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Re: [Sks-devel] dealing with misplaced signatures

 

 

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dkg at fifthhorseman

Jul 31, 2012, 3:53 PM

Post #1 of 2 (149 views)
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Re: [Sks-devel] dealing with misplaced signatures

On 07/31/2012 06:04 PM, Kristian Fiskerstrand wrote:
> Currently we have a patch[0] ready that allows for these signatures to
> be cleaned in the getting (and vindex) of the key,

A patch with the stated functionality would be a Good Thing.

> However, before creating a Pull Request into the SKS Trunk, we have to
> verify that this solution would not actually violating RFC4880.

If anything, the current sks implementation is violating RFC 4880, which
clearly states that transferable public key certificates contain:

- After each Subkey packet, one Signature packet, plus optionally a
revocation

SKS seems willing to record and produce more than one signature packet
in this position. The "one signature packet" is unambiguously intended
to refer to a subkey binding signature, fwiw, not any of the other
signature types.

Note that i think it's probably reasonable for sks to store more than
one subkey binding signature packet per subkey (to accomodate subkey
expiration revisions, particularly since sks has no cryptographic
verification in place, so it can't tell a valid subkey expiration
revision from an invalid one); i'm not arguing for blind adherence to
the spec, i'm arguing for practical utility here.

> Although
> there are implications that 0x10-0x13 signatures are for UID/UAT
> packages, and as such would not belong to a subkey, would starting to
> "hide information" be a violation of SKS's neutral way of storing data,

sks should not be so neutral as to store incomprehensible data (we
reject malformed packets, for example), and no one has stepped forward
with any explanation of why an identity certification signature could
make sense following a subkey.

Pursuing the patch to sks will fix one part of the problem here; gpg
probably also needs fixing to drop these bogus packets, or at least to
reassign them to their correct spot in the certificate if such a spot
can be found. Note also that the same signature packet might be
duplicated; if it fits in one place in the keyring, and a byte-for-byte
identical signature packet is found elsewhere, in a place where it is
not cryptographically valid, that latter copy of the packet can probably
be safely discarded.

my $0.02,

--dkg
Attachments: signature.asc (1.01 KB)


kristian.fiskerstrand at sumptuouscapital

Jul 31, 2012, 4:16 PM

Post #2 of 2 (140 views)
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Re: [Sks-devel] dealing with misplaced signatures [In reply to]

On 2012-08-01 00:53, Daniel Kahn Gillmor wrote:
> On 07/31/2012 06:04 PM, Kristian Fiskerstrand wrote:

...

>
> If anything, the current sks implementation is violating RFC 4880, which
> clearly states that transferable public key certificates contain:
>
> - After each Subkey packet, one Signature packet, plus optionally a
> revocation
>

Hi Daniel,

What complicate it a bit is that an argument can be made that this, from
11.1 [0], "The essential elements of a transferable public key are as
follows:" is a non-exhaustive list, i.e. it is more of a minimum
requirement than a full spec (by the use of the word "essential").

[0] http://www.ietf.org/rfc/rfc4880.txt

--
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