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Re: Support for ECB

From: David McGrew (mcgrew) <mcgrew@cisco.com>
Date: Mon, 10 Sep 2012 16:53:27 +0000
To: Wan-Teh Chang <wtc@google.com>, "public-webcrypto@w3.org" <public-webcrypto@w3.org>
Message-ID: <CC739131.D1C40%mcgrew@cisco.com>
Hi Wan-Teh,

On 9/5/12 6:03 PM, "Wan-Teh Chang" <wtc@google.com> wrote:

>Ryan already summarized my reactions to this proposal in his email,
>but it seems useful for me to state them for official record.
>
>1. The design of the Web Crypto API shows a desire to promote good
>crypto practices. Exposing the ECB mode runs counter to this design
>philosophy.
>
>2. One reason we're considering providing the ECB mode is the
>difficulty of specifying the CTR mode parameters that support every
>counter incrementing function. I think the CTR mode parameters
>specified in the draft are sufficient in practice. Does anyone know of
>a protocol that puts the block counter in the high-order bits?

I don't know of any standards that do counter mode that way.  It seems
that most have an "increment" function that does addition in the low-order
16 or 32 bits, and assumes big endian integer representation.   This
certainly goes for the IETF protocols (though they do IVs in different
ways).


David

>Using
>LFSR to increment the block counter is attractive to hardware
>implementations, but seems awkward for software.
>
>In summary, I would not object to exposing the ECB mode, but I don't
>see a strong need for it. In particular, exposing the ECB mode should
>not be our way to avoid specifying the CTR mode.
>
>Wan-Teh
>
Received on Monday, 10 September 2012 17:01:05 GMT

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