Re: [Cfrg] [MASSMAIL]Re: Requirements for PAKE schemes

["Stanislav V. Smyshlyaev" <[e-mail]>]

‎Hello, Yoav!

Thank you for your opinion; you are absolutely right that no one needs
trivial considerations like "number of login attempts MUST be controlled"
in each RFC (as much as "users MUST NOT store their passwords on sheets of
paper pinned on their monitors", "Dual EC DRBG MUST NOT be used for
generating both confidential and public data" etc).

Moreover, including such an obvious recommendation is harmful for the
security of implementations. If one reads such a phrase, he'll probably
stop reading "Security considerations" section and won't read really
important info that should be there next: specific recommendations of
handling login attempt counters‎ such as "counter value MUST be incremented
before sending [i]-th message of the [xyz]PAKE protocol".

General recommendations shouldn't be there, but specific ones must.


Kind regards,
Stanislav




2016-01-30 15:15 GMT+03:00 Grigory Marshalko <[e-mail]>:

> It is very important to have such security considerations be written
> somewhere, especially if they are common and obvious for security experts.
> The problem is that for many implementors they are not obvious, and this is
> always the root of flawed implementations.
>
> Regards,
> Grigory Marshalko,
> expert,
> Technical committee for standardisation "Cryptography and security
> mechanisms" (ТC 26)
> www.tc26.ru
>
> 30 января 2016 г., 12:50, "Yoav Nir" <[e-mail]
> <[e-mail]%3E>> написал:
>
>
>
>
> On 29 Jan 2016, at 3:22 PM, Robert Moskowitz <[e-mail]>
> wrote:
>
>
> On 01/29/2016 03:04 AM, Василий Долматов wrote:
>
>
>
> 29 янв. 2016 г., в 9:26, Stanislav V. Smyshlyaev <[e-mail]>
> написал(а):
>
> A major number of cryptography failures follows from incorrect embedding
> of lower-level protocols to high-level ones – if you prove the security of
> PAKE under specific assumtions on counter handling and then someone
> implements it without knowledge of them, you have a practical
> vulnerability. We do not create protocols for vacuum, we make them for
> practice and must write security considerations (a specific "Security
> considerations" section in RFC can be used for discussing these issues, if
> someone thinks that they are not important enough to be in the main part).
>
> I think that idea of moving these recommendations and notice about
> importance of correct setting of these counters to the «Security
> consideration» section is a good one.
>
>
> I agree.  It is the perfect use of "security considerations" for a
> security technlogy.  None of the old "this whole document is about
> security".  The security considerations should contain what the
> risks/threats to the technology is and point out what is done to
> address/mitigate them.
>
>
> I’m not sure about that. These considerations are true for any PAKE. In
> fact, they’re true for any kind of password scheme. You could even make the
> case that they’re true for any authentication scheme, because letting the
> opponent keep guessing is at least creating a DoS on the attacked
> authentication server.
> We generally write in the Security Considerations section stuff that is
> relevant for that particular scheme, not for a whole class of schemes. So
> it may be fine to have a BCP document for “Deploying Password
> Authentication on the Internet”, but I don’t think we need some boilerplate
> text that goes into the security considerations of any password-related RFC.
> Yoav
>
>