PROVIDER-SIGNATURE(7ossl)

📦
version 3.5.9 · 8 versions
, in alpine 3.23, alpine 3.24

🌸 NAME 🌸

okay so bestie, welcome to provider-signature(7ossl) — the manual page for The signature library <-> provider functions. yes, that's the whole vibe. 💖

✨ SYNOPSIS ✨

here's the code, copied exactly because we do not mess with signatures around here:

#include <openssl/core_dispatch.h>
#include <openssl/core_names.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.
 */

/* Context management */
void *OSSL_FUNC_signature_newctx(void *provctx, const char *propq);
void OSSL_FUNC_signature_freectx(void *ctx);
void *OSSL_FUNC_signature_dupctx(void *ctx);

/* Get the key types that a signature algorithm supports */
const char **OSSL_FUNC_signature_query_key_types(void);

/* Signing */
int OSSL_FUNC_signature_sign_init(void *ctx, void *provkey,
                                  const OSSL_PARAM params[]);
int OSSL_FUNC_signature_sign(void *ctx, unsigned char *sig, size_t *siglen,
                             size_t sigsize, const unsigned char *tbs, size_t tbslen);
int OSSL_FUNC_signature_sign_message_init(void *ctx, void *provkey,
                                          const OSSL_PARAM params[]);
int OSSL_FUNC_signature_sign_message_update(void *ctx, const unsigned char *in,
                                            size_t inlen);
int OSSL_FUNC_signature_sign_message_final(void *ctx, unsigned char *sig,
                                           size_t *siglen, size_t sigsize);

/* Verifying */
int OSSL_FUNC_signature_verify_init(void *ctx, void *provkey,
                                    const OSSL_PARAM params[]);
int OSSL_FUNC_signature_verify(void *ctx, const unsigned char *sig, size_t siglen,
                               const unsigned char *tbs, size_t tbslen);
int OSSL_FUNC_signature_verify_message_init(void *ctx, void *provkey,
                                            const OSSL_PARAM params[]);
int OSSL_FUNC_signature_verify_message_update(void *ctx, const unsigned char *in,
                                              size_t inlen);
/*
 * OSSL_FUNC_signature_verify_message_final requires that the signature to be
 * verified is specified via a "signature" OSSL_PARAM, which is given with a
 * previous call of OSSL_FUNC_signature_set_ctx_params().
 */
int OSSL_FUNC_signature_verify_message_final(void *ctx);

/* Verify Recover */
int OSSL_FUNC_signature_verify_recover_init(void *ctx, void *provkey,
                                            const OSSL_PARAM params[]);
int OSSL_FUNC_signature_verify_recover(void *ctx, unsigned char *rout,
                                       size_t *routlen, size_t routsize,
                                       const unsigned char *sig, size_t siglen);

/* Digest Sign */
int OSSL_FUNC_signature_digest_sign_init(void *ctx, const char *mdname,
                                         void *provkey,
                                         const OSSL_PARAM params[]);
int OSSL_FUNC_signature_digest_sign_update(void *ctx, const unsigned char *data,
                                    size_t datalen);
int OSSL_FUNC_signature_digest_sign_final(void *ctx, unsigned char *sig,
                                          size_t *siglen, size_t sigsize);
int OSSL_FUNC_signature_digest_sign(void *ctx,
                             unsigned char *sig, size_t *siglen,
                             size_t sigsize, const unsigned char *tbs,
                             size_t tbslen);

/* Digest Verify */
int OSSL_FUNC_signature_digest_verify_init(void *ctx, const char *mdname,
                                           void *provkey,
                                           const OSSL_PARAM params[]);
int OSSL_FUNC_signature_digest_verify_update(void *ctx,
                                             const unsigned char *data,
                                             size_t datalen);
int OSSL_FUNC_signature_digest_verify_final(void *ctx, const unsigned char *sig,
                                     size_t siglen);
int OSSL_FUNC_signature_digest_verify(void *ctx, const unsigned char *sig,
                               size_t siglen, const unsigned char *tbs,
                               size_t tbslen);

