSSL
maintains an internal linked list of "visible" ENGINEs from which it
has to operate - at start-up, this list is empty and in fact if an application
does not call any ENGINE API calls and it uses static linking against openssl,
then the resulting application binary will not contain any alternative ENGINE
code at all. So the first consideration is whether any/all available ENGINE
implementations should be made visible to OpenSSL - this is controlled by
calling the various "load" functions.
The fact that ENGINEs are made visible to OpenSSL (and thus are linked into the
program and loaded into memory at run-time) does not mean they are
"registered" or called into use by OpenSSL automatically - that
behaviour is something for the application to control. Some applications will
want to allow the user to specify exactly which ENGINE they want used if any
is to be used at all. Others may prefer to load all support and have OpenSSL
automatically use at run-time any ENGINE that is able to successfully
initialise - i.e. to assume that this corresponds to acceleration hardware
attached to the machine or some such thing. There are probably numerous other
ways in which applications may prefer to handle things, so we will simply
illustrate the consequences as they apply to a couple of simple cases and
leave developers to consider these and the source code to openssl's built-in
utilities as guides.
If no ENGINE API functions are called within an application, then OpenSSL will
not allocate any internal resources. Prior to OpenSSL 1.1.0, however, if any
ENGINEs are loaded, even if not registered or used, it was necessary to call
ENGINE_cleanup() before the program exits.
Using a specific ENGINE implementation
Here we'll assume an application has been configured by its user or admin to
want to use the "ACME" ENGINE if it is available in the version of
OpenSSL the application was compiled with. If it is available, it should be
used by default for all RSA, DSA, and symmetric cipher operations, otherwise
OpenSSL should use its built-in software as per usual. The following code
illustrates how to approach this;
ENGINE *e;
const char *engine_id = "ACME";
ENGINE_load_builtin_engines();
e = ENGINE_by_id(engine_id);
if (!e)
/* the engine isn't available */
return;
if (!ENGINE_init(e)) {
/* the engine couldn't initialise, release 'e' */
ENGINE_free(e);
return;
}
if (!ENGINE_set_default_RSA(e))
/*
* This should only happen when 'e' can't initialise, but the previous
* statement suggests it did.
*/
abort();
ENGINE_set_default_DSA(e);
ENGINE_set_default_ciphers(e);
/* Release the functional reference from ENGINE_init() */
ENGINE_finish(e);
/* Release the structural reference from ENGINE_by_id() */
ENGINE_free(e);
Automatically using built-in ENGINE implementations
Here we'll assume we want to load and register all ENGINE implementations
bundled with OpenSSL, such that for any cryptographic algorithm required by
OpenSSL - if there is an ENGINE that implements it and can be initialised, it
should be used. The following code illustrates how this can work;
/* Load all bundled ENGINEs into memory and make them visible */
ENGINE_load_builtin_engines();
/* Register all of them for every algorithm they collectively implement */
ENGINE_register_all_complete();
That's all that's required. Eg. the next time OpenSSL tries to set up an RSA
key, any bundled ENGINEs that implement RSA_METHOD will be passed to
ENGINE_init() and if any of those succeed, that ENGINE will be set as
the default for RSA use from then on.
There is a mechanism supported by the ENGINE framework that allows each ENGINE
implementation to define an arbitrary set of configuration
"commands" and expose them to OpenSSL and any applications based on
OpenSSL. This mechanism is entirely based on the use of name-value pairs and
assumes ASCII input (no unicode or UTF for now!), so it is ideal if
applications want to provide a transparent way for users to provide arbitrary
configuration "directives" directly to such ENGINEs. It is also
possible for the application to dynamically interrogate the loaded ENGINE
implementations for the names, descriptions, and input flags of their
available "control commands", providing a more flexible
configuration scheme. However, if the user is expected to know which ENGINE
device he/she is using (in the case of specialised hardware, this goes without
saying) then applications may not need to concern themselves with discovering
the supported control commands and simply prefer to pass settings into ENGINEs
exactly as they are provided by the user.
Before illustrating how control commands work, it is worth mentioning what they
are typically used for. Broadly speaking there are two uses for control
commands; the first is to provide the necessary details to the implementation
(which may know nothing at all specific to the host system) so that it can be
initialised for use. This could include the path to any driver or config files
it needs to load, required network addresses, smart-card identifiers,
passwords to initialise protected devices, logging information, etc etc. This
class of commands typically needs to be passed to an ENGINE
before
attempting to initialise it, i.e. before calling
ENGINE_init(). The
other class of commands consist of settings or operations that tweak certain
behaviour or cause certain operations to take place, and these commands may
work either before or after
ENGINE_init(), or in some cases both.
