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I know that ECB-mode of block cipher is not recommended to use as it is not secure and is not even EAV-secure. However, I still don't get how to prove that it is not EAV-secure and what adversary is associated with this insecurity? Any help would be appreciated. Thanks in advance. Edited: I found a similar article here: Proving a scheme's EAV-insecurity, and also figured it out. Thank you for all your helps.

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    $\begingroup$ Perhaps a partial duplicate: crypto.stackexchange.com/q/67932 and crypto.stackexchange.com/q/83910 $\endgroup$
    – Patriot
    Jul 25 at 13:29
  • $\begingroup$ Note that EAV secure is indistinguishable encryption against an eavesdropper. It is defined in Katz & Lindells "Introduction to Cryptography", 2nd edition, page 30/31. $\endgroup$
    – Maarten Bodewes
    Jul 25 at 14:58
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    $\begingroup$ Hint, what's the problem with ECB? What happens if both of the messages consist of not one but two blocks? Could you define a pair of messages in such a way that you can show which one was encrypted? $\endgroup$
    – Maarten Bodewes
    Jul 25 at 15:13
  • $\begingroup$ I also see a possible problem with your question, the security is against any adversary $\mathcal{A}$, i.e. you get to play the adversary and define the messages $m_1$ and $m_2$. Although I might be wrong and you are already getting that. $\endgroup$
    – Maarten Bodewes
    Jul 25 at 15:16
  • $\begingroup$ Thank you all for the comments. I figured it out. $\endgroup$
    – Elan613
    Jul 26 at 3:05

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