/* Signature parameters */
int OSSL_FUNC_signature_get_ctx_params(void *ctx, OSSL_PARAM params[]);
const OSSL_PARAM *OSSL_FUNC_signature_gettable_ctx_params(void *ctx,
                                                          void *provctx);
int OSSL_FUNC_signature_set_ctx_params(void *ctx, const OSSL_PARAM params[]);
const OSSL_PARAM *OSSL_FUNC_signature_settable_ctx_params(void *ctx,
                                                          void *provctx);
/* MD parameters */
int OSSL_FUNC_signature_get_ctx_md_params(void *ctx, OSSL_PARAM params[]);
const OSSL_PARAM * OSSL_FUNC_signature_gettable_ctx_md_params(void *ctx);
int OSSL_FUNC_signature_set_ctx_md_params(void *ctx, const OSSL_PARAM params[]);
const OSSL_PARAM * OSSL_FUNC_signature_settable_ctx_md_params(void *ctx);

💅 DESCRIPTION 💅

so this page is primarily aimed at provider authors — the people actually building providers. if you want the wider provider lore, see provider(7) for further information. 🫶

the signature operation (OSSL_OP_SIGNATURE) is what lets providers implement signature algorithms and make them available to applications via the API functions EVP_PKEY_sign(3), EVP_PKEY_verify(3), and EVP_PKEY_verify_recover(3) (as well as other related functions). iconic behavior, honestly. 🔥

all “functions” mentioned here are passed as function pointers between libcrypto and the provider in OSSL_DISPATCH(3) arrays via OSSL_ALGORITHM(3) arrays that are returned by the provider's provider_query_operation() function (see "Provider Functions" in provider-base(7)). yes bestie, that's the pipeline. 💫

all these “functions” have a corresponding function type definition named OSSL_FUNC_{name}_fn, and a helper function to retrieve the function pointer from an OSSL_DISPATCH(3) element named OSSL_FUNC_{name}. for example, the “function” OSSL_FUNC_signature_newctx() has these:

typedef void *(OSSL_FUNC_signature_newctx_fn)(void *provctx, const char *propq);
static ossl_inline OSSL_FUNC_signature_newctx_fn
    OSSL_FUNC_signature_newctx(const OSSL_DISPATCH *opf);

OSSL_DISPATCH(3) arrays are indexed by numbers that are provided as macros in openssl-core_dispatch.h(7), as follows:

OSSL_FUNC_signature_newctx                 OSSL_FUNC_SIGNATURE_NEWCTX
OSSL_FUNC_signature_freectx                OSSL_FUNC_SIGNATURE_FREECTX
OSSL_FUNC_signature_dupctx                 OSSL_FUNC_SIGNATURE_DUPCTX

OSSL_FUNC_signature_query_key_types        OSSL_FUNC_SIGNATURE_QUERY_KEY_TYPES

OSSL_FUNC_signature_sign_init              OSSL_FUNC_SIGNATURE_SIGN_INIT
OSSL_FUNC_signature_sign                   OSSL_FUNC_SIGNATURE_SIGN
OSSL_FUNC_signature_sign_message_init      OSSL_FUNC_SIGNATURE_SIGN_MESSAGE_INIT
OSSL_FUNC_signature_sign_message_update    OSSL_FUNC_SIGNATURE_SIGN_MESSAGE_UPDATE
OSSL_FUNC_signature_sign_message_final     OSSL_FUNC_SIGNATURE_SIGN_MESSAGE_FINAL