ENGINE implementations should provide indications of this in the descriptions
attached to built-in control commands and/or in external product
documentation.
Issuing control commands to an ENGINE
Let's illustrate by example; a function for which the caller supplies the name
of the ENGINE it wishes to use, a table of string-pairs for use before
initialisation, and another table for use after initialisation. Note that the
string-pairs used for control commands consist of a command "name"
followed by the command "parameter" - the parameter could be NULL in
some cases but the name can not. This function should initialise the ENGINE
(issuing the "pre" commands beforehand and the "post"
commands afterwards) and set it as the default for everything except RAND and
then return a boolean success or failure.
int generic_load_engine_fn(const char *engine_id,
const char **pre_cmds, int pre_num,
const char **post_cmds, int post_num)
{
ENGINE *e = ENGINE_by_id(engine_id);
if (!e) return 0;
while (pre_num--) {
if (!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) {
fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)");
ENGINE_free(e);
return 0;
}
pre_cmds += 2;
}
if (!ENGINE_init(e)) {
fprintf(stderr, "Failed initialisation\n");
ENGINE_free(e);
return 0;
}
/*
* ENGINE_init() returned a functional reference, so free the structural
* reference from ENGINE_by_id().
*/
ENGINE_free(e);
while (post_num--) {
if (!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) {
fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)");
ENGINE_finish(e);
return 0;
}
post_cmds += 2;
}
ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND);
/* Success */
return 1;
}
Note that
ENGINE_ctrl_cmd_string() accepts a boolean argument that can
relax the semantics of the function - if set nonzero it will only return
failure if the ENGINE supported the given command name but failed while
executing it, if the ENGINE doesn't support the command name it will simply
return success without doing anything. In this case we assume the user is only
supplying commands specific to the given ENGINE so we set this to FALSE.
Discovering supported control commands
It is possible to discover at run-time the names, numerical-ids, descriptions
and input parameters of the control commands supported by an ENGINE using a
structural reference. Note that some control commands are defined by OpenSSL
itself and it will intercept and handle these control commands on behalf of
the ENGINE, i.e. the ENGINE's
ctrl() handler is not used for the
control command.
<openssl/engine.h> defines an index,
ENGINE_CMD_BASE, that all control commands implemented by ENGINEs should be
numbered from. Any command value lower than this symbol is considered a
"generic" command is handled directly by the OpenSSL core routines.
It is using these "core" control commands that one can discover the
control commands implemented by a given ENGINE, specifically the commands:
ENGINE_HAS_CTRL_FUNCTION
ENGINE_CTRL_GET_FIRST_CMD_TYPE
ENGINE_CTRL_GET_NEXT_CMD_TYPE
ENGINE_CTRL_GET_CMD_FROM_NAME
ENGINE_CTRL_GET_NAME_LEN_FROM_CMD
ENGINE_CTRL_GET_NAME_FROM_CMD
ENGINE_CTRL_GET_DESC_LEN_FROM_CMD
ENGINE_CTRL_GET_DESC_FROM_CMD
ENGINE_CTRL_GET_CMD_FLAGS
Whilst these commands are automatically processed by the OpenSSL framework code,
they use various properties exposed by each ENGINE to process these queries.
An ENGINE has 3 properties it exposes that can affect how this behaves; it can
supply a
ctrl() handler, it can specify ENGINE_FLAGS_MANUAL_CMD_CTRL in
the ENGINE's flags, and it can expose an array of control command
descriptions. If an ENGINE specifies the ENGINE_FLAGS_MANUAL_CMD_CTRL flag,
then it will simply pass all these "core" control commands directly
to the ENGINE's
ctrl() handler (and thus, it must have supplied one),
so it is up to the ENGINE to reply to these "discovery" commands
itself. If that flag is not set, then the OpenSSL framework code will work
with the following rules:
if no ctrl() handler supplied;
ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero),
all other commands fail.
if a ctrl() handler was supplied but no array of control commands;
ENGINE_HAS_CTRL_FUNCTION returns TRUE,
all other commands fail.
if a ctrl() handler and array of control commands was supplied;
ENGINE_HAS_CTRL_FUNCTION returns TRUE,
all other commands proceed processing ...
