The priest's hand becomes enveloped in a black aura, which when cast requires a to hit of DC12.  A successful hit will negate any protection from good or protection from evil 10' radius without a saving throw, paladins are an exception and are allowed a Wisdom saving throw.

Duration of the spell is 1 round / 2 levels of the caster, for paladins it is increased with a failed saving throw to 2 rounds / level of the priest.