1. I have a symmetric key which can be used to encrypt plaintext and decrypt the resulting ciphertext.

  2. I use it to encrypt a plaintext which is a copy of the aforementioned key.

  3. My adversary gets a copy of the resulting ciphertext.

Assuming my adversary knows that the plaintext is a copy of the key, is there a way they can guess my key more easily than if the plaintext wasn't the key?

Note: I am new to cryptography so if there is a flaw in my question I will be happy to clarify.

  • $\begingroup$ Assuming no implementation flaws and your chosen encryption algorithm is well tested and designed, it should not affect how easily the key is guessed. In real life, those assumptions may not necessarily hold though... As with all things cryptography, proceed with caution. $\endgroup$
    – tangrs
    Jun 1 '17 at 3:24
  • $\begingroup$ In that case, do you know of any research on whether this affects real life algorithms? $\endgroup$
    – timotree
    Jun 3 '17 at 2:46
  • 3
    $\begingroup$ You seem to be talking about circular security: blog.cryptographyengineering.com/2012/04/27/… $\endgroup$ Jun 7 '17 at 5:30

There aren't any known generic attacks against this setup to work on arbitrary ciphers. On the other hand, the standard notion of IND-CPA security does not imply security when encrypting your own key.

I don't know of any commonly used block or stream cipher which has trouble with this setup, but one could be created and might even exist.


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