v3 consent to attribute release : attribute hash function ?

[Tom Zeller]

On Mon, Sep 8, 2014 at 11:28 AM, Ian Young <ian at iay.org.uk> wrote:
>
> On 8 Sep 2014, at 17:09, Tom Zeller <tzeller at dragonacea.biz> wrote:
>
>> When calculating the hash of attribute values used to determine if any
>> values have changed since consent was last granted, should v3 use the
>> DataSealer ? Maybe that's overkill for client-side storage since the
>> DataSealer will be used again on the cookie. Currently, uApprove hex
>> encodes the SHA-256 message digest of the concatenated values of an
>> attribute. If the DataSealer should not be used in v3, it seems
>> GZIP'ing and Base64 encoding, like the DataSealer does, would reduce
>> storage size.
>
> Base64 encoding would be smaller than hex encoding, but I don't understand what you're saying about compression. Compressing the input of the hash won't change the size of the output, and you can't compress the output of the hash prior to encoding, that would just make it bigger on average.

I was looking at lines 235 - 247 of the DataSealer, where it uses a
GZIPOutputStream as part of generating the plaintext, and was thinking
that would make the hash smaller, but, duh, no.