Re: Bug # 24410 - AES CTR descriptions

On Thu, Feb 20, 2014 at 2:04 PM, Jim Schaad <ietf@augustcellars.com> wrote:

> There is a potential missing check that the length of plaintext be less
> than 2^length.  It is easy for people to miss the requirement that all of
> the CTR values be unique.
>

Do you mean that the plaintext length must be less than 2^length blocks
for AES-CTR ? Should this actually be an error, or is it just something we
should recommend ?



>
>
> I realize that the restriction is to be imposed over all uses of the key,
> but is a simple check that could be included.
>
>
>
> **
>
> Do we really want to allow for wrapKey/unwrapKey to be permitted
> operations for AES-CTR mode?  There is no integrity on the key and it's
> value is simple to change.  This could be a potential security attack.  ( I
> note also that the wrap and unwrap functions are not defined, so I assume
> this is a cut and paste error).
>

Presently, wrap / unwrap works for any algorithm that supports encrypt /
decrypt because we have defined wrap = export + encrypt and unwrap =
decrypt + import.

If we wanted to restrict to specific algorithms (which I agree could be a
good idea), then we could define wrap / unwrap operations for the
algorithms that we want to work, so then we would have <warp method> =
<export operation> + <wrap operation> and <unwrap method> = <unwrap
operation> + <import operation>.

That actually seems sensible to me, although it involves duplicating some
text (e.g. for AES-GCM the <unwrap operation> will be identical to the
<decrypt operation>).

...Mark



>
>
>
>
> Jim
>
>
>
>
>
> *From:* Mark Watson [mailto:watsonm@netflix.com]
> *Sent:* Wednesday, February 19, 2014 4:54 PM
> *To:* public-webcrypto@w3.org
> *Subject:* Editors' Draft update
>
>
>
> All,
>
>
>
> I have just updated the Editors' Draft [1] as follows:
>
>
>
> Bug 24410 - operation descriptions for AES CTR:
> https://dvcs.w3.org/hg/webcrypto-api/rev/1d45ba72099d
>
> Bug 24410 - operation descriptions for AES CBC:
> https://dvcs.w3.org/hg/webcrypto-api/rev/50d83a6fae47
>
> Bug 24410 - operation descriptions for AES CFB-8:
> https://dvcs.w3.org/hg/webcrypto-api/rev/f7a0c1209ddf
>
> Bug 24410 - operation descriptions for AES GCM:
> https://dvcs.w3.org/hg/webcrypto-api/rev/1ed0fb7da636
>
> Bug 20611 - specify JWK encoding as UTF-8:
> https://dvcs.w3.org/hg/webcrypto-api/rev/66bec4453de5
>
> Bug 24410 - operation descriptions for AES-CMAC:
> https://dvcs.w3.org/hg/webcrypto-api/rev/768a11dba263
>
> Bug 24410 - operation descriptions for AES-KW and associated method
> updates: https://dvcs.w3.org/hg/webcrypto-api/rev/0fee8e979b4f
>
> Stylistic consistency / correctness for operation descriptions:
> https://dvcs.w3.org/hg/webcrypto-api/rev/fbc6ef272ace
>
>
>
> Please review these changes and send comments to the list.
>
>
>
> Best ... Mark
>
>
>
> [1] https://dvcs.w3.org/hg/webcrypto-api/raw-file/tip/spec/Overview.html
>