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I was looking at using the encrypt option in an application but I've read some comments saying it is not so secure because it uses static keys.

How easy is it to break static key encryption? Does it require lots of data points or just lots of time?

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A static key is one you use more than once over a long period of time. It is often considered less secure than using an ephemeral key (that changes each time) because:

  • An eavesdropper gets more material to work with.
  • If an attacker breaks the key, they can decrypt multiple messages.
  • It gives the attacker the possibility of arranging a known plaintext attack.

However, static keys are often easier to implement. And in some cases none of the above matter. And security is a process, not just using the strongest possible algorithm. (Or else we'd all use one-time pads!)

So the answer is "sometimes more, sometimes less, it depends".

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Also, if there's no nonce at the beginning of the message, an attacker may also be able to compare two messages for equivalence, or (assuming a cipher that is an XOR with keystream), guess the content of two messages and recover the keystream. –  MZB May 3 '12 at 23:17
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If the key is part of the application, it will be very easy for an attacker to use a debugger to extract it. He does not need to break any encryption at all.

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