In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about DES algorithm the authors say that:

"If double encryption is equivalent to single encryption, then the (single encryption) cryptosystem is much less secure than one might guess initially"

The authors don't explain what this means and why. Are you able to tell me ?

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    $\begingroup$ This is the third time you've asked the same question nearly word-for-word. What's going on? $\endgroup$ – Squeamish Ossifrage Oct 17 '19 at 17:53
  • $\begingroup$ It's connected with the other question (that thanks to your help i've understood). But it's another question $\endgroup$ – AleWolf Oct 18 '19 at 13:12
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    $\begingroup$ OK, can you clarify what the difference is, then? $\endgroup$ – Squeamish Ossifrage Oct 18 '19 at 13:38
  • $\begingroup$ This question does appear to be different. The format's the same, including quoting the same source about the same general topic, but this one's asking about a different quote. $\endgroup$ – Nat Oct 19 '19 at 5:17
  • $\begingroup$ @AleQuercia If you give the question a more descriptive title, then it being a non-duplicate would seem more obvious. $\endgroup$ – Nat Oct 19 '19 at 5:20