PROVIDER-SIGNATURE(7ossl)

📦
version 15.1 · 3 versions
, in freebsd 15.1

💅 NAME 💅

provider-signature — the signature library <-> provider functions, bestie. Yeah, this is OpenSSL, page PROVIDER-SIGNATURE(7ossl), and it's lowkey a whole thing. Sit down, grab a snack. 🍓

✨ SYNOPSIS ✨

Okay so first things first, the includes. Copied exactly, no cap:

#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.
 */

Real talk: none of these are actual functions, they're just displayed like this so you can see the function signatures for the stuff offered as function pointers in OSSL_DISPATCH arrays. Like, they're vibes of functions. Main character energy only. 👑

🫧 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);
Heads up bestie: OSSL_FUNC_signature_verify_message_final needs the signature you're verifying to be passed in through a "signature" OSSL_PARAM, and that param has to be given in an earlier call to OSSL_FUNC_signature_set_ctx_params(). Don't skip that step, it will not slay. 😭

🫧 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 🌸

Okay so this documentation is primarily aimed at provider authors — that's the whole audience, periodt. If you need more info on that whole world, go see provider(7). 🫶

The signature (OSSL_OP_SIGNATURE) operation is what lets providers implement signature algorithms and make them available to applications through the API functions EVP_PKEY_sign(3), EVP_PKEY_verify(3), and EVP_PKEY_verify_recover(3) (plus other related functions). Like, that's the pipeline. Iconic.

All the "functions" mentioned here? They get passed as function pointers between libcrypto and the provider inside OSSL_DISPATCH(3) arrays, which travel via OSSL_ALGORITHM(3) arrays that are returned by the provider's provider_query_operation() function (peep "Provider Functions" in provider-base(7)). It's giving relay race. 🏃‍♀️

🦋 The OSSL_FUNC_{name}_fn situation

Every single one of these "functions" has a matching function type definition named OSSL_FUNC_{name}_fn, plus a helper function that fetches the function pointer out of 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);

🦋 The dispatch index table

OSSL_DISPATCH(3) arrays are indexed by numbers that come from macros in openssl-core_dispatch.h(7), like this — literally the whole list, I'm not skipping a single one 🙈:

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

🧚 What you actually have to implement

A signature algorithm implementation is not required to implement all of these functions, okay? Nobody's forcing you. BUT — and this is the vibe check — to be a consistent set of functions you must have at least:

  • a set of context functions (OSSL_FUNC_signature_newctx and OSSL_FUNC_signature_freectx)

plus a set of "signature" functions, i.e. at least one of these bad boys:

🔥 Important Note for TLS Support: okay so if you want your provider signature implementation to be usable within libssl for TLS connections, it must 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 it 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). Like, it won't even look at them, no cap. 💀

So which function set should you implement? Honestly it 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 here's the catch: if one of them is provided then the other one must also be provided. Package deal, no exceptions. The same applies to the OSSL_FUNC_signature_get_ctx_params() and OSSL_FUNC_signature_gettable_ctx_params() functions, as well as the "md_params" functions. 🫶

The OSSL_FUNC_signature_dupctx() function is optional. It is not yet used by OpenSSL (so like, it's giving "reserved for future vibes").

The OSSL_FUNC_signature_query_key_types() function is optional too. When present, it should return a NULL-terminated array of strings indicating the key types supported by the provider for signature operations. Otherwise 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).

A signature algorithm must also implement some mechanism for generating, loading or importing keys via the key management (OSSL_OP_KEYMGMT) operation. See provider-keymgmt(7) for further details. ✨

💅 Context Management Functions

OSSL_FUNC_signature_newctx() should create and return a pointer to a provider side structure for holding context information during a signature operation. A pointer to this context will be passed back in a number of the other signature operation function calls. The parameter provctx is the provider context generated during provider initialisation (see provider(7)). The propq parameter is a property query string that may be (optionally) used by the provider during any "fetches" that it may perform (if it performs any).

OSSL_FUNC_signature_freectx() is passed 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.

✍️ 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 pointed to be the tbs parameter which is tbslen bytes long. Unless sig is NULL, the signature should be written to the location pointed to by the sig parameter 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. (Yes, that's how you ask "how much room do I need?" — iconic.)

📨 Message Signing Functions

These functions are suitable for providers that implement algorithms that accumulate a full message and sign the result of that accumulation, such as RSA-SHA256.

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.

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 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. 🌈

🔍 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 pointed to be the tbs parameter which is tbslen bytes long. The signature is pointed to by the sig parameter which is siglen bytes long.

🕵️ Message Verify Functions

These functions are suitable for providers that implement algorithms that accumulate a full message and verify a signature on the result of that accumulation, such as RSA-SHA256.

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(). The signature itself must have been passed through the "signature" (OSSL_SIGNATURE_PARAM_SIGNATURE) Signature parameter before this function is called. Like, don't forget that step, or it's not gonna work. 🙈

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 pointed to by the sig parameter which is siglen bytes long. Unless rout is NULL, the recovered data should be written to the location pointed to by the rout parameter 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.

