From the design proposed above, the subsequent step to a detailed design phase and the resulting cost estimates toward implementing the model are relatively straight forward.
Two issues are worth noting. First, in preliminary tests using the MD5-MAC algorithms included in existing in Java and PERL libraries, results were not always consistent or reproducible. This may also be true of other common implementation languages such as Visual Basic, C#, C, C++. In detailing the steps towards implementation, it might be necessary to create a new set of MD5-MAC libraries for all common implementation languages and to distribute these languages to merchant developers and software vendors manufacturing shopping cart software so as to ensure a consistent MAC is generated regardless of the underlying operating platform or implementation language.
Secondly, the Host Message Parser will require some further design work. It is envisioned that this translator will use a number of database tables in constructing the translation algorithm. One will define the acceptable limits or values for a field, another will contain the ordered list of how these values must be sequenced into the host messaging format.