PROVIDER-BASE(7ossl)

📦
version 15.1 · 3 versions
, in freebsd 15.1

🎀 PROVIDER-BASE 💅 (7ossl)

okay bestie, buckle up — this is provider-base(7ossl), the ✨literal✨ glue doc for the basic OpenSSL library <-> provider functions. it's the group chat rules between libcrypto and your provider, and honestly it's giving backstage-pass energy 🫶

✨ NAME ✨

provider-base — the basic OpenSSL library <-> provider functions 🔥

🌸 SYNOPSIS 🌸

no cap, just vibe with the code block:

#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,
                      void *arg);

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);

int core_obj_add_sigid(const OSSL_CORE_HANDLE *prov, const char  *sign_name,
                       const char *digest_name, const char *pkey_name);
int core_obj_create(const OSSL_CORE_HANDLE *handle, const char *oid,
                    const char *sn, const char *ln);

/*
 * 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_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);

unsigned char *OPENSSL_hexstr2buf(const char *str, long *buflen);

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 OSSL_SELF_TEST_set_callback(OSSL_LIB_CTX *libctx, 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);
size_t get_user_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);
void cleanup_user_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);
size_t get_user_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);
void cleanup_user_nonce(const OSSL_CORE_HANDLE *handle,
                        unsigned char *buf, size_t len);

/* Functions for querying the providers in the application library context */
int provider_register_child_cb(const OSSL_CORE_HANDLE *handle,
                    int (*create_cb)(const OSSL_CORE_HANDLE *provider,
                                     void *cbdata),
                    int (*remove_cb)(const OSSL_CORE_HANDLE *provider,
                                     void *cbdata),
                    int (*global_props_cb)(const char *props, void *cbdata),
                    void *cbdata);
void provider_deregister_child_cb(const OSSL_CORE_HANDLE *handle);
const char *provider_name(const OSSL_CORE_HANDLE *prov);
void *provider_get0_provider_ctx(const OSSL_CORE_HANDLE *prov);
const OSSL_DISPATCH *provider_get0_dispatch(const OSSL_CORE_HANDLE *prov);
int provider_up_ref(const OSSL_CORE_HANDLE *prov, int activate);
int provider_free(const OSSL_CORE_HANDLE *prov, int deactivate);

/* 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);
int provider_self_test(void *provctx);

🦋 DESCRIPTION 🦋

okay so here's the tea ☕ — every single "function" mentioned on this page isn't like, an actual callable C function you link against. they get passed around as function pointers between libcrypto and the provider, inside OSSL_DISPATCH(3) arrays, at the moment the provider initialization function gets called. if you wanna know what that init function actually is, go read "Provider" in provider(7) — it's got the whole description. these little guys are known as "upcalls" 💫

and every one of these "functions" has a matching function type definition named OSSL_FUNC_{name}_fn, plus a lil helper to go grab the function pointer out of an OSSL_DISPATCH(3) element, named OSSL_FUNC_{name}. so for example, the "function" core_gettable_params() has these besties:

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);

OSSL_DISPATCH(3) array entries each carry a function_id field that says which function it is, iykyk. those function_id numbers are handed to you as macros in openssl-core_dispatch.h(7), and here's the whole mapping, no skips 🫶

🎀 For in (the OSSL_DISPATCH(3) array passed from libcrypto to the provider):

