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From: Marcel Holtmann <marcel@holtmann.org>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	linux-crypto@vger.kernel.org,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Johannes Berg <johannes@sipsolutions.net>,
	"open list:NFC SUBSYSTEM" <linux-wireless@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [RFC PATCH 0/3] move WEP implementation to skcipher interface
Date: Fri, 7 Jun 2019 22:24:15 +0200
Message-ID: <97BB95F6-4A4C-4984-9EAB-6069E19B4A4F@holtmann.org> (raw)
In-Reply-To: <20190607175947.GB648@sol.localdomain>

Hi Eric,

>> One of the issues that I would like to see addressed in the crypto API
>> is they way the cipher abstraction is used. In general, a cipher should
>> never be used directly, and so it would be much better to clean up the
>> existing uses of ciphers outside of the crypto subsystem itself, so that
>> we can make the cipher abstraction part of the internal API, only to
>> be used by templates or crypto drivers that require them as a callback.
>> 
>> As a first step, this series moves all users of the 'arc4' cipher to
>> the ecb(arc4) skcipher, which happens to be implemented by the same
>> driver, and is already a stream cipher, given that ARC4_BLOCK_SIZE
>> actually evaluates to 1.
>> 
>> Next step would be to switch the users of the 'des' and 'aes' ciphers
>> to other interfaces that are more appropriate, either ecb(...) or a
>> library interface, which may be more appropriate in some cases. In any
>> case, the end result should be that ciphers are no longer used outside
>> of crypto/ and drivers/crypto/
>> 
>> This series is presented as an RFC, since I am mostly interested in
>> discussing the above, but I prefer to do so in the context of actual
>> patches rather than an abstract discussion.
>> 
>> Ard Biesheuvel (3):
>>  net/mac80211: switch to skcipher interface for arc4
>>  lib80211/tkip: switch to skcipher interface for arc4
>>  lib80211/wep: switch to skcipher interface for arc4
>> 
> 
> The way the crypto API exposes ARC4 is definitely broken.  It treats it as a
> block cipher (with a block size of 1 byte...), when it's actually a stream
> cipher.  Also, it violates the API by modifying the key during each encryption.
> 
> Since ARC4 is fast in software and is "legacy" crypto that people shouldn't be
> using, and the users call it on virtual addresses, perhaps we should instead
> remove it from the crypto API and provide a library function arc4_crypt()?  We'd
> lose support for ARC4 in three hardware drivers, but are there real users who
> really are using ARC4 and need those to get acceptable performance?  Note that
> they aren't being used in the cases where the 'cipher' API is currently being
> used, so it would only be the current 'skcipher' users that might matter.
> 
> Someone could theoretically be using "ecb(arc4)" via AF_ALG or dm-crypt, but it
> seems unlikely…

that is not unlikely, we use ecb(arc4) via AF_ALG in iwd. It is what the WiFi standard defines to be used.

Regards

Marcel


  parent reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-07 14:49 Ard Biesheuvel
2019-06-07 14:49 ` [RFC PATCH 1/3] net/mac80211: switch to skcipher interface for arc4 Ard Biesheuvel
2019-06-07 14:49 ` [RFC PATCH 2/3] lib80211/tkip: " Ard Biesheuvel
2019-06-07 14:49 ` [RFC PATCH 3/3] lib80211/wep: " Ard Biesheuvel
2019-06-07 17:59 ` [RFC PATCH 0/3] move WEP implementation to skcipher interface Eric Biggers
2019-06-07 18:08   ` Ard Biesheuvel
2019-06-07 20:24   ` Marcel Holtmann [this message]
2019-06-07 20:27     ` Ard Biesheuvel
2019-06-07 20:45       ` Denis Kenzior
2019-06-07 21:15         ` Eric Biggers
2019-06-07 21:28           ` Denis Kenzior
2019-06-07 21:41             ` Eric Biggers
2019-06-07 21:54               ` Denis Kenzior
2019-06-07 22:40                 ` Eric Biggers
2019-06-07 22:47                   ` Denis Kenzior
2019-06-08 13:03                     ` Sandy Harris
2019-06-08 14:37                       ` Ard Biesheuvel
2019-06-08 15:51                         ` Ard Biesheuvel

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