Originally Posted by qtiger
All the messages the hacker has stored use the old key. So it doesn't matter if you change your keys daily, all the hacker has to do it store your encrypted data on his hard drive until he breaks the keys.
DES is the bad idea I was speaking of.
then there would be no point of sending any encrypted message in the first place, because any person could just store the message on his hard drive until he breaks the encryption. in a vast majority of cases, the security of your information is only as secure as your keys/passwords. keep those secure and your system and data will be too. regularly changing passwords and keys is a fundamental security precaution. it's one of the first things you learn in a computer security class when you start learning about encryption and passwords.
DES by itself may not be the best idea, but 3DES is still pretty secure. breaking an encryption key is incredible difficult given almost all modern encryption schemes still in use today (including DES). that's why in the vast majority of cases, hackers attempting to gain access to encrypted information would probably unanimously prefer to just steal a key or a password, NOT break the encryption.