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=head1 NAME
- The basic OpenSSL library E<lt>-E<gt> provider functions
#include <openssl/core_dispatch.h>
* None of these are actual functions, but are displayed like this for
* the function signatures for functions that are offered as function
* pointers in OSSL_DISPATCH arrays.
/* Functions offered by libcrypto to the providers */
const OSSL_ITEM *core_gettable_params(const OSSL_CORE_HANDLE *handle);
int core_get_params(const OSSL_CORE_HANDLE *handle, OSSL_PARAM params[]);
typedef void (*OSSL_thread_stop_handler_fn)(void *arg);
int core_thread_start(const OSSL_CORE_HANDLE *handle,
OSSL_thread_stop_handler_fn handfn);
OPENSSL_CORE_CTX *core_get_libctx(const OSSL_CORE_HANDLE *handle);
void core_new_error(const OSSL_CORE_HANDLE *handle);
void core_set_error_debug(const OSSL_CORE_HANDLE *handle,
const char *file, int line, const char *func);
void core_vset_error(const OSSL_CORE_HANDLE *handle,
uint32_t reason, const char *fmt, va_list args);
* Some OpenSSL functionality is directly offered to providers via
* dispatch
void *CRYPTO_malloc(size_t num, const char *file, int line);
void *CRYPTO_zalloc(size_t num, const char *file, int line);
void *CRYPTO_memdup(const void *str, size_t siz,
const char *file, int line);
char *CRYPTO_strdup(const char *str, const char *file, int line);
char *CRYPTO_strndup(const char *str, size_t s,
const char *file, int line);
void CRYPTO_free(void *ptr, const char *file, int line);
void CRYPTO_clear_free(void *ptr, size_t num,
const char *file, int line);
void *CRYPTO_realloc(void *addr, size_t num,
const char *file, int line);
void *CRYPTO_clear_realloc(void *addr, size_t old_num, size_t num,
const char *file, int line);
void *CRYPTO_secure_malloc(size_t num, const char *file, int line);
void *CRYPTO_secure_zalloc(size_t num, const char *file, int line);
void CRYPTO_secure_free(void *ptr, const char *file, int line);
void CRYPTO_secure_clear_free(void *ptr, size_t num,
const char *file, int line);
int CRYPTO_secure_allocated(const void *ptr);
void OPENSSL_cleanse(void *ptr, size_t len);
OSSL_CORE_BIO *BIO_new_file(const char *filename, const char *mode);
OSSL_CORE_BIO *BIO_new_membuf(const void *buf, int len);
int BIO_read_ex(OSSL_CORE_BIO *bio, void *data, size_t data_len,
size_t *bytes_read);
int BIO_write_ex(OSSL_CORE_BIO *bio, const void *data, size_t data_len,
size_t *written);
int BIO_up_ref(OSSL_CORE_BIO *bio);
int BIO_free(OSSL_CORE_BIO *bio);
int BIO_vprintf(OSSL_CORE_BIO *bio, const char *format, va_list args);
int BIO_vsnprintf(char *buf, size_t n, const char *fmt, va_list args);
void self_test_cb(OPENSSL_CORE_CTX *ctx, OSSL_CALLBACK **cb, void **cbarg);
size_t get_entropy(const OSSL_CORE_HANDLE *handle,
unsigned char **pout, int entropy,
size_t min_len, size_t max_len);
void cleanup_entropy(const OSSL_CORE_HANDLE *handle,
unsigned char *buf, size_t len);
size_t get_nonce(const OSSL_CORE_HANDLE *handle,
unsigned char **pout, size_t min_len, size_t max_len,
const void *salt, size_t salt_len);
void cleanup_nonce(const OSSL_CORE_HANDLE *handle,
unsigned char *buf, size_t len);
/* Functions offered by the provider to libcrypto */
void provider_teardown(void *provctx);
const OSSL_ITEM *provider_gettable_params(void *provctx);
int provider_get_params(void *provctx, OSSL_PARAM params[]);
const OSSL_ALGORITHM *provider_query_operation(void *provctx,
int operation_id,
const int *no_store);
void provider_unquery_operation(void *provctx, int operation_id,
const OSSL_ALGORITHM *algs);
const OSSL_ITEM *provider_get_reason_strings(void *provctx);
int provider_get_capabilities(void *provctx, const char *capability,
OSSL_CALLBACK *cb, void *arg);
All "functions" mentioned here are passed as function pointers between
F<libcrypto> and the provider in B<OSSL_DISPATCH> arrays, in the call
of the provider initialization function. See L<provider(7)/Provider>
for a description of the initialization function.
