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

[Justus Winter <[e-mail]>]

Bruce Walzer <[e-mail]> writes:

> On Sun, Jul 17, 2022 at 09:50:07PM +0200, Justus Winter wrote:
>> Bruce Walzer <[e-mail]> writes:
>> 
>> > At the end of section 5.13.1, at the end of the "NON-NORMATIVE
>> > EXPLANATION" is the following text:
>> >
>> >>However, no update will be needed because the MDC has been replaced
>> >>by the AEAD encryption described in this document.
> [...]
>> Previously, in RFC4880, the paragraph you quoted read:
>> 
>>       However, given the present state of hash function cryptanalysis
>>       and cryptography, it may be desirable to upgrade the MDC system to
>>       a new hash function.  See Section 13.11 in the "IANA
>>       Considerations" for guidance.
>> 
>> Does that clear things up?  Maybe you can suggest some text to make this
>> clearer?
>
> If the text in question ("However, no update will be needed ...") is
> referring to a paragraph that no longer exists in the current
> revision, wouldn't it make the most sense to just delete it too?

The text refers to the paragraph preceding it in the current text, not
to the paragraph in the previous version.  To be explicit, the paragraph
it refers to reads:

   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.)

Justus