  • core_gettable_params — OSSL_FUNC_CORE_GETTABLE_PARAMS
  • core_get_params — OSSL_FUNC_CORE_GET_PARAMS
  • core_thread_start — OSSL_FUNC_CORE_THREAD_START
  • core_get_libctx — OSSL_FUNC_CORE_GET_LIBCTX
  • core_new_error — OSSL_FUNC_CORE_NEW_ERROR
  • core_set_error_debug — OSSL_FUNC_CORE_SET_ERROR_DEBUG
  • core_vset_error — OSSL_FUNC_CORE_VSET_ERROR
  • core_set_error_mark — OSSL_FUNC_CORE_SET_ERROR_MARK
  • core_clear_last_error_mark — OSSL_FUNC_CORE_CLEAR_LAST_ERROR_MARK
  • core_pop_error_to_mark — OSSL_FUNC_CORE_POP_ERROR_TO_MARK
  • core_count_to_mark — OSSL_FUNC_CORE_COUNT_TO_MARK
  • core_obj_add_sigid — OSSL_FUNC_CORE_OBJ_ADD_SIGID
  • core_obj_create — OSSL_FUNC_CORE_OBJ_CREATE
  • CRYPTO_malloc — OSSL_FUNC_CRYPTO_MALLOC
  • CRYPTO_zalloc — OSSL_FUNC_CRYPTO_ZALLOC
  • CRYPTO_free — OSSL_FUNC_CRYPTO_FREE
  • CRYPTO_clear_free — OSSL_FUNC_CRYPTO_CLEAR_FREE
  • CRYPTO_realloc — OSSL_FUNC_CRYPTO_REALLOC
  • CRYPTO_clear_realloc — OSSL_FUNC_CRYPTO_CLEAR_REALLOC
  • CRYPTO_secure_malloc — OSSL_FUNC_CRYPTO_SECURE_MALLOC
  • CRYPTO_secure_zalloc — OSSL_FUNC_CRYPTO_SECURE_ZALLOC
  • CRYPTO_secure_free — OSSL_FUNC_CRYPTO_SECURE_FREE
  • CRYPTO_secure_clear_free — OSSL_FUNC_CRYPTO_SECURE_CLEAR_FREE
  • CRYPTO_secure_allocated — OSSL_FUNC_CRYPTO_SECURE_ALLOCATED
  • BIO_new_file — OSSL_FUNC_BIO_NEW_FILE
  • BIO_new_mem_buf — OSSL_FUNC_BIO_NEW_MEMBUF
  • BIO_read_ex — OSSL_FUNC_BIO_READ_EX
  • BIO_write_ex — OSSL_FUNC_BIO_WRITE_EX
  • BIO_up_ref — OSSL_FUNC_BIO_UP_REF
  • BIO_free — OSSL_FUNC_BIO_FREE
  • BIO_vprintf — OSSL_FUNC_BIO_VPRINTF
  • BIO_vsnprintf — OSSL_FUNC_BIO_VSNPRINTF
  • BIO_puts — OSSL_FUNC_BIO_PUTS
  • BIO_gets — OSSL_FUNC_BIO_GETS
  • BIO_ctrl — OSSL_FUNC_BIO_CTRL
  • OPENSSL_cleanse — OSSL_FUNC_OPENSSL_CLEANSE
  • OSSL_SELF_TEST_set_callback — OSSL_FUNC_SELF_TEST_CB
  • ossl_rand_get_entropy — OSSL_FUNC_GET_ENTROPY
  • ossl_rand_get_user_entropy — OSSL_FUNC_GET_USER_ENTROPY
  • ossl_rand_cleanup_entropy — OSSL_FUNC_CLEANUP_ENTROPY
  • ossl_rand_cleanup_user_entropy — OSSL_FUNC_CLEANUP_USER_ENTROPY
  • ossl_rand_get_nonce — OSSL_FUNC_GET_NONCE
  • ossl_rand_get_user_nonce — OSSL_FUNC_GET_USER_NONCE
  • ossl_rand_cleanup_nonce — OSSL_FUNC_CLEANUP_NONCE
  • ossl_rand_cleanup_user_nonce — OSSL_FUNC_CLEANUP_USER_NONCE
  • provider_register_child_cb — OSSL_FUNC_PROVIDER_REGISTER_CHILD_CB
  • provider_deregister_child_cb — OSSL_FUNC_PROVIDER_DEREGISTER_CHILD_CB
  • provider_name — OSSL_FUNC_PROVIDER_NAME
  • provider_get0_provider_ctx — OSSL_FUNC_PROVIDER_GET0_PROVIDER_CTX
  • provider_get0_dispatch — OSSL_FUNC_PROVIDER_GET0_DISPATCH
  • provider_up_ref — OSSL_FUNC_PROVIDER_UP_REF
  • provider_free — OSSL_FUNC_PROVIDER_FREE

