RE: getLength

Does getLength need to be in the key_ops list in JWA or should it not be?  I think the answer is that it should not be, but I wanted to ask.

As far as I can tell, there’s only one use of the string “getLength” in the current editor’s draft, which is confusing, because it’s not defined.

                                                            -- Mike

From: Mark Watson [mailto:watsonm@netflix.com]
Sent: Monday, October 20, 2014 11:32 AM
To: Mike Jones
Cc: public-webcrypto@w3.org
Subject: Re: getLength

Hi Mike,

"operations" supported by the various WebCrypto algorithms are *not* the same as the "methods" supported by the crypto.subtle interface.

Each method has an associated procedure which, amongst other things, calls out to one or more of the operations supported by the algorithms.

For example, the encrypt method does various pieces of work before calling the encrypt operation.

The deriveKey method calls out to three operations, first the getLength operation of the derived key algorithm then the deriveBits operation of the key derivation algorithm and finally the import operation of the derived key algorithm

getLength is needed because the number of bits to generate depends on interpretation of the Algorithm object for the *derived* key (the target). This interpretation can only be done by the algorithm, not entirely within the method, so we need an operation to do that.

I have argued several times that we should have a clearer distinction between operation and method names, to avoid this confusion, which keeps coming up again and again. But so far *no one* has supported or even commented on my suggestions.

...Mark

On Mon, Oct 20, 2014 at 11:24 AM, Mike Jones <Michael.Jones@microsoft.com<mailto:Michael.Jones@microsoft.com>> wrote:
What is the getLength operation in https://dvcs.w3.org/hg/webcrypto-api/raw-file/tip/spec/Overview.html#algorithm-concepts-operations?  And why is this list different than the list at https://dvcs.w3.org/hg/webcrypto-api/raw-file/tip/spec/Overview.html#subtlecrypto-interface-methods, which doesn’t include it?

                                                            -- Mike