NAME

       EVP_SIGNATURE, EVP_SIGNATURE_fetch, EVP_SIGNATURE_free, EVP_SIGNATURE_up_ref,
       EVP_SIGNATURE_is_a, EVP_SIGNATURE_get0_provider, EVP_SIGNATURE_do_all_provided,
       EVP_SIGNATURE_names_do_all, EVP_SIGNATURE_get0_name, EVP_SIGNATURE_get0_description,
       EVP_SIGNATURE_gettable_ctx_params, EVP_SIGNATURE_settable_ctx_params - Functions to manage
       EVP_SIGNATURE algorithm objects

SYNOPSIS

        #include <openssl/evp.h>

        typedef struct evp_signature_st EVP_SIGNATURE;

        EVP_SIGNATURE *EVP_SIGNATURE_fetch(OSSL_LIB_CTX *ctx, const char *algorithm,
                                           const char *properties);
        void EVP_SIGNATURE_free(EVP_SIGNATURE *signature);
        int EVP_SIGNATURE_up_ref(EVP_SIGNATURE *signature);
        const char *EVP_SIGNATURE_get0_name(const EVP_SIGNATURE *signature);
        int EVP_SIGNATURE_is_a(const EVP_SIGNATURE *signature, const char *name);
        OSSL_PROVIDER *EVP_SIGNATURE_get0_provider(const EVP_SIGNATURE *signature);
        void EVP_SIGNATURE_do_all_provided(OSSL_LIB_CTX *libctx,
                                           void (*fn)(EVP_SIGNATURE *signature,
                                                      void *arg),
                                           void *arg);
        int EVP_SIGNATURE_names_do_all(const EVP_SIGNATURE *signature,
                                       void (*fn)(const char *name, void *data),
                                       void *data);
        const char *EVP_SIGNATURE_get0_name(const EVP_SIGNATURE *signature);
        const char *EVP_SIGNATURE_get0_description(const EVP_SIGNATURE *signature);
        const OSSL_PARAM *EVP_SIGNATURE_gettable_ctx_params(const EVP_SIGNATURE *sig);
        const OSSL_PARAM *EVP_SIGNATURE_settable_ctx_params(const EVP_SIGNATURE *sig);

DESCRIPTION

       EVP_SIGNATURE_fetch() fetches the implementation for the given algorithm from any provider
       offering it, within the criteria given by the properties.  The algorithm will be one
       offering functions for performing signature related tasks such as signing and verifying.
       See "ALGORITHM FETCHING" in crypto(7) for further information.

       The returned value must eventually be freed with EVP_SIGNATURE_free().

       EVP_SIGNATURE_free() decrements the reference count for the EVP_SIGNATURE structure.
       Typically this structure will have been obtained from an earlier call to
       EVP_SIGNATURE_fetch(). If the reference count drops to 0 then the structure is freed.

       EVP_SIGNATURE_up_ref() increments the reference count for an EVP_SIGNATURE structure.

       EVP_SIGNATURE_is_a() returns 1 if signature is an implementation of an algorithm that's
       identifiable with name, otherwise 0.

       EVP_SIGNATURE_get0_provider() returns the provider that signature was fetched from.

       EVP_SIGNATURE_do_all_provided() traverses all SIGNATURE implemented by all activated
       providers in the given library context libctx, and for each of the implementations, calls
       the given function fn with the implementation method and the given arg as argument.

       EVP_SIGNATURE_get0_name() returns the algorithm name from the provided implementation for
       the given signature. Note that the signature may have multiple synonyms associated with
       it. In this case the first name from the algorithm definition is returned. Ownership of
       the returned string is retained by the signature object and should not be freed by the
       caller.

       EVP_SIGNATURE_names_do_all() traverses all names for signature, and calls fn with each
       name and data.

       EVP_SIGNATURE_get0_description() returns a description of the signature, meant for display
       and human consumption.  The description is at the discretion of the signature
       implementation.

       EVP_SIGNATURE_gettable_ctx_params() and EVP_SIGNATURE_settable_ctx_params() return a
       constant OSSL_PARAM(3) array that describes the names and types of key parameters that can
       be retrieved or set by a signature algorithm using EVP_PKEY_CTX_get_params(3) and
       EVP_PKEY_CTX_set_params(3).

RETURN VALUES

       EVP_SIGNATURE_fetch() returns a pointer to an EVP_SIGNATURE for success or NULL for
       failure.

       EVP_SIGNATURE_up_ref() returns 1 for success or 0 otherwise.

       EVP_SIGNATURE_names_do_all() returns 1 if the callback was called for all names.  A return
       value of 0 means that the callback was not called for any names.

       EVP_SIGNATURE_gettable_ctx_params() and EVP_SIGNATURE_settable_ctx_params() return a
       constant OSSL_PARAM(3) array or NULL on error.

SEE ALSO

       "ALGORITHM FETCHING" in crypto(7), OSSL_PROVIDER(3)

HISTORY

       The functions described here were added 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>.