💜 For *out (the OSSL_DISPATCH(3) array passed from the provider to libcrypto):

provider_teardown              OSSL_FUNC_PROVIDER_TEARDOWN
provider_gettable_params       OSSL_FUNC_PROVIDER_GETTABLE_PARAMS
provider_get_params            OSSL_FUNC_PROVIDER_GET_PARAMS
provider_query_operation       OSSL_FUNC_PROVIDER_QUERY_OPERATION
provider_unquery_operation     OSSL_FUNC_PROVIDER_UNQUERY_OPERATION
provider_get_reason_strings    OSSL_FUNC_PROVIDER_GET_REASON_STRINGS
provider_get_capabilities      OSSL_FUNC_PROVIDER_GET_CAPABILITIES
provider_self_test             OSSL_FUNC_PROVIDER_SELF_TEST

🫶 Core functions 🫶

Okay so core_gettable_params() hands you back a constant array of descriptor OSSL_PARAM(3), and it's literally just the list of params that core_get_params() knows how to deal with. That's it, that's the whole vibe.

core_get_params() is the one that actually fetches those parameters from the core for the handle you gave it. Wanna know what params exist? Scroll to "Core parameters" below, bestie, it's all there 👇

core_thread_start() is how you tell the core "hey, this provider is interested in the current thread". Then the core does the polite thing and lets you know when that thread eventually stops. You have to pass it the handle for this provider, plus a callback handfn that gets called when the thread stops. That callback gets called later (from the thread that's stopping, no less) and gets the provider context handed to it as an argument. Super useful if you need thread-specific cleanup, like freeing thread local variables. Lowkey iconic for tidying up 🧹

core_get_libctx() grabs you the core context where the library object for the current provider lives — you reach it through the handle. Important though: this one is useful only for built-in providers, like the default provider. Never cast this to OSSL_LIB_CTX in a provider that isn't built-in, because the OSSL_LIB_CTX of the library loading the provider might be a completely different structure than the OSSL_LIB_CTX of the library the provider is linked to. That's a whole mess you do not want 💀 Use OSSL_LIB_CTX_new_child(3) instead to get a proper library context that's linked to the application library context.

Fr fr, do not cast. That's not a vibe check you want to fail.

core_new_error(), core_set_error_debug() and core_vset_error() are the building blocks for reporting an error back to the core, all with reference to the handle. Let's break them down:

  • core_new_error() — allocates a new thread specific error record. This corresponds to the OpenSSL function ERR_new(3).
  • core_set_error_debug() — sets debugging information in the current thread specific error record. The debugging info includes the name of the file file, the line line and the function name func where the error occurred. This corresponds to the OpenSSL function ERR_set_debug(3).
  • core_vset_error() — sets the reason for the error, along with any addition data. The reason is a number defined by the provider, and it's used to index the reason strings table that's returned by provider_get_reason_strings(). The additional data comes as a format string fmt and a set of arguments args, which are treated the same manner as with BIO_vsnprintf(). You can also pass file and line to indicate exactly where the error occurred or was reported. This corresponds to the OpenSSL function ERR_vset_error(3).

Then there's the mark squad 🎀 — these all deal with marks on the error stack:

  • core_set_error_mark() — sets a mark on the current topmost error record, if there even is one. This corresponds to the OpenSSL function ERR_set_mark(3).
  • core_clear_last_error_mark() — removes the last mark added, if there is one. This corresponds to the OpenSSL function ERR_clear_last_mark(3).
  • core_pop_error_to_mark() — pops the top of the error stack until a mark is found. The mark then gets removed too. And if there's no mark at all? The whole stack is removed. Bye 👋 This corresponds to the OpenSSL function ERR_pop_to_mark(3).
  • core_count_to_mark() — returns the number of entries on the error stack above the most recently marked entry, not including that entry. If there's no mark in the error stack, then it just returns the number of entries in the error stack. This corresponds to the OpenSSL function ERR_count_to_mark(3).

