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Re: crypto-ISSUE-13: Relationship between the W3C Web Cryptography work product and the IETF JOSE WG [Web Cryptography API]

From: Wan-Teh Chang <wtc@google.com>
Date: Tue, 21 Aug 2012 13:48:40 -0700
Message-ID: <CALTJjxErPm1ONV1n8r7pM7S7owifTqruNWrhQkoDimRgfCtqeQ@mail.gmail.com>
To: Vijay Bharadwaj <Vijay.Bharadwaj@microsoft.com>
Cc: Ryan Sleevi <sleevi@google.com>, Web Cryptography Working Group <public-webcrypto@w3.org>
On Tue, Aug 14, 2012 at 9:30 AM, Vijay Bharadwaj
<Vijay.Bharadwaj@microsoft.com> wrote:
> Regarding key sizes, I disagree - I think you may have picked the wrong examples for this.
>
> AES-256 is a different algorithm than AES-128; the key expansion is substantially different.
> Similarly, the EC curve is not just a matter of key size; it determines the field in which all
> operations are performed. So I don't think you can have a complete algorithm specification
> without including these two.

Hi Vijay: thank you for your comment. I understand your point. The key size and
elliptic curve name are attributes of a key, and an API can be designed so that
these key attributes determine the variant of the algorithm used. This is the
design used in Java and PKCS #11:
http://java.sun.com/developer/technicalArticles/Security/AES/AES_v1.html
http://bonsai.mozilla.org/cvsblame.cgi?file=mozilla/security/nss/lib/util/pkcs11t.h&rev=1.22&mark=882,884#878
http://bonsai.mozilla.org/cvsblame.cgi?file=mozilla/security/nss/lib/util/pkcs11t.h&rev=1.22&mark=859,861-862#856

I can't quite figure out which design is used in Windows CNG. It seems to be
a mixture because I see BCRYPT_AES_ALGORITHM "AES", which does
not contain the key size, and BCRYPT_ECDSA_P256_ALGORITHM, which
contains the key size/curve name:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa375534%28v=vs.85%29.aspx

Wan-Teh
Received on Tuesday, 21 August 2012 20:49:09 UTC

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