Thanks for this response.
I guess that's a question of how big a jump Rails 5 is meant to be. I
certainly wouldn't propose this on a minor jump, but I'd figured if you
were rolling from Rails 4 to Rails 5 you could probably deal with sign
outs. I understand the reasons it isn't hugely pressing, but again, if you
were to "upgrade over time", I'd like to consider a major version jump as
the time to do it. Alternatively, there's room to simply look at the length
of a presented hash to check for backward compatibility hashes.
On a related note, why is the CookieStore passed through Base64 encode
twice? Look at a small piece of parsing code I wrote:
str, sign = unescaped_cookie.split(/--/)
# Hex encoded HMAC
puts 'HMAC as per cookie validator: ' + sign
str2 = str.unpack('m').join
cipher, iv = str2.split(/--/)
cipher = c.unpack('m').join
iv = iv.unpack('m').join
What this says is that the Cookiestore is basically formatted as:
B64(B64(iv)--B64(cipher))--hex(HMAC)
I get the feeling that could be much more efficient, both in performance,
and the size of the generated cookies, by skipping that outer encode.
On Wednesday, January 21, 2015 at 6:36:51 AM UTC+11, Michael Koziarski
wrote:
> Switching to another hashing function for Rails 5 would definitely be
> possible. The compatibility concerns are twofold:
>
> * Old hashes are no longer valid, so you sign everyone out the day you do
> that deploy
> * Various old rubies on old OSes ship with old OpenSSL which didn't
> support it.
>
> That second concern is well and truly gone these days so there's no reason
> to worry about it. However the first concern remains. You'd have to offer
> a transitional system where it accepted sha1 hashes and returned sha256
> ones. You'd also need to think carefully about the defaults because if you
> accept the sha1 hashes forever you're never actually closing the
> theoretical issues. It's not particularly difficult just requires time and
> effort.
>
> Finally, the issues you're raising around sha1 don't necessarily apply
> when used in an HMAC as it is here. We should definitely upgrade over
> time, but it's not as pressing as the TLS certs case.
>
> On Tue Jan 20 2015 at 7:12:03 PM <jsma...@gmail.com <javascript:>> wrote:
>
>> Hi,
>>
>> I note that Cookiestore signs its data using SHA-1.
>>
>> I have found this issue regarding this:
>> https://github.com/rails/rails/pull/11677
>>
>> There it was noted that documentation was updated from SHA512, which
>> would appear to have been considered at one time, to using SHA1 "for
>> compatibility". SHA-1 is considered a deprecated cryptographic hash. The
>> deprecation of support for SHA-1 certificates by Google in the Chrome
>> browser is an example of proactive deprecation of obsolete algorithms that
>> is generally well accepted by the community. The long term lifespan of a
>> Cookiestore session cookie, coupled with the sensitivity of the session
>> data often stored within it should be considered to amplify the threat.
>>
>> I was wondering what "compatibility" issues would be present in changing
>> the default hash to SHA-256 for an upcoming rails 5. It's been supported in
>> OpenSSL for a very long time, which is in turn used to generate this hash.
>> The documentation update was over a year ago, and that only documented an
>> earlier configuration change which I don't believe to reflect current
>> security practice.
>>
>> Moreover, that particular PR discusses this as not being configurable.
>> I've spent some time trying to get a gem to override it without much
>> success.
>>
>> Any assistance on towards making this a default, or on how it could be
>> turned into a gem would be appreciated.
>>
>>
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