re-implement AsyncStreamCipher buffering

[cfal]

AsyncStreamCipher used to take an &mut self parameter for its encrypt and decrypt functions that would save the iv from the previous block and allow for cfb mode encryption/decryption in a streaming manner: https://docs.rs/cfb-mode/0.7.1/src/cfb_mode/lib.rs.html#79-170

with cfb-mode 0.8.0, encrypt/decrypt now consumes self and no longer supports this.

it would be very helpful for users of cfb-mode 0.7.1 to be able to upgrade to 0.8.0 without having to re-implement this functionality themselves.

thank you!

[saiintbrisson]

I strongly sympathize with this issue as a user of the cfb8 crate. I'm willing to work on a solution, but I'm unsure of what is preferred. Should the functions within AsyncStreamCipher just change back to &mut self (probably a breaking change)? Should a new trait be created?

[tarcieri]

There have been enough reports of issues I’d be in favor of reverting the change in cipher v0.5

[newpavlov]

RustCrypto/block-modes#17 is merged and released, so I think we can close this issue.