A paladin of tyranny must be of lawful evil alignment and loses all class abilities if he ever willingly commits a good act. Additionally, a paladin of tyranny's code requires that he respect authority figures as long as they have the strength to rule over the weak, act with discipline (not engaging in random slaughter, keeping firm control over those beneath his station, and so forth), help only those who help him maintain or improve his status, and punish those who challenge authority (unless, of course, such challengers prove more worthy to hold that authority).
Yep, it's in the SRD right there.