Re: [openpgp] Wording/meaning (draft-06, 5.13.1)

[Justus Winter <[e-mail]>]

Bruce Walzer <[e-mail]> writes:

> On Wed, Jul 20, 2022 at 10:08:34PM +0200, Justus Winter wrote:
> [...]
>>    Note also that unlike nearly every other OpenPGP subsystem, there are
>>    no parameters in the MDC system. It hard-defines SHA-1 as its hash
>>    function. This is not an accident. It is an intentional choice to
>>    avoid downgrade and cross-grade attacks while making a simple, fast
>>    system. (A downgrade attack would be an attack that replaced SHA2-256
>>    with SHA-1, for example. A cross-grade attack would replace SHA-1 with
>>    another 160-bit hash, such as RIPEMD-160, for example.)
>
> This says that the MDC is immune to downgrade and cross-grade attacks
> because there is only one possible hash (SHA1). What does that have to
> do with updating anything as referred to here:
>
>> However, no update will be needed because the MDC has been replaced
>> by the AEAD encryption described in this document.
>
> ...?

In order to be able to update the system, it would have to be
parameterized in the first place.  The fact that it is not parameterized
is not a problem, because "no update will be needed".  That is the
relation between the two paragraphs.

It has become very clear that the text does not seem to be easy to
understand.  For me, the text seems very clear, but clearly having
worked a long time with the text I have lost that perspective.  Maybe
you can help by proposing a change?

Best,
Justus