EVP_PKEY_get_default_digest_nid, EVP_PKEY_get_default_digest_name - get default signature digest

       Copyright 2006-2023 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>.

3.5.0                                              2025-06-04              EVP_PKEY_GET_DEFAULT_DIGEST_NID(3SSL)

EVP_PKEY_get_default_digest_name() fills in the default message digest name for the public key signature
       operations associated with key pkey into mdname, up to at most mdname_sz bytes including the ending NUL
       byte.  The name could be "UNDEF", signifying that a digest must (for return value 2) or may (for return
       value 1) be left unspecified.

       EVP_PKEY_get_default_digest_nid() sets pnid to the default message digest NID for the public key
       signature operations associated with key pkey.  Note that some signature algorithms (i.e. Ed25519 and
       Ed448) do not use a digest during signing.  In this case pnid will be set to NID_undef.  This function is
       only reliable for legacy keys, which are keys with a EVP_PKEY_ASN1_METHOD; these keys have typically been
       loaded from engines, or created with EVP_PKEY_assign_RSA(3) or similar.

       This function was added in OpenSSL 1.0.0.

       EVP_PKEY_get_default_digest_nid, EVP_PKEY_get_default_digest_name - get default signature digest

       For all current standard OpenSSL public key algorithms SHA256 is returned.

EVP_PKEY_get_default_digest_name() and EVP_PKEY_get_default_digest_nid() both return 1 if the message
       digest is advisory (that is other digests can be used) and 2 if it is mandatory (other digests can not be
       used).  They return 0 or a negative value for failure.  In particular a return value of -2 indicates the
       operation is not supported by the public key algorithm.

EVP_PKEY_CTX_new(3), EVP_PKEY_sign(3), EVP_PKEY_digestsign_supports_digest(3), EVP_PKEY_verify(3),
       EVP_PKEY_verify_recover(3),

        #include <openssl/evp.h>

        int EVP_PKEY_get_default_digest_name(EVP_PKEY *pkey,
                                             char *mdname, size_t mdname_sz);
        int EVP_PKEY_get_default_digest_nid(EVP_PKEY *pkey, int *pnid);