On Thu, May 27, 2021 at 08:34:51AM -0700, Andres Freund wrote: > Hi, > > On Thu, May 27, 2021, at 08:10, Bruce Momjian wrote: > > On Wed, May 26, 2021 at 05:11:24PM -0700, Andres Freund wrote: > > > Hi, > > > > > > On 2021-05-25 17:12:05 -0400, Bruce Momjian wrote: > > > > If we used a block cipher instead of a streaming one (CTR), this might > > > > not work because the earlier blocks can be based in the output of > > > > later blocks. > > > > > > What made us choose CTR for WAL & data file encryption? I checked the > > > README in the patchset and the wiki page, and neither seem to discuss > > > that. > > > > > > The dangers around nonce reuse, the space overhead of storing the nonce, > > > the fact that single bit changes in the encrypted data don't propagate > > > seem not great? Why aren't we using something like XTS? It has obvious > > > issues as wel, but CTR's weaknesses seem at least as great. And if we > > > want a MAC, then we don't want CTR either. > > > > We chose CTR because it was fast, and we could use the same method for > > WAL, which needs a streaming, not block, cipher. > > The WAL is block oriented too.
Well, AES block mode only does 16-byte blocks, as far as I know, and I assume WAL is more granular than that. Also, you need to know the bytes _before_ the WAL do write a new 16-byte block, so it seems overly complex for our usage too. -- Bruce Momjian <br...@momjian.us> https://momjian.us EDB https://enterprisedb.com If only the physical world exists, free will is an illusion.
