I am looking at using a third party key distribution protocol. I do not have much details of the internals itself. However I am required to configure the time for regeneration of the (128 bit symmetric keys used for encryption. Are there any standard mechanism to determine that. I understand that regeneration will be depend on the volume of data / or time duration so that we reduce the chances of an attacker capturing and breaking the key. But I could not find more details after searching the internet. Thanks for any answers

  • renew after each "logical" unit. At least re-new every day so at most the data of one day is lost. 128-bit keys are considered secure until 2050. – SEJPM May 24 '15 at 16:35

No, there aren't any standard formulas. The reason for that is that e.g. an AES-128 key may be used for very large amounts of data. Modes of encryption, protocol requirements and requirements on the data itself however do pose limits and those limits are usually much lower than the one for the symmetric cipher.

Say that you could use an AES key to encrypt 2^48 blocks in CBC mode. In that case you could encrypt 2^52 bytes or 4.503.599.627.370.496 bytes or about 4.5 peta byte if I'm not mistaken. And that's for CBC mode, the block cipher itself should have higher limits.

So the question is more how much separation you require between the protected blobs of data.

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