Is it possible to decrypt this?

Question

PHP

<? eval(gzuncompress(base64_decode('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'))); ?>

How to encrypt so that it is not easily decrypted?

Answer 1

Do not confuse encoding and encryption. There is nothing encrypted in your example. There is a string encoded in base64 and compressed with gzip.
If you want to encrypt specifically, you have a wide choice (see the list at the bottom of the page).

Answer 2

replace eval with echo/print and voila.

Answer 3

Throw the salt again, you can run base64(string+salt) several times in the loop and, for example, throw the occurrence of the salt into the string in different places for fun.