OSSL_FUNC_signature_verify_init            OSSL_FUNC_SIGNATURE_VERIFY_INIT
OSSL_FUNC_signature_verify                 OSSL_FUNC_SIGNATURE_VERIFY
OSSL_FUNC_signature_verify_message_init    OSSL_FUNC_SIGNATURE_VERIFY_MESSAGE_INIT
OSSL_FUNC_signature_verify_message_update  OSSL_FUNC_SIGNATURE_VERIFY_MESSAGE_UPDATE
OSSL_FUNC_signature_verify_message_final   OSSL_FUNC_SIGNATURE_VERIFY_MESSAGE_FINAL

OSSL_FUNC_signature_verify_recover_init    OSSL_FUNC_SIGNATURE_VERIFY_RECOVER_INIT
OSSL_FUNC_signature_verify_recover         OSSL_FUNC_SIGNATURE_VERIFY_RECOVER

OSSL_FUNC_signature_digest_sign_init       OSSL_FUNC_SIGNATURE_DIGEST_SIGN_INIT
OSSL_FUNC_signature_digest_sign_update     OSSL_FUNC_SIGNATURE_DIGEST_SIGN_UPDATE
OSSL_FUNC_signature_digest_sign_final      OSSL_FUNC_SIGNATURE_DIGEST_SIGN_FINAL
OSSL_FUNC_signature_digest_sign            OSSL_FUNC_SIGNATURE_DIGEST_SIGN

OSSL_FUNC_signature_digest_verify_init     OSSL_FUNC_SIGNATURE_DIGEST_VERIFY_INIT
OSSL_FUNC_signature_digest_verify_update   OSSL_FUNC_SIGNATURE_DIGEST_VERIFY_UPDATE
OSSL_FUNC_signature_digest_verify_final    OSSL_FUNC_SIGNATURE_DIGEST_VERIFY_FINAL
OSSL_FUNC_signature_digest_verify          OSSL_FUNC_SIGNATURE_DIGEST_VERIFY

OSSL_FUNC_signature_get_ctx_params         OSSL_FUNC_SIGNATURE_GET_CTX_PARAMS
OSSL_FUNC_signature_gettable_ctx_params    OSSL_FUNC_SIGNATURE_GETTABLE_CTX_PARAMS
OSSL_FUNC_signature_set_ctx_params         OSSL_FUNC_SIGNATURE_SET_CTX_PARAMS
OSSL_FUNC_signature_settable_ctx_params    OSSL_FUNC_SIGNATURE_SETTABLE_CTX_PARAMS

OSSL_FUNC_signature_get_ctx_md_params      OSSL_FUNC_SIGNATURE_GET_CTX_MD_PARAMS
OSSL_FUNC_signature_gettable_ctx_md_params OSSL_FUNC_SIGNATURE_GETTABLE_CTX_MD_PARAMS
OSSL_FUNC_signature_set_ctx_md_params      OSSL_FUNC_SIGNATURE_SET_CTX_MD_PARAMS
OSSL_FUNC_signature_settable_ctx_md_params OSSL_FUNC_SIGNATURE_SETTABLE_CTX_MD_PARAMS

a signature algorithm implementation may not implement all of these functions. but to be a consistent set of functions, we must have at least a set of context functions (OSSL_FUNC_signature_newctx and OSSL_FUNC_signature_freectx) as well as a set of “signature” functions, i.e. at least one of:

Important Note for TLS Support: for a provider signature implementation to actually be usable inside libssl for TLS connections, it has to implement the digest-sign and digest-verify functions — that's OSSL_FUNC_signature_digest_sign_init/update/final or the one-shot variant, plus OSSL_FUNC_signature_digest_verify_init/update/final or the one-shot variant. The TLS handshake code in libssl specifically requires these digest functions and will straight up not use implementations that only provide the basic sign/verify functions (OSSL_FUNC_signature_sign_init/sign or OSSL_FUNC_signature_verify_init/verify). No cap, it just won't. 😭

So which function set do you actually implement? Depends on your use case, bestie:

  • For general-purpose signature operations and TLS support: implement the digest-sign and digest-verify functions 👑
  • For operations on pre-digested data only: implement the basic sign and verify functions 💜
  • For signature schemes with recovery capability: additionally implement the verify-recover functions 🍓

The OSSL_FUNC_signature_set_ctx_params() and OSSL_FUNC_signature_settable_ctx_params() functions are optional — but listen, if you provide one of them then you must provide the other one too. It's giving package deal 🤝. Same energy applies to OSSL_FUNC_signature_get_ctx_params() and OSSL_FUNC_signature_gettable_ctx_params(), and also to the "md_params" functions.