🌸 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 it in chunks, bestie — it eats. 🍓)

OSSL_FUNC_signature_digest_sign_final() is the one that ties the bow on a signing op you already started with OSSL_FUNC_signature_digest_sign_init() and OSSL_FUNC_signature_digest_sign_update() calls. Once it's finalised, that's it — no more data gets added through OSSL_FUNC_signature_digest_sign_update(), the door is closed, periodt. You pass in a previously initialised signature context in the ctx parameter. Unless sig is NULL, the signature gets written to wherever sig points, and it must not exceed sigsize bytes in length (respect the budget bestie 💅). The length of the signature goes to *siglen. And if sig is NULL? Then the maximum length of the signature gets written to *siglen instead — a little "how much room do I need" preview, iconic.

OSSL_FUNC_signature_digest_sign() is the "one shot" digest sign operation — you started things off through OSSL_FUNC_signature_digest_sign_init(), and now you're doing it all in one go, no update loop needed ✨. A previously initialised signature context comes in via the ctx parameter. The data to be signed lives in tbs, which should be tbslen bytes long. Unless sig is NULL, the signature is written to wherever sig points and it should not exceed sigsize bytes in length, with the signature's length landing in *siglen. If sig is NULL, the maximum length of the signature gets written to *siglen. Same energy, different door 🫶.

🦋 Digest Verify Functions 🦋

OSSL_FUNC_signature_digest_verify_init() sets up a context for verifying — you hand it a provider side verification context in the ctx parameter, plus 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 OSSL_FUNC_signature_set_ctx_params() and OSSL_FUNC_signature_set_ctx_md_params(). That 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)), no cap. And the name of the digest you're gonna use? That lives in the mdname parameter.

OSSL_FUNC_signature_digest_verify_update() feeds in the data to be verified via the data parameter, which should be datalen bytes long. A previously initialised verification context comes in through ctx. You can call this function multiple times to cumulatively add data to be verified — stack it up, it's fine 💖.

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 gets added through OSSL_FUNC_signature_digest_verify_update() — done is done. A previously initialised verification context is passed in the ctx parameter. The signature to be verified is in sig, which is siglen bytes long. Go off, verify it 🔥.

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, and the signature to be verified is in sig, which is siglen bytes long. Short, sweet, verified 💅.

🌸 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 — it's the whole receipts situation.

  • 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 (yes, literally just that, it's a whole vibe check).
  • 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 — nothing gets wiped, bestie. Passing NULL for params should return true.

The common parameters currently recognised by built-in signature algorithms are as follows 👇

  • "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.
  • "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. 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. Like, it's everywhere, main character behaviour 👑.
  • "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 — 😭 do not skip this). 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 bestie 🚨: 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, and 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-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. It's the menu, basically 🎀.

🧚 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.
Ngl the second one is spelled set_ms_ctx_params up there, not set_md_ctx_params — that's literally what the page says, so type it exactly like that and don't come for me 🙈.

Okay so real talk: the parameters that built-in signature algorithms recognise are literally the exact same ones the built-in digest algorithms use. Same vibes, same list. Go peek at "Digest Parameters" in provider-digest(7) if you want the full rundown 💅

  • OSSL_FUNC_signature_gettable_md_ctx_params() and OSSL_FUNC_signature_settable_md_ctx_params() — these two hand you back a constant OSSL_PARAM(3) array describing the gettable and settable digest params. Translation: they tell you which parameters you're allowed to pass to OSSL_FUNC_signature_get_md_ctx_params() and OSSL_FUNC_signature_set_md_ctx_params() respectively 🎀

✨ RETURN VALUES ✨

Here's the tea on what each function should give back, bestie ☕

  • OSSL_FUNC_signature_newctx() and OSSL_FUNC_signature_dupctx() — should return 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() — return the gettable or settable parameters wrapped up in a constant OSSL_PARAM(3) array ✨
  • OSSL_FUNC_signature_query_key_types() — should return a NULL-terminated array of strings 🦋
  • All verification functions — return 1 for success, 0 for a non-matching signature, and a negative value if the operation itself failed. Three whole moods, periodt 💀
  • All other functions — return 1 for success and 0 or a negative value on failure 🌸

🌈 SEE ALSO 🌈

Like, go read these next, iykyk 👑

provider(7), "Provider Functions" in provider-base(7), OSSL_PARAM(3), OSSL_DISPATCH(3), OSSL_ALGORITHM(3), EVP_PKEY_sign(3), EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3), EVP_SIGNATURE_is_a(3), ASN1_item_sign_ctx(3)

🕰️ HISTORY 🕰️

A little lore drop for you 📖✨

  • The provider SIGNATURE interface was introduced in OpenSSL 3.0.
  • The 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() and OSSL_FUNC_signature_verify_message_final() functions were added in OpenSSL 3.4 👑
  • The Signature Parameters "fips-indicator", "key-check" and "digest-check" were added in OpenSSL 3.4.
  • Deterministic digital signature generation for ECDSA was added to the FIPS provider in OpenSSL 3.6 🔥

Copyright 2019-2025 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>.

And that's the whole page, bestie — you ate that 🫶 This one's from OpenSSL 3.5.6, dated 2026-04-07, and it's PROVIDER-SIGNATURE(7ossl) in case you need to cite it in the group chat 💖🎀

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