- NAME
- SYNOPSIS
- DESCRIPTION
  - Context Management Functions
  - Signing Functions
  - Verify Functions
  - Verify Recover Functions
  - Digest Sign Functions
  - Digest Verify Functions
  - Signature parameters
  - MD parameters
- RETURN VALUES
- SEE ALSO
- HISTORY
- COPYRIGHT

# NAME

provider-signature - The signature library <-> provider functions

# 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);

    /* 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);

    /* 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);

    /* 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

This documentation is primarily aimed at provider authors. See provider(7) for further information.

The signature (OSSL_OP_SIGNATURE) operation enables providers to 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).

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)).

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_sign_init              OSSL_FUNC_SIGNATURE_SIGN_INIT
    OSSL_FUNC_signature_sign                   OSSL_FUNC_SIGNATURE_SIGN

    OSSL_FUNC_signature_verify_init            OSSL_FUNC_SIGNATURE_VERIFY_INIT
    OSSL_FUNC_signature_verify                 OSSL_FUNC_SIGNATURE_VERIFY

    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. In order 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:

OSSL_FUNC_signature_sign_init and OSSL_FUNC_signature_sign
OSSL_FUNC_signature_verify_init and OSSL_FUNC_signature_verify
OSSL_FUNC_signature_verify_recover_init and OSSL_FUNC_signature_verify_recover
OSSL_FUNC_signature_digest_sign_init, OSSL_FUNC_signature_digest_sign_update and OSSL_FUNC_signature_digest_sign_final
OSSL_FUNC_signature_digest_verify_init, OSSL_FUNC_signature_digest_verify_update and OSSL_FUNC_signature_digest_verify_final
OSSL_FUNC_signature_digest_sign_init and OSSL_FUNC_signature_digest_sign
OSSL_FUNC_signature_digest_verify_init and OSSL_FUNC_signature_digest_verify

OSSL_FUNC_signature_set_ctx_params and OSSL_FUNC_signature_settable_ctx_params are optional, but if one of them is present then the other one must also be present. The same applies to OSSL_FUNC_signature_get_ctx_params and OSSL_FUNC_signature_gettable_ctx_params, as well as the "md_params" functions. The OSSL_FUNC_signature_dupctx function is optional.

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.

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.

## 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.

## 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_digeset_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() finalises a signature operation previously started through OSSL_FUNC_signature_digest_sign_init() and OSSL_FUNC_signature_digest_sign_update() calls. Once finalised no more data will be added through OSSL_FUNC_signature_digest_sign_update(). A previously initialised signature context is passed in the ctx parameter. 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.

OSSL_FUNC_signature_digest_sign() implements a "one shot" digest sign operation previously started through OSSL_FUNC_signature_digeset_sign_init(). A previously initialised signature context is passed in the ctx parameter. 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 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.

## Digest Verify Functions

OSSL_FUNC_signature_digeset_verify_init() initialises a context for verifying given a provider side verification 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 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_verify_update() provides data to be verified in the data parameter which should be of length datalen. A previously initialised verification context is passed in the ctx parameter. This function may be called multiple times to cumulatively add data to be verified.

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 the ctx parameter. 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_digeset_verify_init(). A previously initialised verification context is passed in the ctx parameter. 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.

OSSL_FUNC_signature_get_ctx_params() gets signature parameters associated with the given provider side signature context ctx and stored 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.

"digest" (OSSL_SIGNATURE_PARAM_DIGEST) <UTF8 string>

  Get 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.

"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 that corresponds to the combination of signature algorithm and digest algorithm for the signature operation.

"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.

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.

Parameters currently recognised by built-in signature algorithms are the same as those for built-in digest algorithms. See "Digest Parameters" in provider-digest(7) for further information.

OSSL_FUNC_signature_gettable_md_ctx_params() and OSSL_FUNC_signature_settable_md_ctx_params() get a constant OSSL_PARAM(3) array that describes the gettable and settable digest parameters, i.e. parameters that can be used with OSSL_FUNC_signature_get_md_ctx_params() and OSSL_FUNC_signature_set_md_ctx_params() respectively.

# RETURN VALUES

OSSL_FUNC_signature_newctx() and OSSL_FUNC_signature_dupctx() should return the newly created provider side signature context, or NULL on failure.

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 in a constant OSSL_PARAM(3) array.

All other functions should return 1 for success or 0 on error.

# SEE ALSO

provider(7)

# HISTORY

The provider SIGNATURE interface was introduced in OpenSSL 3.0.

# COPYRIGHT

Copyright 2019-2023 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.