core_obj_create() registers a brand new OID plus its associated short name sn and long name ln for the given handle. It's basically the OpenSSL function OBJ_create(3), except it returns 1 on success or 0 on failure. And here's the lil plot twist: it treats it as a success if the OID already exists — even if the short name sn or long name ln you passed as arguments differ from the ones already associated with that existing OID. In that case, though, the new names just don't get associated. No drama 🫶

core_obj_add_sigid() registers a new composite signature algorithm (sign_name) made up of an underlying signature algorithm (pkey_name) and a digest algorithm (digest_name) for the given handle. It assumes the OIDs for the composite signature algorithm — and for the underlying signature and digest algorithms too — are either already known to OpenSSL or have been registered via a call to core_obj_create(). This corresponds to the OpenSSL function OBJ_add_sigid(3), except the objects are identified by name rather than a numeric NID. Any name works for identifying the object — OID, short name or long name. And just like its sibling, it treats it as a success if the composite signature algorithm already exists, even if it was registered against a different underlying signature or digest algorithm. For digest_name, NULL or an empty string is permissible for signature algorithms that don't need a digest to operate correctly. Returns 1 on success or 0 on failure.

Okay, gather round, because this next bit is a big ol' list of things that correspond exactly to the public functions with the same name:

CRYPTO_malloc(), CRYPTO_zalloc(), 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_write_ex(), BIO_up_ref(), BIO_free(), BIO_vprintf(), BIO_vsnprintf(), BIO_gets(), BIO_puts(), BIO_ctrl(), OPENSSL_cleanse() and OPENSSL_hexstr2buf().

As a matter of fact, the pointers in the OSSL_DISPATCH(3) array are typically direct pointers to those public functions. Slay, no wrapper needed ✨

Careful though ⚠️ the BIO functions take an OSSL_CORE_BIO type rather than the standard BIO type. Why? To make sure a provider does not mix BIOs from the core with BIOs used on the provider side — the two are not compatible. Keep 'em separated, periodt.

OSSL_SELF_TEST_set_callback() is used to set an optional callback that can be passed into a provider. That said, a provider may just ignore it. Their loss 💅

get_entropy() retrieves seeding material from the operating system. The seeding material will have at least entropy bytes of randomness, and the output will have at least min_len and at most max_len bytes. The buffer address gets stored in *pout and the buffer length is returned to the caller. On error, zero is returned. 🙈

get_user_entropy() is literally the same as get_entropy() except it'll attempt to gather seed material via the seed source specified by a call to RAND_set_seed_source_type(3), or via "Random Configuration" in config(5). Cute.

cleanup_entropy() is the cleanup crew 🧹 — it cleans up and frees the buffer that get_entropy() returned. You pass the entropy pointer that get_entropy() gave you in buf, and its length in len.

cleanup_user_entropy() does the exact same thing but for the buffer returned by get_user_entropy(). Pass the nonce— sorry, the entropy pointer returned by get_user_entropy() in buf, and its length in len.

get_nonce() retrieves a nonce using the passed salt parameter of length salt_len plus operating system specific information. The salt should contain uniquely identifying information, and it gets included — in an unspecified manner — as part of the output. The output is stored in a buffer that contains at least min_len and at most max_len bytes. Buffer address goes in *pout, buffer length gets returned to the caller. On error, zero is returned. 🔥

get_user_nonce() is the same as get_nonce() except it'll attempt to gather seed material via the seed source specified by a call to RAND_set_seed_source_type(3), or via "Random Configuration" in config(5).

cleanup_nonce() cleans up and frees the buffer returned by get_nonce(). The nonce pointer that get_nonce() returned goes in buf, its length in len.

cleanup_user_nonce() cleans up and frees the buffer returned by get_user_nonce(). The nonce pointer returned by get_user_nonce() goes in buf, its length in len.

🌈 Child callbacks & friends 🌈

provider_register_child_cb() registers callbacks so you get informed about providers being loaded and unloaded in the application's library context. handle is this provider's handle, and cbdata is this provider's data — that's what gets passed back to the callbacks. Returns 1 on success or 0 otherwise.

