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4 – Encryption Basics for SQL ServerPasswordsIn this day and age the concept of a password is one that is widely understood.These are the strings of characters used to login to computer systems, check oure-mail, activate household security systems and access voicemail messages. InSQL Server, passwords are an option that is available to protect other keyswithin a database. For example, the use of a symmetric key requires it to beopened prior to its reference in cryptographic processes. If a symmetric key isprotected by a password, the string of characters that consists of the protectingpassword must be passed for it to be opened.Passwords are defined with an argument to the key's respective CREATEcommands. Each of the keys covered in this chapter, with the exception of theservice master key, include the ENCRYPTION BY PASSWORD argument intheir creation script examples.An alternative to using passwords to protect the keys within the database is theuse of symmetric keys, asymmetric keys or certificates. Password protectingkeys improve the portability of keys since they are not dependent upon itemsthat are database or instance specific; although, this portability does allow theprotected item to be restored to another instance and compromised to reveal itscontents therefore reducing its level of security.Key MaintenanceCryptographic keys and passwords that protect keys are not a "set-it-andforget-it"feature of securing sensitive data; they require periodic maintenanceto ensure that the items that are protected remain at their highest level ofsecurity. Regular maintenance of keys and passwords reduces the occurrencesof the patterns of encryption being discovered through the monitoring ofencrypted values, a practice called crypto-analysis. It reduces the occurrencesof key fatigue, in which bits of plain text begin to appear among the cipher text.In the unfortunate situation when a key is revealed, improperly disclosed orlost, the scope of the compromised data is reduced if the entire body ofsensitive data is not protected with the same key.This maintenance is handled by shepherding each key through a lifecycle,illustrated in Figure 4-2, which defines when a key is created, used for the firsttime in encryption and decryption, expired for encryption purposes, retiredfrom use and finally eliminated.90