Re: [openpgp] Question on computing v5 signatures

[Werner Koch <[e-mail]>]

Hello!

On Wed,  1 May 2019 21:29, [e-mail] said:
> I am wondering why a number of eight-octet size is used here. The
> biggest field, AFAIS i.e. the hashed subpacket data area, is limited
> by the included two-octet hashed subpacket length. So why 64 bit?

That seems to be a misunderstanding.  The original patch from Brian
(9b846b7e from 2017-02-13) had this text:

  V5 signatures instead hash in a ten-octet trailer: the version of the
  Signature packet, i.e., 0x05; 0xFF; and an eight-octet, big-endian
  number that is the length of the hashed data from the Signature packet
  (note that this number does not include these final ten octets).

He might have extended the counter to eight octets to better distinguish
a V5 signature form a V4 signature.  Reading this I falsely concluded
that the 32 bit counter of a V4 signature might overflow and thus added

  The four-octet big-endian number is considered to be an unsigned
  integer modulo 2^32.

to the V4 signature desciption.  Obviously we both missed that a 32 bit
counter is sufficient for a a max of 2*2^16+something octets.


Shalom-Salam,

   Werner

-- 
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