⚠️ Deadlock warning, fr fr: these callbacks may be called while holding locks in libcrypto. So to avoid deadlocks, your callback implementation must not be long running and must not call other OpenSSL API functions or upcalls. Keep it short, keep it safe 💀
  • create_cb — a callback that gets called when a new provider is loaded into the application's library context. It's also called for any providers that are already loaded at the point that this callback is registered. The callback is passed the handle being used for the new provider being loaded, plus this provider's data in cbdata. It should return 1 on success or 0 on failure.
  • remove_cb — a callback that gets called when a new provider is unloaded from the application's library context. It's passed the handle being used for the provider being unloaded, plus this provider's data in cbdata. It should return 1 on success or 0 on failure.
  • global_props_cb — a callback that gets called when the global properties from the parent library context are changed. It should return 1 on success or 0 on failure.

provider_deregister_child_cb() unregisters callbacks that were previously registered via provider_register_child_cb(). And hey — if you did call provider_register_child_cb(), then you should call provider_deregister_child_cb() at or before the point that this provider's teardown function is called. Clean up after yourself, bestie 🎀

🦋 The rest of the provider-side helpers 🦋

  • provider_name() — returns a string giving the name of the provider identified by handle.
  • provider_get0_provider_ctx() — returns the provider context that's associated with the provider identified by prov.
  • provider_get0_dispatch() — gets the dispatch table that the provider identified by prov registered when it initialised.
  • provider_up_ref() — increments the reference count on the provider prov. If activate is nonzero then the provider is also loaded if it isn't already loaded. Returns 1 on success or 0 on failure.
  • provider_free() — decrements the reference count on the provider prov. If deactivate is nonzero then the provider is also unloaded if it is not already loaded. Returns 1 on success or 0 on failure.

Provider functions ✨

okay so these are the function pointers your provider hands over to the core — basically your provider's whole "here's how you talk to me" starter pack 💖

  • provider_teardown() — gets called when a provider is shut down and removed from the core's provider store. Its one job: free the passed provctx. that's it, that's the task 👑
  • provider_gettable_params() — should return a constant array of descriptor OSSL_PARAM(3), covering the parameters that provider_get_params() can handle.
  • provider_get_params() — should process the OSSL_PARAM(3) array params, setting the values of the parameters it understands.
  • provider_query_operation() — should return a constant OSSL_ALGORITHM(3) that corresponds to the given operation_id. It should also say whether the core is allowed to keep a reference to this array, by setting *no_store to 0 (core may store a reference) or 1 (core may not store a reference).
  • provider_unquery_operation() — this one 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 operation_id should match the one you passed to provider_query_operation(), and algs should be its return value 🫶
  • provider_get_reason_strings() — should return a constant OSSL_ITEM(3) array that provides reason strings for the reason codes the provider may use when reporting errors via core_put_error().
  • provider_get_capabilities() — this one should call the callback cb, passing it a set of OSSL_PARAM(3)s plus the caller-supplied argument arg. Those OSSL_PARAM(3)s should give details about the capability with the name given in the capability argument, relevant for the provider context provctx. If a provider supports multiple capabilities with the given name, it may call the callback multiple times (one for each capability). Capabilities are lowkey the vibe-check of what services a provider can offer. For further details see the "CAPABILITIES" section below. It should return 1 on success or 0 on error.
  • provider_self_test() — 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 ngl a provider is fairly useless without at least provider_query_operation(), and provider_gettable_params() is fairly useless if it's not accompanied by provider_get_params() 💀

Provider parameters 🎀

provider_get_params() can return the following provider parameters to the core:

  • "name" (OSSL_PROV_PARAM_NAME) <UTF8 ptr> — points to a string that should give a unique name for the provider.
  • "version" (OSSL_PROV_PARAM_VERSION) <UTF8 ptr> — 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. Heads up: this string is for informational purposes only.
  • "buildinfo" (OSSL_PROV_PARAM_BUILDINFO) <UTF8 ptr> — points to a string that is 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.
  • "status" (OSSL_PROV_PARAM_STATUS) <unsigned integer> — returns 0 if the provider has entered an error state, otherwise it returns 1.

provider_gettable_params() should return the above parameters.

Core parameters 🦋

core_get_params() can retrieve the following core parameters for each provider:

  • "openssl-version" (OSSL_PROV_PARAM_CORE_VERSION) <UTF8 string ptr> — points to the OpenSSL libraries' full version string, i.e. the string expanded from the macro OPENSSL_VERSION_STR.
  • "provider-name" (OSSL_PROV_PARAM_CORE_PROV_NAME) <UTF8 string ptr> — points to the OpenSSL libraries' idea of what the calling provider is named.
  • "module-filename" (OSSL_PROV_PARAM_CORE_MODULE_FILENAME) <UTF8 string ptr> — 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 the final config command name, separated by periods.

