Data encryption performs two purposes: it protects data against internal prying eyes, and it protects data against external threats (hacking, theft of backup tapes, etc.) Encryption in the database tier offers the advantage of database-caliber performance and protection of encryption keys without incurring the overhead and additional cost of using a third-party encryption tool in an application tier.
To read Garbus’ complete article which explores best practices and design considerations in column-level encryption as practiced with Sybase Adaptive Server Enterprise 15 (ASE 15), go here.