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.