using methods base64 module in conjunction with Crypto.Hash.SHA256

[Klaas]

mirandacascade at yahoo.com wrote:
> I am attempting to implement a process, and I'm pretty sure that a
> major roadblock is that I do not understand the nomenclature.  The
> specs indicate that the goal is to calculate a message digest using an
> SHA-256 algorithm.  There are 2 examples included with the specs.  The
> label on the 2 examples are: 'HMAC samples'.  In both examples, the
> message on which the digest is to be calculated is (the 33 chars within
> the quotes):
>
> 'This is a test of VISION services'
>
> In the first example, the value labeled 'Shared key' is the 44
> characters within the quotes:
>     '6lfg2JWdrIR4qkejML0e3YtN4XevHvqowDCDu6XQEFc='

I doubt it.  That is a base64 encoded value, not the value itself.

<>
> My interpretation of the first example is this: when you use an SHA-256
> algorithm to calculate a message digest on the message 'This is a test
> of VISION services' where the key is
> '6lfg2JWdrIR4qkejML0e3YtN4XevHvqowDCDu6XQEFc=',

This isn't the key, but the base64-encoded key.

> the result should be:
> 'KF7GkfXkgXFNOgeRud58Oqx2equmKACAwzqQHZnZx9A=' .

This isn't the result, but the base64-encoded result.

> 2) If the interpretation of the first example is on target, do you see
> anything above in the use of the SHA256, HMAC and base64
> classes/methods that indicates that I did not correctly implement the
> process?

You should base64 decode the key before passing it to the HMAC
constructor.

-Mike