6.5. Practical issues with encryption

If encryption is so good, why not use it everywhere? Are there any guidelines on where to use it? Are there any drawbacks in using it? Encryption poses interesting choices and questions such as what to encrypt, how to encrypt, and what kind of tools we should use.

Ideally you would like to encrypt every bit of information, but that certainly has drawbacks. For example, if we encrypt all the credit card transactions, including the total amount to be paid, we may not able to write applications that can audit or generate alerts based on the amount. Moreover, sometimes it may be legally necessary for us to leave some of the information in clear text.