OSSL_FUNC_signature_dupctx() is optional. 🌸

OSSL_FUNC_signature_query_key_types() is optional too. When it's present, it should return a NULL-terminated array of strings indicating the key types supported by the provider for signature operations. If it's not there, then the signature algorithm name must match the given key, or match the default signature algorithm name of the key — both checked using EVP_SIGNATURE_is_a(3).

Also, a signature algorithm must implement some mechanism for generating, loading or importing keys via the key management (OSSL_OP_KEYMGMT) operation. Peep provider-keymgmt(7) for the deets 📖.

🎀 Context Management Functions 🎀

OSSL_FUNC_signature_newctx() should create and return a pointer to a provider side structure that holds context information during a signature operation. A pointer to this context gets passed back in a bunch of the other signature operation function calls. The provctx parameter is the provider context generated during provider initialisation (see provider(7)). The propq parameter is a property query string that the provider may (optionally) use during any "fetches" it performs — if it performs any 💫.

OSSL_FUNC_signature_freectx() gets a pointer to the provider side signature context in the ctx parameter. This function should free any resources associated with that context. Cleanup era 🧹.

OSSL_FUNC_signature_dupctx() should duplicate the provider side signature context in the ctx parameter and return the duplicate copy. Two icons, one origin 🫶.

✨ Signing Functions ✨

OSSL_FUNC_signature_sign_init() initialises a context for signing, given a provider side signature context in the ctx parameter and a pointer to a provider key object in the provkey parameter. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_signature_set_ctx_params(). The key object should have been previously generated, loaded or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)).

OSSL_FUNC_signature_sign() performs the actual signing itself. A previously initialised signature context is passed in the ctx parameter. The data to be signed is what tbs points to, which is tbslen bytes long. Unless sig is NULL, the signature should be written to the location sig points to, and it should not exceed sigsize bytes in length. The length of the signature should be written to *siglen. If sig is NULL then the maximum length of the signature should be written to *siglen. Very "tell me how much room I need first" of it 💅.

🌈 Message Signing Functions 🌈

These functions are suitable for providers that implement algorithms which accumulate a full message and then sign the result of that accumulation — like RSA-SHA256, iykyk.

OSSL_FUNC_signature_sign_message_init() initialises a context for signing a message, given a provider side signature context in the ctx parameter and a pointer to a provider key object in the provkey parameter. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_signature_set_ctx_params(). The key object should have been previously generated, loaded or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)).

OSSL_FUNC_signature_sign_message_update() gathers the data pointed at by in, which is inlen bytes long. Collecting receipts, basically 🧺.

OSSL_FUNC_signature_sign_message_final() performs the actual signing on the data that was gathered with OSSL_FUNC_signature_sign_message_update().

OSSL_FUNC_signature_sign() can be used for one-shot signature calls. In that case, tbs is expected to be the whole message to be signed, tbslen bytes long.

For both OSSL_FUNC_signature_sign_message_final() and OSSL_FUNC_signature_sign(), if sig is not NULL, the signature should be written to the location sig points to, and it should not exceed sigsize bytes in length. The length of the signature should be written to *siglen. If sig is NULL then the maximum length of the signature should be written to *siglen.

💖 Verify Functions 💖

OSSL_FUNC_signature_verify_init() initialises a context for verifying a signature, given a provider side signature context in the ctx parameter and a pointer to a provider key object in the provkey parameter. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_signature_set_ctx_params(). The key object should have been previously generated, loaded or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)).