All these "functions" have a corresponding function type definition
named B<OSSL_FUNC_{name}_fn>, and a helper function to retrieve the
function pointer from a B<OSSL_DISPATCH> element named
For example, the "function" core_gettable_params() has these:
typedef OSSL_PARAM *
(OSSL_FUNC_core_gettable_params_fn)(const OSSL_CORE_HANDLE *handle);
static ossl_inline OSSL_NAME_core_gettable_params_fn
OSSL_FUNC_core_gettable_params(const OSSL_DISPATCH *opf);
B<OSSL_DISPATCH> arrays are indexed by numbers that are provided as
macros in L<openssl-core_dispatch.h(7)>, as follows:
For I<in> (the B<OSSL_DISPATCH> array passed from F<libcrypto> to the
core_set_error_debug OSSL_FUNC_CORE_SET_ERROR_DEBUG
ossl_rand_get_entropy OSSL_FUNC_GET_ENTROPY
ossl_rand_cleanup_entropy OSSL_FUNC_CLEANUP_ENTROPY
ossl_rand_get_nonce OSSL_FUNC_GET_NONCE
ossl_rand_cleanup_nonce OSSL_FUNC_CLEANUP_NONCE
For I<*out> (the B<OSSL_DISPATCH> array passed from the provider to
provider_get_reason_strings OSSL_FUNC_PROVIDER_GET_REASON_STRINGS
=head2 Core functions
core_gettable_params() returns a constant array of descriptor
B<OSSL_PARAM>, for parameters that core_get_params() can handle.
core_get_params() retrieves parameters from the core for the given I<handle>.
See L</Core parameters> below for a description of currently known
The core_thread_start() function informs the core that the provider has started
an interest in the current thread. The core will inform the provider when the
thread eventually stops. It must be passed the I<handle> for this provider, as
well as a callback I<handfn> which will be called when the thread stops. The
callback will subsequently be called from the thread that is stopping and gets
passed the provider context as an argument. This may be useful to perform thread
specific clean up such as freeing thread local variables.
core_get_libctx() retrieves the library context in which the library
object for the current provider is stored, accessible through the I<handle>.
This may sometimes be useful if the provider wishes to store a
reference to its context in the same library context.
core_new_error(), core_set_error_debug() and core_set_error() are
building blocks for reporting an error back to the core, with
reference to the I<handle>.
=over 4
=item core_new_error()
allocates a new thread specific error record.
This corresponds to the OpenSSL function L<ERR_new(3)>.
=item core_set_error_debug()
sets debugging information in the current thread specific error
The debugging information includes the name of the file I<file>, the
line I<line> and the function name I<func> where the error occurred.
This corresponds to the OpenSSL function L<ERR_set_debug(3)>.
=item core_set_error()
sets the I<reason> for the error, along with any addition data.
The I<reason> is a number defined by the provider and used to index
the reason strings table that's returned by
The additional data is given as a format string I<fmt> and a set of
arguments I<args>, which are treated in the same manner as with
I<file> and I<line> may also be passed to indicate exactly where the
error occurred or was reported.
This corresponds to the OpenSSL function L<ERR_vset_error(3)>.
