Re: AES CFB input parameter "s"

I'm inclined to say a over b - outside of 8/128, usage is quite rare.

It was added for the 8 case (GPG, IIRC)
On Feb 14, 2014 5:07 PM, "Mark Watson" <watsonm@netflix.com> wrote:

> Ok, so the options for our specification are:
> (a) choose a fixed value e.g. support only CFB128
> (b) allow the caller to specify the value
> (c) remove the algorithm from the specification
>
> It seems from what you say that it is not the case that everyone supports
> just one value - so there must be applications for the different values.
> So, that would suggest we choose (b) if we don't choose (c).
>
> ...Mark
>
>
> On Fri, Feb 14, 2014 at 3:16 PM, Ryan Sleevi <sleevi@google.com> wrote:
>
>> I haven't heard any implementation movement on CFB.
>>
>> If using PKCS#11, only 8-bit, 64-bit, and 128-bit are defined mechanisms.
>> SP800-38a only provides vectors for 1, 8, 128.
>>
>> AFAICT, CNG supports CFB8 and CFB128 with AES. CFB128 isn't until Win8.
>>
>> OS X only supports CFB8 from what I can tell (at least, via the
>> CommonCrypto interface being used to implement in WebKit)
>> On Feb 14, 2014 3:04 PM, "Mark Watson" <watsonm@netflix.com> wrote:
>>
>>> All,
>>>
>>> Apologies in advance if this has been discussed before, or has a
>>> well-known answer.
>>>
>>> According to NIST SP800-38A [1] Section 6.3 which we reference for AES
>>> CFB, the input parameters to the encrypt/decrypt operations consist of an
>>> IV, the plaintext / ciphertext (respectively) and an additional parameter,
>>> s, which takes a value between 1 and 128, inclusive.
>>>
>>> What values of this shall we support in WebCrypto ?
>>>
>>> I assume that if we wish to support more than one value, then we must
>>> add a property to AesCfbParams for this.
>>>
>>> ...Mark
>>>
>>> [1] http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
>>>
>>
>