Develop trait for tweakable block ciphers

[rustcrypto]

Develop trait for tweakable block ciphers

[eternaleye]

One thing worth noting is that tweak changes aren't necessarily free (some constructions even use tweak-dependent keys for the underlying block cipher), and an interface that can amortize this may be beneficial.

EDIT: Optimally Secure Tweakable Blockciphers may be of interest; it shows tweakable block cipher constructions that can break the birthday bound, though they make use of tweak-dependent keys.

EDIT 2: Even in LRW2, the construction works as Ẽ(k, t, m) = E(k, m ^ h(t)) ^ h(t) - precomputing h(t) may have nontrivial benefit.

[WildCryptoFox]

For HCTR the TBC trait would need to recognize Variable Input Lengths and variable tweaks (depending on the AXU it is instantiated with).

I don't think GenericArray can currently capture variable lengths.

[newpavlov]

I will close it in favor of RustCrypto/traits#177.