CRYPTO_malloc(), CRYPTO_zalloc(), CRYPTO_memdup(), CRYPTO_strdup(),
CRYPTO_strndup(), CRYPTO_free(), CRYPTO_clear_free(),
CRYPTO_realloc(), CRYPTO_clear_realloc(), CRYPTO_secure_malloc(),
CRYPTO_secure_zalloc(), CRYPTO_secure_free(),
CRYPTO_secure_clear_free(), CRYPTO_secure_allocated(),
BIO_new_file(), BIO_new_mem_buf(), BIO_read_ex(), BIO_up_ref(), BIO_free(),
BIO_vprintf(), OPENSSL_cleanse(), and OPENSSL_hexstr2buf()
correspond exactly to the public functions with the same name.
As a matter of fact, the pointers in the B<OSSL_DISPATCH> array are
direct pointers to those public functions. Note that the BIO functions take an
B<OSSL_CORE_BIO> type rather than the standard B<BIO> type. This is to ensure
that a provider does not mix BIOs from the core with BIOs used on the provider
side (the two are not compatible).
OSSL_SELF_TEST_set_callback() is used to set an optional callback that can be
passed into a provider. This may be ignored by a provider.
get_entropy() retrieves seeding material from the operating system.
The seeding material will have at least I<entropy> bytes of randomness and the
output will have at least I<min_len> and at most I<max_len> bytes.
The buffer address is stored in I<*pout> and the buffer length is
returned to the caller. On error, zero is returned.
cleanup_entropy() is used to clean up and free the buffer returned by
get_entropy(). The entropy pointer returned by get_entropy() is passed in
B<buf> and its length in B<len>.
get_nonce() retrieves a nonce using the passed I<salt> parameter
of length I<salt_len> and operating system specific information.
The I<salt> should contain uniquely identifying information and this is
included, in an unspecified manner, as part of the output.
The output is stored in a buffer which contrains at least I<min_len> and at
most I<max_len> bytes. The buffer address is stored in I<*pout> and the
buffer length returned to the caller. On error, zero is returned.
cleanup_nonce() is used to clean up and free the buffer returned by
get_nonce(). The nonce pointer returned by get_nonce() is passed in
B<buf> and its length in B<len>.
=head2 Provider functions
provider_teardown() is called when a provider is shut down and removed
from the core's provider store.
It must free the passed I<provctx>.
provider_gettable_params() should return a constant array of
descriptor B<OSSL_PARAM>, for parameters that provider_get_params()
can handle.
provider_get_params() should process the B<OSSL_PARAM> array
I<params>, setting the values of the parameters it understands.
provider_query_operation() should return a constant B<OSSL_ALGORITHM>
that corresponds to the given I<operation_id>.
It should indicate if the core may store a reference to this array by
setting I<*no_store> to 0 (core may store a reference) or 1 (core may
not store a reference).
provider_unquery_operation() informs the provider that the result of a
provider_query_operation() is no longer directly required and that the function
pointers have been copied. The I<operation_id> should match that passed to
provider_query_operation() and I<algs> should be its return value.
provider_get_reason_strings() should return a constant B<OSSL_ITEM>
array that provides reason strings for reason codes the provider may
use when reporting errors using core_put_error().
The provider_get_capabilities() function should call the callback I<cb> passing
it a set of B<OSSL_PARAM>s and the caller supplied argument I<arg>. The
B<OSSL_PARAM>s should provide details about the capability with the name given
in the I<capability> argument relevant for the provider context I<provctx>. If a
provider supports multiple capabilities with the given name then it may call the
callback multiple times (one for each capability). Capabilities can be useful for
describing the services that a provider can offer. For further details see the
L</CAPABILITIES> section below. It should return 1 on success or 0 on error.
The provider_self_test() function should perform known answer tests on a subset
of the algorithms that it uses, and may also verify the integrity of the
provider module. It should return 1 on success or 0 on error. It will return 1
if this function is not used.
None of these functions are mandatory, but a provider is fairly
useless without at least provider_query_operation(), and
provider_gettable_params() is fairly useless if not accompanied by
=head2 Provider parameters
provider_get_params() can return the following provider parameters to the core:
=over 4
=item "name" (B<OSSL_PROV_PARAM_NAME>) <UTF8 string ptr>
This points to a string that should give a unique name for the provider.