If the ENGINE's array of control commands is empty then all other commands will
fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the identifier of the
first command supported by the ENGINE, ENGINE_GET_NEXT_CMD_TYPE takes the
identifier of a command supported by the ENGINE and returns the next command
identifier or fails if there are no more, ENGINE_CMD_FROM_NAME takes a string
name for a command and returns the corresponding identifier or fails if no
such command name exists, and the remaining commands take a command identifier
and return properties of the corresponding commands. All except
ENGINE_CTRL_GET_FLAGS return the string length of a command name or
description, or populate a supplied character buffer with a copy of the
command name or description. ENGINE_CTRL_GET_FLAGS returns a bitwise-OR'd mask
of the following possible values:
ENGINE_CMD_FLAG_NUMERIC
ENGINE_CMD_FLAG_STRING
ENGINE_CMD_FLAG_NO_INPUT
ENGINE_CMD_FLAG_INTERNAL
If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any other flags are purely
informational to the caller - this flag will prevent the command being usable
for any higher-level ENGINE functions such as
ENGINE_ctrl_cmd_string().
"INTERNAL" commands are not intended to be exposed to text-based
configuration by applications, administrations, users, etc. These can support
arbitrary operations via
ENGINE_ctrl(), including passing to and/or
from the control commands data of any arbitrary type. These commands are
supported in the discovery mechanisms simply to allow applications to
determine if an ENGINE supports certain specific commands it might want to use
(e.g. application "foo" might query various ENGINEs to see if they
implement "FOO_GET_VENDOR_LOGO_GIF" - and ENGINE could therefore
decide whether or not to support this "foo"-specific extension).
- OPENSSL_ENGINES
- The path to the engines directory. Ignored in set-user-ID
and set-group-ID programs.
ENGINE_get_first(),
ENGINE_get_last(),
ENGINE_get_next()
and
ENGINE_get_prev() return a valid
ENGINE structure or NULL if
an error occurred.
ENGINE_add() and
ENGINE_remove() return 1 on success or 0 on
error.
ENGINE_by_id() returns a valid
ENGINE structure or NULL if an
error occurred.
ENGINE_init() and
ENGINE_finish() return 1 on success or 0 on
error.
All
ENGINE_get_default_TYPE() functions,
ENGINE_get_cipher_engine() and
ENGINE_get_digest_engine() return
a valid
ENGINE structure on success or NULL if an error occurred.
All
ENGINE_set_default_TYPE() functions return 1 on success or 0 on
error.
ENGINE_set_default() returns 1 on success or 0 on error.
ENGINE_get_table_flags() returns an unsigned integer value representing
the global table flags which are used to control the registration behaviour of
ENGINE implementations.
All
ENGINE_register_TYPE() functions return 1 on success or 0 on error.
ENGINE_register_complete() and
ENGINE_register_all_complete()
always return 1.
ENGINE_ctrl() returns a positive value on success or others on error.
ENGINE_cmd_is_executable() returns 1 if
cmd is executable or 0
otherwise.
ENGINE_ctrl_cmd() and
ENGINE_ctrl_cmd_string() return 1 on success
or 0 on error.
ENGINE_new() returns a valid
ENGINE structure on success or NULL
if an error occurred.
ENGINE_free() always returns 1.
ENGINE_up_ref() returns 1 on success or 0 on error.
ENGINE_set_id() and
ENGINE_set_name() return 1 on success or 0 on
error.
All other
ENGINE_set_* functions return 1 on success or 0 on error.
ENGINE_get_id() and
ENGINE_get_name() return a string representing
the identifier and the name of the ENGINE
e respectively.
ENGINE_get_RSA(),
ENGINE_get_DSA(),
ENGINE_get_DH() and
ENGINE_get_RAND() return corresponding method structures for each
algorithms.
ENGINE_get_destroy_function(),
ENGINE_get_init_function(),
ENGINE_get_finish_function(),
ENGINE_get_ctrl_function(),
ENGINE_get_load_privkey_function(),
ENGINE_get_load_pubkey_function(),
ENGINE_get_ciphers() and
ENGINE_get_digests() return corresponding function pointers of the
callbacks.
ENGINE_get_cipher() returns a valid
EVP_CIPHER structure on
success or NULL if an error occurred.
ENGINE_get_digest() returns a valid
EVP_MD structure on success or
NULL if an error occurred.
ENGINE_get_flags() returns an integer representing the ENGINE flags which
are used to control various behaviours of an ENGINE.
ENGINE_get_cmd_defns() returns an
ENGINE_CMD_DEFN structure or
NULL if it's not set.
ENGINE_load_private_key() and
ENGINE_load_public_key() return a
valid
EVP_PKEY structure on success or NULL if an error occurred.
OPENSSL_init_crypto(3),
RSA_new_method(3),
DSA_new(3),
DH_new(3),
RAND_bytes(3),
config(5)
All of these functions were deprecated in OpenSSL 3.0.
ENGINE_cleanup() was deprecated in OpenSSL 1.1.0 by the automatic cleanup
done by
OPENSSL_cleanup() and should not be used.
Copyright 2002-2021 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>.