PROVIDER-SIGNATURE(7SSL)

📦
version 4.0.3 · 13 versions
, in ubuntu stonking

✨ provider-signature(7SSL) ✨

okay bestie, gather round — this is provider-signature(7SSL), aka The signature library <-> provider functions. it's the page that tells you how the signature side of OpenSSL talks to providers. it's a chonky one so we're doing this in parts, stay with me 💖

🌸 SYNOPSIS 🌸

#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 real talk: this page is for the provider authors, the ones writing the guts. if you want the bigger picture, go peek at provider(7) — this page is like the directors' commentary, not the movie. 🎬

The signature operation — that's OSSL_OP_SIGNATURE — is the thing that lets providers cook up signature algorithms and serve them to apps through the real API besties: EVP_PKEY_sign(3), EVP_PKEY_verify(3), and EVP_PKEY_verify_recover(3) (plus all their little friend functions, they travel in packs 😌).

Every single "function" down here isn't a function function — it's a function pointer that gets passed between libcrypto and the provider inside OSSL_DISPATCH(3) arrays, which themselves live in OSSL_ALGORITHM(3) arrays handed back by the provider's provider_query_operation() function (check the "Provider Functions" section in provider-base(7) for that whole situation).

Now — because nothing here is a real function, each one has a matching function type definition called OSSL_FUNC_{name}_fn, AND a lil helper that goes and yoinks the function pointer out of an OSSL_DISPATCH(3) element, called OSSL_FUNC_{name}. take OSSL_FUNC_signature_newctx(), icon behavior incoming:

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 OSSL_DISPATCH(3) arrays get indexed by numbers, and those numbers are provided as macros over in openssl-core_dispatch.h(7). it's giving lookup table, and it goes like this:

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
heads up bestie: a signature algorithm implementation does not have to implement all of these. like, no pressure. ✋

But — and this is the vibe check — to be a consistent set of functions, you must have at least the context crew (OSSL_FUNC_signature_newctx and OSSL_FUNC_signature_freectx) plus a set of "signature" functions, meaning at least one of the following:

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

The choice of which function set to implement depends on your use case:

  • 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 if one of them is provided then the other one must also be provided. Same energy for the OSSL_FUNC_signature_get_ctx_params() and OSSL_FUNC_signature_gettable_ctx_params() functions, and for the "md_params" functions too.

The OSSL_FUNC_signature_dupctx() function is optional. ✨

The OSSL_FUNC_signature_query_key_types() function is optional. When it's 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 of those 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 provctx parameter 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. Clean up after yourself bestie.

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 by 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. 💅

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 — RSA-SHA256 is the blueprint bestie.

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 by 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 which accumulate a full message and verify a signature on the result of that accumulation — like RSA-SHA256, you guessed it 💅

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. Don't skip that step, fr fr.

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 rout, 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. 💖

OSSL_FUNC_signature_digest_sign_final() is the ✨grand finale✨ of a signature operation that you already started with OSSL_FUNC_signature_digest_sign_init() and kept feeding with OSSL_FUNC_signature_digest_sign_update() calls. Once you've finalised, that's it bestie — no more data is going in through OSSL_FUNC_signature_digest_sign_update(). You hand in a previously initialised signature context via the ctx parameter. If sig is not NULL, the signature gets written to the location sig points at, and it better not go over sigsize bytes. The length of the signature goes into *siglen. And if sig is NULL? Then the maximum possible length of the signature gets written to *siglen instead. 🎀

OSSL_FUNC_signature_digest_sign() is the "one shot" digest sign operation — and yes it still needs a OSSL_FUNC_signature_digest_sign_init() first, it's not that one-shot. Previously initialised signature context goes in ctx. The data you're signing lives in tbs, and it should be tbslen bytes long. Unless sig is NULL, the signature is written to wherever sig points and mustn't exceed sigsize bytes. Length of the signature goes to *siglen. And if sig is NULL, the maximum length of the signature gets written to *siglen. Same rules, different vibe check. 💅