For example, let's say we have the following config example:

config_diagnostics = 1
openssl_conf = openssl_init

[openssl_init]
providers = providers_sect

[providers_sect]
foo = foo_sect

[foo_sect]
activate = 1
data1 = 2
data2 = str
more = foo_more

[foo_more]
data3 = foo,bar

The provider will have these additional parameters available:

  • "activate" — pointing at the string "1"
  • "data1" — pointing at the string "2"
  • "data2" — pointing at the string "str"
  • "more.data3" — pointing at the string "foo,bar"

For more information on handling parameters, see OSSL_PARAM(3) as OSSL_PARAM_int(3) 🫡

🌈 CAPABILITIES 🌈

Capabilities describe some of the services that a provider can offer. Applications can query the capabilities to discover those services ✨

The "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 key exchange (KEX) or key encapsulation method (KEM) during a TLS handshake. 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. no cap, that's genuinely iconic 👑

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 OSSL_CAPABILITY_TLS_GROUP_IS_KEM):

  • "tls-group-name" (OSSL_CAPABILITY_TLS_GROUP_NAME) <UTF8 string> — the name of the group as given in the IANA TLS Supported Groups registry: <https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-8>.
  • "tls-group-name-internal" (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 it does not have to be.
  • "tls-group-id" (OSSL_CAPABILITY_TLS_GROUP_ID) <unsigned integer> — the TLS group id value as given in the IANA TLS Supported Groups registry.

It is possible to register the same group id from within different providers. > Users should note that if no property query is specified, or more than one implementation matches the property query, then it is unspecified which implementation for a particular group id will be used. 😭

  • "tls-group-alg" (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 key exchange or key encapsulation method (KEM), as implied by the optional OSSL_CAPABILITY_TLS_GROUP_IS_KEM flag. The algorithm must support key and parameter generation, as well as the key/parameter generation parameter, OSSL_PKEY_PARAM_GROUP_NAME. The group name given via "tls-group-name-internal" above will be passed via OSSL_PKEY_PARAM_GROUP_NAME when libssl wishes to generate keys/parameters.
  • "tls-group-sec-bits" (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 document.
  • "tls-group-is-kem" (OSSL_CAPABILITY_TLS_GROUP_IS_KEM) <unsigned integer> — Boolean flag describing whether the group should be used in key exchange (KEX) mode (0, default) or in key encapsulation method (KEM) mode (1).

This parameter is optional: if it's 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 keygen then derive against the peer public key. To operate in KEX mode, the group implementation must support the provider functions as described in provider-keyexch(7).

In KEM mode, the client executes keygen and sends its public key, the server executes encapsulate using the client's public key and sends back the resulting ciphertext, and finally the client executes decapsulate to retrieve the same shared secret generated by the server's encapsulate. To operate in KEM mode, the group implementation must support the provider functions as described in provider-kem(7).

Both in KEX and KEM mode, the resulting shared secret is then used according to the protocol specification 🔥

  • "tls-min-tls" (OSSL_CAPABILITY_TLS_GROUP_MIN_TLS) <integer>, "tls-max-tls" (OSSL_CAPABILITY_TLS_GROUP_MAX_TLS) <integer>, "tls-min-dtls" (OSSL_CAPABILITY_TLS_GROUP_MIN_DTLS) <integer>, "tls-max-dtls" (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.

The "TLS-SIGALG" Capability ⭐

The "TLS-SIGALG" capability can be queried by libssl to discover the list of TLS signature algorithms that a provider can support. Each signature supported can be used for client- or server-authentication in addition to the built-in signature algorithms. TLS1.3 clients can advertise the list of TLS signature algorithms they support in the signature_algorithms extension, and TLS servers can select an algorithm from the offered list that they also support. In this way a provider can add to the list of signature algorithms that libssl already supports with additional ones 🙌

Each TLS signature algorithm that a provider supports should be described via the callback passed in through the provider_get_capabilities function. Each algorithm can have the following details supplied:

  • "iana-name" (OSSL_CAPABILITY_TLS_SIGALG_IANA_NAME) <UTF8 string> — the name of the signature algorithm as given in the IANA TLS Signature Scheme registry as "Description": <https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-signaturescheme>. This value must be supplied.
  • "iana-code-point" (OSSL_CAPABILITY_TLS_SIGALG_CODE_POINT) <unsigned integer> — the TLS algorithm ID value as given in the IANA TLS SignatureScheme registry. This value must be supplied.

