W3C home > Mailing lists > Public > public-webcrypto@w3.org > September 2012

Re: JS code examples for ACTION 43

From: Ryan Sleevi <sleevi@google.com>
Date: Wed, 5 Sep 2012 16:58:14 -0700
Message-ID: <CACvaWvbneV+vBy=sBus1NFd-NpR4vEb8iMF0HtP-Q-Aa0mY0uQ@mail.gmail.com>
To: David Dahl <ddahl@mozilla.com>
Cc: "public-webcrypto@w3.org Working Group" <public-webcrypto@w3.org>
On Wed, Sep 5, 2012 at 4:34 PM, David Dahl <ddahl@mozilla.com> wrote:
> Hello everyone:
>
> Arun and I have created a JS example file related to ACTION 43 here: https://github.com/daviddahl/web-crypto-ideas/blob/master/sample-code-fpwd.js
>
> Please send comments when you get a chance. I can incorporate approved examples later this week.
>
> Cheers,
>
> David
>

Individual notes on correctness:
Line 73 - 75:
Why not just call "signer.processData(myData)", since "myData" was
declared at line 32?

Line 121: aesAlgorithm contains AesCbcParams, rather than
AesKeyGenParams (
http://www.w3.org/2012/webcrypto/WebCryptoAPI/#dfn-AesKeyGenParams )

Since you're generating a key (line 129), you should be specifying key
generation params.

var aesKeyGenParams = {
    name: "AES-CBC",
    params: {
        length: 128
    }
};

To encrypt (line 165), you'd need to specify the parameters as you've
done, modulo the concerns below:

Line 124: http://www.w3.org/2012/webcrypto/WebCryptoAPI/#dfn-AesCbcParams
has the IV as an ArrayBufferView, but the sample code uses base64.

Perhaps this should be:
iv: toArrayBufferView(window.atob("NjA....=="))

Line 157: Seems like it should be a Key object.

Line 185: Seems useful to have, especially considering the security of CBC...

Line 203 - 209: Am I mistaken that, by storing into a Uint16Array,
you're effectively adding an extra 0 byte for each ASCII character?
That means that what you're encrypting is not

"53kr3t" but "5\03\0k\0r\03\0t"

That sort of subtlety scares me, since I fear people will copy the
spec as 'good' things. Perhaps this means re-discussing
ArrayBuffer[View] as a data type, or it may mean that the
toArrayBufferView should be "ASCIIToArrayBufferView" or some other
aspect, so that a JS String "53kr3t" is the same as a
C/Python/Ruby/etc string of "53kr3t" which is the same as the literal
data "0x35, 0x33, 0x6b, 0x72, 0x33, 0x74", and NOT "0x35, 0x00, 0x33,
0x00, 0x6b, 0x00, 0x72, 0x00, 0x33, 0x00, 0x74, 0x00"
Received on Wednesday, 5 September 2012 23:58:42 GMT

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