=item "version" (B<OSSL_PROV_PARAM_VERSION>) <UTF8 string ptr>
This points to a string that is a version number associated with this provider.
OpenSSL in-built providers use OPENSSL_VERSION_STR, but this may be different
for any third party provider. This string is for informational purposes only.
=item "buildinfo" (B<OSSL_PROV_PARAM_BUILDINFO>) <UTF8 string ptr>
This points to a string that is a build information associated with this provider.
OpenSSL in-built providers use OPENSSL_FULL_VERSION_STR, but this may be
different for any third party provider.
=item "status" (B<OSSL_PROV_PARAM_STATUS>) <unsigned integer>
This returns 0 if the provider has entered an error state, otherwise it returns
provider_gettable_params() should return the above parameters.
=head2 Core parameters
core_get_params() can retrieve the following core parameters for each provider:
=over 4
=item "openssl-version" (B<OSSL_PROV_PARAM_CORE_VERSION>) <UTF8 string ptr>
This points to the OpenSSL libraries' full version string, i.e. the string
expanded from the macro B<OPENSSL_VERSION_STR>.
=item "provider-name" (B<OSSL_PROV_PARAM_CORE_PROV_NAME>) <UTF8 string ptr>
This points to the OpenSSL libraries' idea of what the calling provider is named.
=item "module-filename" (B<OSSL_PROV_PARAM_CORE_MODULE_FILENAME>) <UTF8 string ptr>
This points to a string containing the full filename of the providers
module file.
Additionally, provider specific configuration parameters from the
config file are available, in dotted name form.
The dotted name form is a concatenation of section names and final
config command name separated by periods.
For example, let's say we have the following config example:
openssl_conf = openssl_init
providers = providers_sect
foo = foo_sect
activate = 1
data1 = 2
data2 = str
more = foo_more
data3 = foo,bar
The provider will have these additional parameters available:
=over 4
=item "activate"
pointing at the string "1"
=item "data1"
pointing at the string "2"
=item "data2"
pointing at the string "str"
=item "more.data3"
pointing at the string "foo,bar"
For more information on handling parameters, see L<OSSL_PARAM(3)> as
Capabilities describe some of the services that a provider can offer.
Applications can query the capabilities to discover those services.
=head3 "TLS-GROUP" Capability
The "TLS-GROUP" capability can be queried by libssl to discover the list of
TLS groups that a provider can support. Each group supported can be used for
I<key exchange> (KEX) or I<key encapsulation method> (KEM) during a TLS
TLS clients can advertise the list of TLS groups they support in the
supported_groups extension, and TLS servers can select a group from the offered
list that they also support. In this way a provider can add to the list of
groups that libssl already supports with additional ones.
Each TLS group that a provider supports should be described via the callback
passed in through the provider_get_capabilities function. Each group should have
the following details supplied (all are mandatory, except
=over 4
=item "tls-group-name" (B<OSSL_CAPABILITY_TLS_GROUP_NAME>) <UTF8 string>
The name of the group as given in the IANA TLS Supported Groups registry
=item "tls-group-name-internal" (B<OSSL_CAPABILITY_TLS_GROUP_NAME_INTERNAL>) <UTF8 string>
The name of the group as known by the provider. This could be the same as the
"tls-group-name", but does not have to be.
=item "tls-group-id" (B<OSSL_CAPABILITY_TLS_GROUP_ID>) <unsigned integer>
The TLS group id value as given in the IANA TLS Supported Groups registry.
=item "tls-group-alg" (B<OSSL_CAPABILITY_TLS_GROUP_ALG>) <UTF8 string>
The name of a Key Management algorithm that the provider offers and that should
be used with this group. Keys created should be able to support I<key exchange>
or I<key encapsulation method> (KEM), as implied by the optional
The algorithm must support key and parameter generation as well as the
key/parameter generation parameter, B<OSSL_PKEY_PARAM_GROUP_NAME>. The group
name given via "tls-group-name-internal" above will be passed via
B<OSSL_PKEY_PARAM_GROUP_NAME> when libssl wishes to generate keys/parameters.