🌸 Digest Verify Functions 🌸

OSSL_FUNC_signature_digest_verify_init() sets up a context for verifying — you pass a provider side verification context in ctx and 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(). 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) for the receipts. The name of the digest you're using goes in the mdname parameter. 🦋

OSSL_FUNC_signature_digest_verify_update() hands over data to be verified in the data parameter, which should be datalen long. A previously initialised verification context comes in via ctx. And she can be called multiple times, each call cumulatively adding more data to verify. Stack it up, bestie. 💖

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(). A previously initialised verification context goes in ctx. The signature to be verified is in sig, which is siglen bytes long. 🎀

OSSL_FUNC_signature_digest_verify() implements the "one shot" digest verify operation previously started through OSSL_FUNC_signature_digest_verify_init(). A previously initialised verification context goes 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. Boom, done, no extra steps. ✨

👑 Signature parameters 👑

Peep 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.

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 — nothing gets wiped. Passing NULL for params should return true.

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. She's kind of a big deal. 💅

  • "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" — fr fr, go read it. 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".

The FIPS provider does not support deterministic digital signature generation for DSA.

The FIPS provider supports deterministic digital signature generation for ECDSA.

  • "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.
Heads up 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(). But — and this part matters — for such implementations it is not acceptable to have them in the OSSL_PARAM array that's returned by OSSL_FUNC_signature_settable_ctx_params(). Do not do it. Periodt. 🙈

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()is the one that sets the digest parameters tied to your provider-side digest signature context *ctx* to *params*. And listen — every param you set is **additional** to whatever was already set before. It's giving ✨accumulation✨, not replacement. PassNULL` for params and it should return true. That's the whole vibe.

The parameters that built-in signature algorithms currently recognise are literally the same ones the built-in digest algorithms use — no cap, same list. Go read "Digest Parameters" over in provider-digest(7) for the full tea. 🫖

Then OSSL_FUNC_signature_gettable_md_ctx_params() and OSSL_FUNC_signature_settable_md_ctx_params() hand you a constant OSSL_PARAM(3) array describing the gettable and settable digest parameters respectively — like, the parameters you're allowed to use with OSSL_FUNC_signature_get_md_ctx_params() and OSSL_FUNC_signature_set_md_ctx_params(). Getters gonna get, setters gonna set 💅

💖 RETURN VALUES 💖

OSSL_FUNC_signature_newctx() and OSSL_FUNC_signature_dupctx() should return the brand-new provider-side signature context, or NULL if it all went wrong. 😭 That's the failure signal, remember it.

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 those gettable or settable parameters in a constant OSSL_PARAM(3) array. Constant. As in, don't you dare think about mutating it.

OSSL_FUNC_signature_query_key_types() should return a NULL-terminated array of strings. The NULL terminator is the little "and that's the end bestie" bookend, don't forget it.

Now the verification girlies have their own rulebook:

  • All verification functions should return 1 for success 🔥, 0 for a non-matching signature, and a negative value for operation failure.
  • All other functions should return 1 for success and 0 or a negative value for failure.

So 1 = ate, 0 = nope (or just failure for the non-verification ones), negative = something genuinely broke. 📉

🌈 SEE ALSO 🌈

Go read these next, bestie, they're all connected:

⭐ HISTORY ⭐

Okay so storytime 📖 The provider SIGNATURE interface made its debut in OpenSSL 3.0. Main character arrival, honestly.

Then 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() all got added in OpenSSL 3.4. Six glow-ups at once, we love to see it. ✨

The Signature Parameters "fips-indicator", "key-check" and "digest-check" also landed in OpenSSL 3.4. 👑

And deterministic digital signature generation for ECDSA was added to the FIPS provider in OpenSSL 3.6. Deterministic?? In this economy?? Iconic behaviour, truly. 💅

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>.

and that's a wrap on the whole page, bestie!! 🌸 This was PROVIDER-SIGNATURE(7SSL) from OpenSSL 4.0.3, dated 2026-09-29 — go forth and implement your provider signature functions, you absolute queen 👑🦋💖

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