Field-level encryption is the ability to encrypt data in specific data fields.
Examples of fields that can be encrypted are credit card numbers, social security numbers, bank account numbers, health-related information, wages and financial data. Once a field is chosen, all the data in that field will automatically be encrypted. Encryption can be done using either secret or public keys. A secret key uses a single key to both encrypt and decrypt messages. Therefore it must be present at both the source and the destination of transmission. It also must be kept secret by all parties. A public key system uses a pair of keys that can decrypt messages encrypted by the other.
It is advised that companies avoid field-level encryption on existing databases and instead build it into new systems with sensitive data.