Added encryption key cannot indefinitely using, has following has several reasons: key key using time more long, it leaked of opportunities on more big; if key key has leaked, so key key using more long, loss on more big; key key using more long, people spent energy decipher it of temptation force on more big--even used poor lift attack method; on with same key key encryption of multiple redaction for password analysis General compared easy.
Different key should have a different validity period.
Mainly depends on the validity of the data key value of the data and the number of encrypted data in the given time. The value used by the data transfer rate increases key replacement more frequently.
Key the encryption key without frequent change, because they are only occasionally used for key exchange. In some applications, the key encryption key in January alone, or replaced once a year.
The encryption key used to encrypt data files used to transform. Usually each file is encrypted with a unique key, then the key encryption key to encrypt all key encryption key or memory, or stored in a secure location. Of course, the files that are missing this key means the loss of all encryption keys.
Private key in public-key password is valid varies according to the different applications. Private key used for digital signatures and identity must be continued for several years (or even life) used as a thrown coin Protocol private key should be destroyed immediately after the completion of the agreement. Even though expectations the key security last a lifetime, change the key two years must also be a consideration. Old keys remain confidential, in case the user needs to verify the signature. But the new key signature will be used as the new file to reduce the cryptanalyst can attack signature file number.