engine.pod

mediastreamer2是开源的网络传输媒体流的库

=pod

=head1 NAME

engine - ENGINE cryptographic module support

=head1 SYNOPSIS

 #include <openssl/engine.h>

 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_openssl(void);
 void ENGINE_load_dynamic(void);
 #ifndef OPENSSL_NO_STATIC_ENGINE
 void ENGINE_load_4758cca(void);
 void ENGINE_load_aep(void);
 void ENGINE_load_atalla(void);
 void ENGINE_load_chil(void);
 void ENGINE_load_cswift(void);
 void ENGINE_load_gmp(void);
 void ENGINE_load_nuron(void);
 void ENGINE_load_sureware(void);
 void ENGINE_load_ubsec(void);
 #endif
 void ENGINE_load_cryptodev(void);
 void ENGINE_load_builtin_engines(void);

 void ENGINE_cleanup(void);

 ENGINE *ENGINE_get_default_RSA(void);
 ENGINE *ENGINE_get_default_DSA(void);
 ENGINE *ENGINE_get_default_ECDH(void);
 ENGINE *ENGINE_get_default_ECDSA(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_ECDH(ENGINE *e);
 int ENGINE_set_default_ECDSA(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_ECDH(ENGINE *e);
 void ENGINE_unregister_ECDH(ENGINE *e);
 void ENGINE_register_all_ECDH(void);
 int ENGINE_register_ECDSA(ENGINE *e);
 void ENGINE_unregister_ECDSA(ENGINE *e);
 void ENGINE_register_all_ECDSA(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_STORE(ENGINE *e);
 void ENGINE_unregister_STORE(ENGINE *e);
 void ENGINE_register_all_STORE(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);

 int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg);
 void *ENGINE_get_ex_data(const ENGINE *e, int idx);

 int ENGINE_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func,
         CRYPTO_EX_dup *dup_func, CRYPTO_EX_free *free_func);

 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_ECDH(ENGINE *e, const ECDH_METHOD *dh_meth);
 int ENGINE_set_ECDSA(ENGINE *e, const ECDSA_METHOD *dh_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_STORE(ENGINE *e, const STORE_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 ECDH_METHOD *ENGINE_get_ECDH(const ENGINE *e);
 const ECDSA_METHOD *ENGINE_get_ECDSA(const ENGINE *e);
 const DH_METHOD *ENGINE_get_DH(const ENGINE *e);
 const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e);
 const STORE_METHOD *ENGINE_get_STORE(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);

 void ENGINE_add_conf_module(void);

=head1 DESCRIPTION

These functions create, manipulate, and use cryptographic modules in the
form of B<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 B<ENGINE>
implementation includes the following abstractions;

 RSA_METHOD - for providing alternative RSA implementations
 DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD,
       STORE_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

=head2 Reference counting and handles

Due to the modular nature of the ENGINE API, pointers to ENGINEs need to be
treated as handles - ie. 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) independantly.

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 B<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
initiliased 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
B<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 independantly. If you have a functional reference to an
ENGINE, you have a guarantee that the ENGINE has been initialised ready to
perform cryptographic operations and will remain uninitialised
until after you have released your reference.

I<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.

I<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 (eg. lack of
system drivers, no special hardware attached, etc), otherwise it will
return non-zero to indicate that the ENGINE is now operational and will
have allocated a new B<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, eg. 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.

=head2 Default implementations

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, (eg.
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