B<MD5> is used then the derivation algorithm is compatible with PKCS#5 v1.5
otherwise a non standard extension is used to derive the extra data.
-Newer applications should use more standard algorithms such as PKCS#5
-v2.0 for key derivation.
+Newer applications should use more standard algorithms such as PBKDF2 as
+defined in PKCS#5v2.1 for key derivation.
=head1 KEY DERIVATION ALGORITHM