Re: [openpgp] ECC point encoding and "flag byte"

[NIIBE Yutaka <[e-mail]>]

NIIBE Yutaka wrote:
> 4: Ed25519 interoperability issue in GnuPG 2.3-beta (currently being fixed)
> ===========================================================================
>
> In GnuPG 2.3-beta, it is handled as SOS, so, we have an issue for Ed25519.
>
> See:
>
> - Key: https://dev.gnupg.org/T5120
>
> - Signature: https://dev.gnupg.org/T5331

Here are two example files which were produced by GnuPG 2.3-beta.
Those include Ed25519 signatures.

0110.asc includes signature with S part having zero at the start.
0354.asc includes signature with R part having zero at the start.

Here are dumps of these files:

========= 0110.asc ==========
# off=0 ctb=88 tag=2 hlen=2 plen=117
:signature packet: algo 22, keyid E267B052364F028D
	version 4, created 1614755507, md5len 0, sigclass 0x01
	digest algo 10, begin of digest 4f 78
	hashed subpkt 33 len 21 (issuer fpr v4 249CB3771750745D5CDD323CE267B052364F028D)
	hashed subpkt 2 len 4 (sig created 2021-03-03)
	subpkt 16 len 8 (issuer key ID E267B052364F028D)
	data: ADEE890B755C3B52D46FB0105097F23B5905B472C626222ACB4E441D8EB40001
	data: 007119FF80C34DA152BDB07E1EF5D968CB9F2773002A0CF57911670BE248CF06

========= 0354.asc ==========
# off=0 ctb=88 tag=2 hlen=2 plen=117
:signature packet: algo 22, keyid E267B052364F028D
	version 4, created 1614755520, md5len 0, sigclass 0x01
	digest algo 10, begin of digest 28 19
	hashed subpkt 33 len 21 (issuer fpr v4 249CB3771750745D5CDD323CE267B052364F028D)
	hashed subpkt 2 len 4 (sig created 2021-03-03)
	subpkt 16 len 8 (issuer key ID E267B052364F028D)
	data: 001DB3839E3FD8D4CB81357EE5E42F4AF652C252A03A0FB21768621B1025C08C
	data: AF5A0910EF1D4D6BDD07EA0AA6D69049CB7BA7ED42427E14B8B72CF2C2231704


I wonder if other implementations can handle these files correctly.

Specifically, it is malformed MPI in terms of current OpenPGP
specification.
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