Detecting/estimate whether data is encrypted

[chris <chricki () gmx net>]

Hi list,

For the purpose of some research, I'd like to check if (or how likely) a
piece of data is encrypted. I'm particularly interested in analyzing
whether network traffic is encrypted. To make things easier: I don't
mind which algorithm and/or key lengths are used, but just would like
express on a scale from 0% to 100% how likely the data is encrypted.

Some brainstorming led me to the conclusion that measuring the entropy
of data may be a good start. Drawback: there may be false positives,
mostly due to compression).

Any other ideas?

Thanks in advance,
Chris


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