Subpacket 33 and GnuPG Specifics on RFC-4880 Tag ID's, algorithm identifiers, etc

Werner Koch wk at
Thu Jan 25 09:13:28 CET 2018

On Thu, 25 Jan 2018 05:43, gnupg-users at said:
> After looking at the content of subpacket 33, it appears to be the signing-key's fingerprint prepended by '0x04'.
> So I'm guessing subpacket 33 is to be a more robust version of subpacket 16 (Issuer)?

Right.  From RFC-4880bis (draft -03)

|  {} Issuer
|    (8-octet Key ID)
|    The OpenPGP Key ID of the key issuing the signature.  If the version
|    of that key is greater than 4, this subpacket MUST NOT be included in
|    the signature.
|  Issuer Fingerprint
|    (1 octet key version number, N octets of fingerprint)
|    The OpenPGP Key fingerprint of the key issuing the signature.  This
|    subpacket SHOULD be included in all signatures.  If the version of
|    the issuing key is 4 and an Issuer subpacket is also included in the
|    signature, the key ID of the Issuer subpacket MUST match the low 64
|    bits of the fingerprint.
|    Note that the length N of the fingerprint for a version 4 key is 20
|    octets; for a version 5 key N is 32.

Note that the OpenPGP WG page is not anymore updated automatically, thus
you better watch

for updates.  I use 


to prepare new draft versions.  With gpg implementing some propose
changes I guess I should do a -04 soonish.  I will report also to
gnupg-devel whne tehre is a new draft.



Die Gedanken sind frei.  Ausnahmen regelt ein Bundesgesetz.
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