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Re: [openpgp] Question on computing v5 signatures

"Neal H. Walfield" <neal@walfield.org> Thu, 02 May 2019 06:35 UTC

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Date: Thu, 02 May 2019 08:35:42 +0200
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From: "Neal H. Walfield" <neal@walfield.org>
To: Heiko Stamer <HeikoStamer@gmx.net>
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Subject: Re: [openpgp] Question on computing v5 signatures
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Hi Heiko,

On Wed, 01 May 2019 21:29:09 +0200,
Heiko Stamer wrote:
> regarding compution of v5 signatures we have the following lines
> in section 5.2.4 of the current draft RFC 4880bis-06:
> 
>   "a eight-octet big-endian number that is the length of the
>    hashed data from the Signature packet stopping right before the
>    0x05, 0xff octets."
> 
> I am wondering why a number of eight-octet size is used here. The
> biggest field

I don't know about this.

> , AFAIS i.e. the hashed subpacket data area, is limited
> by the included two-octet hashed subpacket length. So why 64 bit?

Actually, the MPIs can be larger.  They take up the remainder of the
packet.  In practice, the MPIs are just a few kilobytes today, but
with post-quantum crypto, they could get very large.

:) Neal

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