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Re: [dm-devel] [PATCH] crypto/arc4: convert this stream cipher into a block cipher

On Mon, Feb 22, 2010 at 08:45:47AM +0800, Herbert Xu wrote:
> How about this? You extend the IV by one more byte, and use that
> byte as a boolean flag to indicate whether the IV is valid.  All
> users that cannot supply their own IVs can then set the IV to zero.
> When you see the zero flag in the IV, you reinitialise the IV per
> the key.

In fact for arc4 we could just drop the key altogether since it
plays no part after setting the initial state.

> > salsa also does not stick to plan here. ctx->input[6-9] is initialized
> > in encrypt() path. So two threads sharing a ctx are going to clobber
> > their state.
> Salsa should also be fixed.

For Salsa on the other hand the key is rather useful since all
we need is a two-byte IV that's just a sequence number.

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