Mental block

Mental block was a rare spell that preserved information against extraction.

Effects
The spell could only affect a willing creature. The creature became incapable of recalling a specific message imparted unto it until conditions selected by the caster were met. Methods such as torture, dispel magic, and other applications of force only caused the complete loss of the message instead.

Per some sources, however, the spell might not have been completely unimpeachable, and mages whose power overwhelmed that of the original caster may have been able to devise methods of cracking this spell.

Components
Besides verbal and somatic components, the spell called for a small block of granite.