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Cryptography

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  • $\begingroup$ Does having an attacker know only "which blocks have changed" necessarily imply vulnerability to known or chosen plaintext attacks? $\endgroup$ Commented Nov 4, 2020 at 3:26
  • $\begingroup$ It's more information than the attacker would get otherwise. In some cases this can be enough information for the attacker to get what they need, in other cases it can be completely harmless. $\endgroup$ Commented Nov 4, 2020 at 11:14
  • $\begingroup$ Interesting -- it sounds like it might depend on the "threat or attack model" that one might be trying to defend against too. $\endgroup$ Commented Nov 4, 2020 at 13:04
  • $\begingroup$ On a side note -- is the OP's cipher scheme essentially the same as merely doing $C_i = E_K(P_i \oplus (IV + i))$ but with an identical IV for every "version" of some file? Different files can have different IV's, but every 'version' of the same file gets encrypted (and overwritten) using the same IV as it had before. $\endgroup$ Commented Nov 4, 2020 at 13:27
  • $\begingroup$ @ManRow almost, it's $C_i = E_K(P_i \oplus E_K(IV + i))$. And the reuse of the IV is just what this question is about. $\endgroup$ Commented Nov 4, 2020 at 14:14