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Prove that ECB-mode of a block cipher is not EAV-secure

vn flag

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.

Patriot avatar
cn flag
Perhaps a partial duplicate: https://crypto.stackexchange.com/q/67932/ and https://crypto.stackexchange.com/q/83910/
Maarten Bodewes avatar
in flag
Note that EAV secure is indistinguishable encryption against an eavesdropper. It is defined in Katz & Lindells "Introduction to Cryptography", 2nd edition, page 30/31.
Maarten Bodewes avatar
in flag
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?
Maarten Bodewes avatar
in flag
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.
Elan613 avatar
vn flag
Thank you all for the comments. I figured it out.
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