=item "tls-group-sec-bits" (B<OSSL_CAPABILITY_TLS_GROUP_SECURITY_BITS>) <unsigned integer>
The number of bits of security offered by keys in this group. The number of bits
should be comparable with the ones given in table 2 and 3 of the NIST SP800-57
=item "tls-group-is-kem" (B<OSSL_CAPABILITY_TLS_GROUP_IS_KEM>) <unsigned integer>
Boolean flag to describe if the group should be used in I<key exchange> (KEX)
mode (0, default) or in I<key encapsulation method> (KEM) mode (1).
This parameter is optional: if not specified, KEX mode is assumed as the default
mode for the group.
In KEX mode, in a typical Diffie-Hellman fashion, both sides execute I<keygen>
then I<derive> against the peer public key. To operate in KEX mode, the group
implementation must support the provider functions as described in
In KEM mode, the client executes I<keygen> and sends its public key, the server
executes I<encapsulate> using the client's public key and sends back the
resulting I<ciphertext>, finally the client executes I<decapsulate> to retrieve
the same I<shared secret> generated by the server's I<encapsulate>. To operate
in KEM mode, the group implementation must support the provider functions as
described in L<provider-kem(7)>.
Both in KEX and KEM mode, the resulting I<shared secret> is then used according
to the protocol specification.
=item "tls-min-tls" (B<OSSL_CAPABILITY_TLS_GROUP_MIN_TLS>) <integer>
=item "tls-max-tls" (B<OSSL_CAPABILITY_TLS_GROUP_MAX_TLS>) <integer>
=item "tls-min-dtls" (B<OSSL_CAPABILITY_TLS_GROUP_MIN_DTLS>) <integer>
=item "tls-max-dtls" (B<OSSL_CAPABILITY_TLS_GROUP_MAX_DTLS>) <integer>
These parameters can be used to describe the minimum and maximum TLS and DTLS
versions supported by the group. The values equate to the on-the-wire encoding
of the various TLS versions. For example TLSv1.3 is 0x0304 (772 decimal), and
TLSv1.2 is 0x0303 (771 decimal). A 0 indicates that there is no defined minimum
or maximum. A -1 indicates that the group should not be used in that protocol.
This is an example of a simple provider made available as a
dynamically loadable module.
It implements the fictitious algorithm C<FOO> for the fictitious
operation C<BAR>.
#include <malloc.h>
#include <openssl/core.h>
#include <openssl/core_dispatch.h>
/* Errors used in this provider */
#define E_MALLOC 1
static const OSSL_ITEM reasons[] = {
{ E_MALLOC, "memory allocation failure" }.
{ 0, NULL } /* Termination */
* To ensure we get the function signature right, forward declare
* them using function types provided by openssl/core_dispatch.h
OSSL_FUNC_bar_newctx_fn foo_newctx;
OSSL_FUNC_bar_freectx_fn foo_freectx;
OSSL_FUNC_bar_init_fn foo_init;
OSSL_FUNC_bar_update_fn foo_update;
OSSL_FUNC_bar_final_fn foo_final;
OSSL_FUNC_provider_query_operation_fn p_query;
OSSL_FUNC_provider_get_reason_strings_fn p_reasons;
OSSL_FUNC_provider_teardown_fn p_teardown;
OSSL_provider_init_fn OSSL_provider_init;
OSSL_FUNC_core_put_error *c_put_error = NULL;
/* Provider context */
struct prov_ctx_st {
/* operation context for the algorithm FOO */
struct foo_ctx_st {
struct prov_ctx_st *provctx;
int b;
static void *foo_newctx(void *provctx)
struct foo_ctx_st *fooctx = malloc(sizeof(*fooctx));
