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



On Sun, Mar 14, 2010 at 09:24:32AM +0100, Sebastian Andrzej Siewior wrote:
> 
> Okay. So so are we talking about something like that below then? This is

Pretty much.

> untested and I break other users bexcept lib80211_crypt_tkip. 

For the sake of compatibility please do this as a 3-step dance.
First add a new arc4 blkcipher, then convert the users, and
finally delete the old arc4.

>  static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
>  			unsigned int key_len)
>  {
> -	struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
> +	/*
> +	 * ARC4 is special: The user should supply an IV as struct arc4_iv and
> +	 * fill either the key or the iv.
> +	 */
> +	return -EOPNOTSUPP;
> +}

You should return 0 here.  You should also set the min/max key
size to zero.  The new arc4 no longer has a key as far as the
API is concerned.

Cheers,
-- 
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