Common examples of application fields resorting to embedded solutions are cryptography, access control, smart cards, automotive, avionics, space, entertainment, and electronic sales outlets. In order to illustrate the main steps of the design process, a small digital signature system will now be developed (complete assembly language and VHDL code available).
The system under development (Figure 1.1) has three inputs,
and two outputs,
The working of the system is shown in Figure 1.2: a sequence c1, c2, … , cn of any number n of characters (the message), synchronized by the signal new_character, is inputted. When the sign control signal goes high, the done flag is lowered and the signature of the message is computed. The done flag will be raised as soon as the signature s is available.
In order to sign the message two functions must be defined: