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

Re: Need for Smart Card support

From: Wan-Teh Chang <wtc@google.com>
Date: Fri, 8 Jun 2012 11:31:05 -0700
Message-ID: <CALTJjxF4UATEhtBx7pyRiJ9_uAfW==ycoVzWxgqRWRzWoD8SDg@mail.gmail.com>
To: "Davenport, James L." <jdavenpo@mitre.org>
Cc: "public-webcrypto@w3.org" <public-webcrypto@w3.org>
On Mon, Jun 4, 2012 at 7:12 AM, Davenport, James L. <jdavenpo@mitre.org> wrote:
> Our sponsor needs the Crypto API to enable JavaScript programs to be able to
> request: "Hey, please sign this data using that smart card."
> The term "smart card" is a generic term that includes Common Access Card
> (CAC) and Personal Identity Verification (PIV) cards.
> -----------------------------
> Smart Card Use Cases
> -----------------------------
> In all of the following use cases the user must be prompted for his PIN
> prior to signing with the smart card. Also, the system must display to the
> user the data that is being signed, so that he knows what he is signing.
[...Uses cases snipped for brevity...]

Hi Jim,

Thank you for sending the use cases.  Here is a proposal of a signData
function that should support all of your use cases (digitally signing
web transactions).

Please comment on the following issues:
- Is the use of CA names sufficient to identity the right smart card?
- Is supporting just the text/plain media type in the beginning acceptable?


signData Method

The signData method allows JavaScript code to ask the user to digitally sign
a piece of data. If the user approves the operation, signData returns an
encoded JWS signature.


resultString = window.crypto.signData(dataToSign,
                                      [caNameString1, [caNameString2, . . . ]])


    The data you want the user to sign. The data is opaque to the
    signData function. The encoding of text data or canonicalization
    of the date encoding is the responsibility of the application.

    One of the MIME media types registered at IANA
    (http://www.iana.org/assignments/media-types/index.html). The
    browser needs the media type to present dataToSign to the user.

    NOTE: some media types allow comments, annotations, hidden elements
    that may not be visible when presented to the user. The media types
    that are allowed should be restricted.

    An optional summary, in the text/plain media type, of dataToSign.
    plaintextSummary is useful when dataToSign is long or is in a rich
    text media type.

    The signature algorithm, from the list of algorithms in the
    JSON Web Signature (JWS) Internet-Draft (draft-jones-json-web-signature).
    This is mainly used to specify the digest algorithm used in the signature
    because the signing key already constrains the signature algorithms that
    can be used (such as RSA or ECDSA).

    The DN for a CA whose certificates you trust for signing. This is
    used to find the signing certificate and key, which may be on a
    smart card. The use of CA names for specifying an approproate user
    certificate and private key has been used successfully in TLS/SSL
    client authentication.

Return status


    The user canceled the signing operation.

    The signing operation was aborted because the user took too long
    to approve it.

    The user doesn't have a signing certificate and key that meet the

    The signing operation failed.


  On Success, the signData function generates an encoded JWS signature
  as specified in draft-jones-json-web-signature.


  The signData function must present UI for the user to inspect dataToSign
  and the signing certificate and approve the signing operation.

  If the signing key requires the user to enter a PIN before each use,
  that will be handled by the underlying system crypto library. This means
  the PIN dialog might be separate from the signData UI.

  The signData function should work in asynchronous mode because user
  approval can take indefinitely long. This needs more work.

  The signData function as specified is independent of the rest of the
  Web Crypto API.  An alternative design is to break it into two functions:
  - A function to find the appropriate signing certificate and key, given
  - A signData function that takes a certificate handle and private key handle
    as input.

  Displaying a dataMediaType other than text/plain securely is a hard


  The signData function is modeled after the window.crypto.signText function
  in Netscape and Mozilla browsers.

  The plaintextSummary parameter was suggested by Ian Fette.
Received on Friday, 8 June 2012 18:31:34 UTC

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