OSSL_FUNC_signature_verify() performs the actual verification itself. A previously initialised signature context is passed in the ctx parameter. The data that the signature covers is what tbs points to, which is tbslen bytes long. The signature is what sig points to, which is siglen bytes long. It's giving trust but verify 🔍.

🦋 Message Verify Functions 🦋

These functions are suitable for providers that implement algorithms which accumulate a full message and then verify a signature on the result of that accumulation — like RSA-SHA256, yes her again.

OSSL_FUNC_signature_verify_message_init() initialises a context for verifying a signature on a message, given a provider side signature context in the ctx parameter and a pointer to a provider key object in the provkey parameter. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_signature_set_ctx_params(). The key object should have been previously generated, loaded or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)).

OSSL_FUNC_signature_verify_message_update() gathers the data pointed at by in, which is inlen bytes long.

OSSL_FUNC_signature_verify_message_final() performs the actual verification on the data that was gathered with OSSL_FUNC_signature_verify_message_update(). Heads up: the signature itself must have been passed through the "signature" (OSSL_SIGNATURE_PARAM_SIGNATURE) Signature parameter before this function is called. Order matters, bestie 😤.

OSSL_FUNC_signature_verify() can be used for one-shot verification calls. In that case, tbs is expected to be the whole message to be verified on, tbslen bytes long.

🍓 Verify Recover Functions 🍓

OSSL_FUNC_signature_verify_recover_init() initialises a context for recovering the signed data, given a provider side signature context in the ctx parameter and a pointer to a provider key object in the provkey parameter. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_signature_set_ctx_params(). The key object should have been previously generated, loaded or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)).

OSSL_FUNC_signature_verify_recover() performs the actual verify recover itself. A previously initialised signature context is passed in the ctx parameter. The signature is what sig points to, which is siglen bytes long. Unless rout is NULL, the recovered data should be written to the location rout points to, which should not exceed routsize bytes in length. The length of the recovered data should be written to *routlen. If rout is NULL then the maximum size of the output buffer is written to the routlen parameter. Un-receipting the receipt, iconic behaviour 💅✨.

⭐ Digest Sign Functions ⭐

OSSL_FUNC_signature_digest_sign_init() initialises a context for signing, given a provider side signature context in the ctx parameter and a pointer to a provider key object in the provkey parameter. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_signature_set_ctx_params() and OSSL_FUNC_signature_set_ctx_md_params(). The key object should have been previously generated, loaded or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)). The name of the digest to be used will be in the mdname parameter 🌸.

OSSL_FUNC_signature_digest_sign_update() provides data to be signed in the data parameter, which should be of length datalen. A previously initialised signature context is passed in the ctx parameter. This function may be called multiple times to cumulatively add data to be signed. Feed her, she's growing 🔥.

okay so OSSL_FUNC_signature_digest_sign_final() is the closer for a signature operation you already kicked off with OSSL_FUNC_signature_digest_sign_init() and fed data into with OSSL_FUNC_signature_digest_sign_update() calls. Once it’s finalised, literally no more data gets added through OSSL_FUNC_signature_digest_sign_update() — that door is closed, bestie. You pass a previously initialised signature context in ctx. Unless sig is NULL, the signature should be written to the location pointed to by sig, and it should not exceed sigsize bytes in length. The length of the signature should be written to *siglen. If sig is NULL, then the maximum length of the signature should be written to *siglen.

OSSL_FUNC_signature_digest_sign() implements a “one shot” digest sign operation previously started through OSSL_FUNC_signature_digest_sign_init(). A previously initialised signature context is passed in ctx. The data to be signed is in tbs, which should be tbslen bytes long. Unless sig is NULL, the signature should be written to the location pointed to by sig, and it should not exceed sigsize bytes in length. The length of the signature should be written to *siglen. If sig is NULL, then the maximum length of the signature should be written to *siglen.