Real talk, bestie: it’s totally possible to register the same code point from within different providers. But the vibe check is this: if no property query is specified, or more than one implementation matches the property query, then it is unspecified which implementation for a particular code point will be used. 💅

  • "sigalg-name" (OSSL_CAPABILITY_TLS_SIGALG_NAME) <UTF8 string> — the name for the full (possibly composite hash-and-signature) signature algorithm. The provider may, but is not obligated to, provide a signature implementation with this name; if it doesn’t, this is assumed to be a composite of a pure signature algorithm and a hash algorithm, which must be given with the parameters "sig-name" and "hash-name". This value must be supplied. 👑
  • "sigalg-oid" (OSSL_CAPABILITY_TLS_SIGALG_OID) <UTF8 string> — the OID of the "sigalg-name" algorithm in canonical numeric text form. If this parameter is given, OBJ_create() will be used to create an OBJ and a NID for this OID, using the "sigalg-name" parameter for its (short) name. Otherwise, it’s assumed to already exist in the object database, possibly done by the provider with the core_obj_create() upcall. This value is optional. ✨
  • "sig-name" (OSSL_CAPABILITY_TLS_SIGALG_SIG_NAME) <UTF8 string> — the name of the pure signature algorithm that is part of a composite "sigalg-name". If "sigalg-name" is implemented by the provider, this parameter is redundant and must not be given. This value is optional. 🎀
  • "sig-oid" (OSSL_CAPABILITY_TLS_SIGALG_SIG_OID) <UTF8 string> — the OID of the "sig-name" algorithm in canonical numeric text form. If this parameter is given, OBJ_create() will be used to create an OBJ and a NID for this OID, using the "sig-name" parameter for its (short) name. Otherwise, it is assumed to already exist in the object database. This can be done by the provider using the core_obj_create() upcall. This value is optional. 🦋
  • "hash-name" (OSSL_CAPABILITY_TLS_SIGALG_HASH_NAME) <UTF8 string> — the name of the hash algorithm that is part of a composite "sigalg-name". If "sigalg-name" is implemented by the provider, this parameter is redundant and must not be given. This value is optional. 🌸
  • "hash-oid" (OSSL_CAPABILITY_TLS_SIGALG_HASH_OID) <UTF8 string> — the OID of the "hash-name" algorithm in canonical numeric text form. If this parameter is given, OBJ_create() will be used to create an OBJ and a NID for this OID, using the "hash-name" parameter for its (short) name. Otherwise, it’s assumed to already exist in the object database, possibly done by the provider with the core_obj_create() upcall. This value is optional. 💅
  • "key-type" (OSSL_CAPABILITY_TLS_SIGALG_KEYTYPE) <UTF8 string> — the key type of the public key of applicable certificates. If this parameter isn’t present, it’s assumed to be the same as "sig-name" if that’s present, otherwise "sigalg-name". This value is optional. 🫶
  • "key-type-oid" (OSSL_CAPABILITY_TLS_SIGALG_KEYTYPE_OID) <UTF8 string> — the OID of the "key-type" in canonical numeric text form. If this parameter is given, OBJ_create() will be used to create an OBJ and a NID for this OID, using the "key-type" parameter for its (short) name. Otherwise, it’s assumed to already exist in the object database, possibly done by the provider with the core_obj_create() upcall. This value is optional. 😭
  • "sec-bits" (OSSL_CAPABILITY_TLS_SIGALG_SECURITY_BITS) <unsigned integer> — the number of bits of security offered by keys of this algorithm. The number of bits should be comparable with the ones given in table 2 and 3 of the NIST SP800-57 document. This number is used to determine the security strength of the algorithm if no digest algorithm has been registered that otherwise defines the security strength. If the signature algorithm implements its own digest internally, this value needs to be set to properly reflect the overall security strength. This value must be supplied. 🔥

