I hope that this is not a duplicate because I'm looking for nuance. I understand the difference between ECB and CBC for a block cipher, and I understand that ECB is susceptible to replay attacks, but my question is just from the standpoint of strength. If I have cipher that has 256-bit key and 128-bit data that is used to encrypt a file on a disk, the mathematical complexity does not increase between CBC and ECB for cracking the cipher? I read a lot of answers saying "ECB is insecure", but there's a difference in theory and practice. I expect to only have 1k 128-bit blocks.
I have an extremely power constrained system, and I'm trying to determine if the 10% overhead required for CBC over a ECB architecture matters from the standpoint of security. The reason is that if I do have a significant gain using CBC over ECB, perhaps I should just use a smaller cipher size because I'd basically be trading up circuits.
Any suggestions from the engineering perspective would be appreciated.