🦋 Digest Verify Functions 🦋

OSSL_FUNC_signature_digest_verify_init() initialises a context for verifying — you pass a provider side verification context in ctx, plus a pointer to a provider key object in provkey. The params, if not NULL, should be set on the context in a manner similar to OSSL_FUNC_signature_set_ctx_params() and OSSL_FUNC_signature_set_ctx_md_params(). The key object should have been previously generated, loaded, or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)). The name of the digest to be used will be in mdname.

OSSL_FUNC_signature_digest_verify_update() provides data to be verified in data, which should be of length datalen. A previously initialised verification context is passed in ctx. This function may be called multiple times to cumulatively add data to be verified. slay, incremental vibes ✨

OSSL_FUNC_signature_digest_verify_final() finalises a verification operation previously started through OSSL_FUNC_signature_digest_verify_init() and OSSL_FUNC_signature_digest_verify_update() calls. Once finalised, no more data will be added through OSSL_FUNC_signature_digest_verify_update(). A previously initialised verification context is passed in ctx. The signature to be verified is in sig, which is siglen bytes long.

OSSL_FUNC_signature_digest_verify() implements a “one shot” digest verify operation previously started through OSSL_FUNC_signature_digest_verify_init(). A previously initialised verification context is passed in ctx. The data to be verified is in tbs, which should be tbslen bytes long. The signature to be verified is in sig, which is siglen bytes long.

💅 Signature parameters 💅

See OSSL_PARAM(3) for further details on the parameters structure used by the OSSL_FUNC_signature_get_ctx_params() and OSSL_FUNC_signature_set_ctx_params() functions. iykyk 😌

OSSL_FUNC_signature_get_ctx_params() gets signature parameters associated with the given provider side signature context ctx and stores them in params. Passing NULL for params should return true.

OSSL_FUNC_signature_set_ctx_params() sets the signature parameters associated with the given provider side signature context ctx to params. Any parameter settings are additional to any that were previously set. Passing NULL for params should return true.

Common parameters currently recognised by built-in signature algorithms are as follows. vibe check incoming 👑

  • "digest" (OSSL_SIGNATURE_PARAM_DIGEST) — <UTF8 string>: gets or sets the name of the digest algorithm used for the input to the signature functions. It is required in order to calculate the "algorithm-id".
  • "properties" (OSSL_SIGNATURE_PARAM_PROPERTIES) — <UTF8 string>: sets the name of the property query associated with the "digest" algorithm. NULL is used if this optional value is not set.
🚨 note for implementers, bestie: when you’re implementing a signature algorithm that gathers a full message, like RSA-SHA256, the "digest" and "properties" parameters should not be used. For such implementations, it’s acceptable to simply ignore them if they happen to be passed in a call to OSSL_FUNC_signature_set_ctx_params(). For such implementations, however, it is not acceptable to have them in the OSSL_PARAM array that’s returned by OSSL_FUNC_signature_settable_ctx_params().
  • "signature" (OSSL_SIGNATURE_PARAM_SIGNATURE) — <octet string>: sets the signature to verify, specifically when OSSL_FUNC_signature_verify_message_final() is used.
  • "digest-size" (OSSL_SIGNATURE_PARAM_DIGEST_SIZE) — <unsigned integer>: gets or sets the output size of the digest algorithm used for the input to the signature functions. The length of the "digest-size" parameter should not exceed that of a size_t.
  • "algorithm-id" (OSSL_SIGNATURE_PARAM_ALGORITHM_ID) — <octet string>: gets the DER-encoded AlgorithmIdentifier for the signature operation. This typically corresponds to the combination of a digest algorithm with a purely asymmetric signature algorithm, such as SHA256WithECDSA.