These parameters can be used to describe the minimum and maximum TLS and DTLS versions supported by the signature algorithm. 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 in either the min or max field indicates that the signature algorithm should not be used in that protocol. Presently, provider signature algorithms are used only with TLS 1.3, if that’s enclosed in the specified range. 👑

  • "tls-min-tls" (OSSL_CAPABILITY_TLS_SIGALG_MIN_TLS) <integer> — minimum TLS version, same protocol-range tea as above. 🌈
  • "tls-max-tls" (OSSL_CAPABILITY_TLS_SIGALG_MAX_TLS) <integer> — maximum TLS version, same protocol-range tea as above. ⭐
  • "tls-min-dtls" (OSSL_CAPABILITY_TLS_SIGALG_MIN_DTLS) <integer> — minimum DTLS version, same protocol-range tea as above. 🧚
  • "tls-max-dtls" (OSSL_CAPABILITY_TLS_SIGALG_MAX_DTLS) <integer> — maximum DTLS version, same protocol-range tea as above. 💜

📝 NOTES

Tiny but important tea: the core_obj_create() and core_obj_add_sigid() functions were not thread safe in OpenSSL 3.0. 💀

🧪 EXAMPLES

This is an example of a simple provider made available as a dynamically loadable module. It implements the fictitious algorithm "FOO" for the fictitious operation "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" }.
            OSSL_DISPATCH_END
        };

        /*
         * 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 {
            OSSL_CORE_HANDLE *handle;
        }

        /* 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;
            else
                c_put_error(provctx->handle, E_MALLOC, __FILE__, __LINE__);
            return fooctx;
        }

        static void foo_freectx(void *fooctx)
        {
            free(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 },
            OSSL_DISPATCH_END
        };

        static const OSSL_ALGORITHM bars[] = {
            { "FOO", "provider=chumbawamba", foo_fns },
            { NULL, NULL, NULL }
        };

        static const OSSL_ALGORITHM *p_query(void *provctx, int operation_id,
                                             int *no_store)
        {
            switch (operation_id) {
            case OSSL_OP_BAR:
                return bars;
            }
            return NULL;
        }

        static const OSSL_ITEM *p_reasons(void *provctx)
        {
            return reasons;
        }

        static void p_teardown(void *provctx)
        {
            free(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 },
            OSSL_DISPATCH_END
        };

        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) {
                case OSSL_FUNC_CORE_PUT_ERROR:
                    c_put_error = OSSL_FUNC_core_put_error(in);
                    break;
                }

            *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 openssl/core_dispatch.h: 🌸

        #define OSSL_OP_BAR            4711

        #define OSSL_FUNC_BAR_NEWCTX      1
        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; }

        #define OSSL_FUNC_BAR_FREECTX     2
        typedef void (OSSL_FUNC_bar_freectx_fn)(void *ctx);
        static ossl_inline OSSL_FUNC_bar_freectx(const OSSL_DISPATCH *opf)
        { return (OSSL_FUNC_bar_freectx_fn *)opf->function; }

        #define OSSL_FUNC_BAR_INIT        3
        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; }

        #define OSSL_FUNC_BAR_UPDATE      4
        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; }

        #define OSSL_FUNC_BAR_FINAL       5
        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; }

👀 SEE ALSO

✨ HISTORY ✨

okay so story time bestie 📖 the whole concept of providers — and literally everything surrounding them — was introduced in OpenSSL 3.0. like, that's when the glow-up happened ✨ before that it was a whole different era, iykyk.

then later, the definitions for OSSL_CAPABILITY_TLS_SIGALG_MIN_DTLS and OSSL_CAPABILITY_TLS_SIGALG_MAX_DTLS got added in OpenSSL 3.5. so if you were wondering when those two iconic little constants showed up — that's the answer 💅

Copyright 2019-2026 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.

like fr fr read the license before you do stuff, bestie 🫶 it's right there.

and that's a wrap on PROVIDER-BASE(7ossl)! 🎀 this edition is from 3.5.6, dated 2026-04-07 — go forth and provider, queen 👑💜

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