if (fooctx != NULL)
fooctx->provctx = provctx;
c_put_error(provctx->handle, E_MALLOC, __FILE__, __LINE__);
return fooctx;
static void foo_freectx(void *fooctx)
static int foo_init(void *vfooctx)
struct foo_ctx_st *fooctx = vfooctx;
fooctx->b = 0x33;
static int foo_update(void *vfooctx, unsigned char *in, size_t inl)
struct foo_ctx_st *fooctx = vfooctx;
/* did you expect something serious? */
if (inl == 0)
return 1;
for (; inl-- > 0; in++)
*in ^= fooctx->b;
return 1;
static int foo_final(void *vfooctx)
struct foo_ctx_st *fooctx = vfooctx;
fooctx->b = 0x66;
static const OSSL_DISPATCH foo_fns[] = {
{ OSSL_FUNC_BAR_NEWCTX, (void (*)(void))foo_newctx },
{ OSSL_FUNC_BAR_FREECTX, (void (*)(void))foo_freectx },
{ OSSL_FUNC_BAR_INIT, (void (*)(void))foo_init },
{ OSSL_FUNC_BAR_UPDATE, (void (*)(void))foo_update },
{ OSSL_FUNC_BAR_FINAL, (void (*)(void))foo_final },
{ 0, NULL }
static const OSSL_ALGORITHM bars[] = {
{ "FOO", "provider=chumbawamba", foo_fns },
static const OSSL_ALGORITHM *p_query(void *provctx, int operation_id,
int *no_store)
switch (operation_id) {
return bars;
return NULL;
static const OSSL_ITEM *p_reasons(void *provctx)
return reasons;
static void p_teardown(void *provctx)
static const OSSL_DISPATCH prov_fns[] = {
{ OSSL_FUNC_PROVIDER_TEARDOWN, (void (*)(void))p_teardown },
{ OSSL_FUNC_PROVIDER_QUERY_OPERATION, (void (*)(void))p_query },
{ OSSL_FUNC_PROVIDER_GET_REASON_STRINGS, (void (*)(void))p_reasons },
{ 0, NULL }
int OSSL_provider_init(const OSSL_CORE_HANDLE *handle,
const OSSL_DISPATCH *in,
const OSSL_DISPATCH **out,
void **provctx)
struct prov_ctx_st *pctx = NULL;
for (; in->function_id != 0; in++)
switch (in->function_id) {
c_put_error = OSSL_FUNC_core_put_error(in);
*out = prov_fns;
if ((pctx = malloc(sizeof(*pctx))) == NULL) {
* ALEA IACTA EST, if the core retrieves the reason table
* regardless, that string will be displayed, otherwise not.
c_put_error(handle, E_MALLOC, __FILE__, __LINE__);
return 0;
pctx->handle = handle;
return 1;
This relies on a few things existing in F<openssl/core_dispatch.h>:
#define OSSL_OP_BAR 4711
typedef void *(OSSL_FUNC_bar_newctx_fn)(void *provctx);
static ossl_inline OSSL_FUNC_bar_newctx(const OSSL_DISPATCH *opf)
{ return (OSSL_FUNC_bar_newctx_fn *)opf->function; }
typedef void (OSSL_FUNC_bar_freectx_fn)(void *ctx);
static ossl_inline OSSL_FUNC_bar_newctx(const OSSL_DISPATCH *opf)
{ return (OSSL_FUNC_bar_freectx_fn *)opf->function; }
typedef void *(OSSL_FUNC_bar_init_fn)(void *ctx);
static ossl_inline OSSL_FUNC_bar_init(const OSSL_DISPATCH *opf)
{ return (OSSL_FUNC_bar_init_fn *)opf->function; }
typedef void *(OSSL_FUNC_bar_update_fn)(void *ctx,
unsigned char *in, size_t inl);
static ossl_inline OSSL_FUNC_bar_update(const OSSL_DISPATCH *opf)
{ return (OSSL_FUNC_bar_update_fn *)opf->function; }
typedef void *(OSSL_FUNC_bar_final_fn)(void *ctx);
static ossl_inline OSSL_FUNC_bar_final(const OSSL_DISPATCH *opf)
{ return (OSSL_FUNC_bar_final_fn *)opf->function; }
=head1 SEE ALSO
=head1 HISTORY
The concept of providers and everything surrounding them was
introduced in OpenSSL 3.0.
Copyright 2019-2021 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