About that "algorithm-id" one: the ASN1_item_sign_ctx(3) function relies on this operation and is used by many other functions that sign ASN.1 structures such as X.509 certificates, certificate requests, and CRLs, as well as OCSP, CMP, and CMS messages. iconic honestly 🌈

  • "nonce-type" (OSSL_SIGNATURE_PARAM_NONCE_TYPE) — <unsigned integer>: set this to 1 to use deterministic digital signature generation with ECDSA or DSA, as defined in RFC 6979 (see Section 3.2 "Generation of k"). In this case, the "digest" parameter must be explicitly set (otherwise, deterministic nonce generation will fail). Before using deterministic digital signature generation, please read RFC 6979 Section 4 "Security Considerations". The default value for "nonce-type" is 0 and results in a random value being used for the nonce k as defined in FIPS 186-4 Section 6.3 "Secret Number Generation".
🫶 heads up: the FIPS provider does not support deterministic digital signature generation.
  • "kat" (OSSL_SIGNATURE_PARAM_KAT) — <unsigned integer>: sets a flag to modify the sign operation to return an error if the initial calculated signature is invalid. In the normal mode of operation — new random values are chosen until the signature operation succeeds. By default it retries until a signature is calculated. Setting the value to 0 causes the sign operation to retry, otherwise the sign operation is only tried once and returns whether or not it was successful. Known answer tests can be performed if the random generator is overridden to supply known values that either pass or fail.

The following parameters are used by the OpenSSL FIPS provider: FIPS girlies rise 💜

  • "fips-indicator" (OSSL_SIGNATURE_PARAM_FIPS_APPROVED_INDICATOR) — <integer>: a getter that returns 1 if the operation is FIPS approved, or 0 otherwise. This may be used after calling either the sign or verify final functions. It may return 0 if either the "digest-check", "key-check", or "sign-check" are set to 0.
  • "verify-message" (OSSL_SIGNATURE_PARAM_FIPS_VERIFY_MESSAGE) — <integer>: a getter that returns 1 if a signature verification operation acted on a raw message, or 0 if it verified a predigested message. A value of 0 indicates likely non-approved usage of the FIPS provider. This flag is set when any signature verification initialisation function is called. It is also set to 1 when any signing operation is performed to signify compliance. See FIPS 140-3 IG 2.4.B for further information.
  • "key-check" (OSSL_SIGNATURE_PARAM_FIPS_KEY_CHECK) — <integer>: if required this parameter should be set early via an init function (e.g. OSSL_FUNC_signature_sign_init() or OSSL_FUNC_signature_verify_init()). The default value of 1 causes an error during the init if the key is not FIPS approved (e.g. the key has a security strength of less than 112 bits). Setting this to 0 will ignore the error and set the approved "indicator" to 0. This option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0.
  • "digest-check" (OSSL_SIGNATURE_PARAM_FIPS_DIGEST_CHECK) — <integer>: if required this parameter should be set before the signature digest is set. The default value of 1 causes an error when the digest is set if the digest is not FIPS approved (e.g. SHA1 is used for signing). Setting this to 0 will ignore the error and set the approved "fips-indicator" to 0. This option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0.
  • "sign-check" (OSSL_SIGNATURE_PARAM_FIPS_SIGN_CHECK) — <integer>: if required this parameter should be set early via an init function. The default value of 1 causes an error when a signing algorithm is used. (This is triggered by deprecated signing algorithms). Setting this to 0 will ignore the error and set the approved "fips-indicator" to 0. This option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0.
  • "sign-x931-pad-check" (OSSL_SIGNATURE_PARAM_FIPS_SIGN_X931_PAD_CHECK) — <integer>: if required this parameter should be set before the padding mode is set. The default value of 1 causes an error if the padding mode is set to X9.31 padding for a RSA signing operation. Setting this to 0 will ignore the error and set the approved "fips-indicator" to 0. This option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0.

