EVP_PKEY_get_default_digest() manual page.

doc/crypto/EVP_PKEY_get_default_digest.pod

+=pod
+
+=head1 NAME
+
+EVP_PKEY_get_default_digest_nid - get default signature digest
+
+=head1 SYNOPSIS
+
+ #include <openssl/evp.h>
+ int EVP_PKEY_get_default_digest_nid(EVP_PKEY *pkey, int *pnid);
+
+=head1 DESCRIPTION
+
+The EVP_PKEY_get_default_digest_nid() function sets B<pnid> to the default
+message digest NID for the public key signature operations associated with key
+B<pkey>.
+
+=head1 NOTES
+
+For all current standard OpenSSL public key algorithms SHA1 is returned.
+
+=head1 RETURN VALUES
+
+The EVP_PKEY_get_default_digest_nid() function returns 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).  It returns 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.
+
+=head1 SEE ALSO
+
+L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>,
+L<EVP_PKEY_sign(3)|EVP_PKEY_sign(3)>,
+L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>,
+L<EVP_PKEY_verifyrecover(3)|EVP_PKEY_verifyrecover(3)>,
+
+=head1 HISTORY
+
+This function was first added to OpenSSL 0.9.9.
+
+=cut