L<EVP_DigestInit_ex(3)>, L<EVP_DigestUpdate(3)> and L<EVP_DigestFinal_ex(3)>.
Digest implementations may be obtained in one of three ways, i.e. implicit
-lookup, explicit lookup or user defined.
+fetch, explicit fetch or user defined.
=over 4
-=item Implicit Lookup
+=item Implicit Fetch
-With implicit lookup an application can use functions such as L<EVP_sha256(3)>,
+With implicit fetch an application can use functions such as L<EVP_sha256(3)>,
L<EVP_sha512(3)> or L<EVP_blake2b512(3)> to obtain an B<EVP_MD> object. When
used in a function like L<EVP_DigestInit_ex(3)> the actual implementation to
be used will be fetched implicitly using default search criteria. Typically,
have been loaded), this will return an implementation of the appropriate
algorithm from the default provider.
-=item Explicit Lookup
+=item Explicit Fetch
-With explicit lookup an application uses the EVP_MD_fetch() function to obtain
+With explicit fetch an application uses the EVP_MD_fetch() function to obtain
an algorithm implementation. An implementation with the given name and
satisfying the search criteria specified in the B<properties> parameter will be
looked for within the available providers and returned. See L<OSSL_PROVIDER(3)>
L<EVP_MD_meth_free(3)>. Note that EVP_MD objects are reference counted. See
L<EVP_MD_upref(3)>.
+=head1 NOTES
+
+Where an application that previously used implicit fetch is converted to use
+explicit fetch care should be taken with the L<EVP_MD_CTX_md(3)> function.
+Specifically, this function returns the EVP_MD object orginally passed to
+EVP_DigestInit_ex() (or other similar function). With implicit fetch the
+returned EVP_MD object is guaranteed to be available throughout the application
+lifetime. However, with explicit fetch EVP_MD objects are reference counted.
+EVP_MD_CTX_md does not increment the reference count and so the returned EVP_MD
+object may not be accessible beyond the lifetime of the EVP_MD_CTX it is
+associated with.
+
=head1 RETURN VALUES
EVP_MD_fetch() returns a pointer to the algorithm implementation represented by