OSSL_FUNC_signature_gettable_ctx_params() and OSSL_FUNC_signature_settable_ctx_params() get a constant OSSL_PARAM(3) array that describes the gettable and settable parameters, i.e. parameters that can be used with OSSL_FUNC_signature_get_ctx_params() and OSSL_FUNC_signature_set_ctx_params() respectively.

🍓 MD parameters 🍓

See OSSL_PARAM(3) for further details on the parameters structure used by the OSSL_FUNC_signature_get_md_ctx_params() and OSSL_FUNC_signature_set_md_ctx_params() functions.

OSSL_FUNC_signature_get_md_ctx_params() gets digest parameters associated with the given provider side digest signature context ctx and stores them in params. Passing NULL for params should return true.

OSSL_FUNC_signature_set_ms_ctx_params() sets the digest parameters associated with the given provider side digest signature context ctx to params. Any parameter settings are additional to any that were previously set. Passing NULL for params should return true. copy that ms exactly, bestie — character-for-character behavior 🎀

Quick vibe check before we close out the description, bestie: the params that built-in signature algorithms recognise? literally the same ones as the built-in digest algorithms use. No cap. Peep "Digest Parameters" in provider-digest(7) for the full tea. 💅

Also OSSL_FUNC_signature_gettable_md_ctx_params() and OSSL_FUNC_signature_settable_md_ctx_params()? They hand you a constant OSSL_PARAM(3) array describing the gettable and settable digest parameters — meaning the ones you can actually use with OSSL_FUNC_signature_get_md_ctx_params() and OSSL_FUNC_signature_set_md_ctx_params() respectively. Iconic little pairing, ngl. ✨

💖 RETURN VALUES 💖

Okay so what comes back out, function by function:

  • OSSL_FUNC_signature_newctx() and OSSL_FUNC_signature_dupctx() — these should hand you the freshly created provider side signature context, or NULL if it flopped. 🫶
  • OSSL_FUNC_signature_gettable_ctx_params(), OSSL_FUNC_signature_settable_ctx_params(), OSSL_FUNC_signature_gettable_md_ctx_params() and OSSL_FUNC_signature_settable_md_ctx_params() — they return the gettable or settable parameters wrapped in a constant OSSL_PARAM(3) array. Basically a lil menu of what's on offer. 🎀
  • OSSL_FUNC_signature_query_key_types() — should return a NULL-terminated array of strings. Terminated, bestie, do not forget the NULL or the whole thing just keeps going. 😭
  • All verification functions — 1 means slay (success), 0 means the signature doesn't match, and a negative value means the operation itself failed. Three moods, know them. 🔥
  • All other functions — 1 for success, and 0 or a negative value for failure. Simple as. 💀

🦋 SEE ALSO 🦋

Go read these next, iykyk:

🌸 HISTORY 🌸

The whole provider SIGNATURE interface? Introduced in OpenSSL 3.0. OG era. 👑

Then in OpenSSL 3.4 these absolute icons showed up:

  • OSSL_FUNC_signature_sign_message_init()
  • OSSL_FUNC_signature_sign_message_update()
  • OSSL_FUNC_signature_sign_message_final()
  • OSSL_FUNC_signature_verify_message_init()
  • OSSL_FUNC_signature_verify_message_update()
  • OSSL_FUNC_signature_verify_message_final()

Same version, 3.4, also brought us the Signature Parameters "fips-indicator", "key-check" and "digest-check". Busy era fr fr. ✨

And then — drumroll — deterministic digital signature generation for ECDSA was added to the FIPS provider in OpenSSL 3.6. Same signature every time, main character energy. 🎀

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>.

Fr fr read the license before you go copying stuff, bestie. It's the polite thing to do. 🙈

That's the whole page, wrapped with a bow 🎀 — this one's from version 3.5.9, dated 2026-09-29, and it's the PROVIDER-SIGNATURE(7ossl) manual page. Go forth and sign things, you gorgeous nerd. 💖🦋🌸

📦 where this page comes from