Re: [openpgp] Issuer Fingerprint

Werner Koch <wk@gnupg.org> Tue, 14 June 2016 18:01 UTC

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From: Werner Koch <wk@gnupg.org>
To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
References: <87mvmp5rmi.fsf@wheatstone.g10code.de> <87y46720pc.fsf@alice.fifthhorseman.net>
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Subject: Re: [openpgp] Issuer Fingerprint
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Hi,

here is another try with dkg's suggestions:

--8<---------------cut here---------------start------------->8---
@@ -1055,6 +1055,7 @@ #### {5.2.3.1} Signature Subpacket Specification
           30   Features
           31   Signature Target
           32   Embedded Signature
+          33   Issuer Fingerprint
   100 to 110   Private or experimental
 
 An implementation SHOULD ignore any subpacket of a type that it does
@@ -1155,7 +1156,9 @@ #### {5.2.3.5} Issuer
 
 (8-octet Key ID)
 
-The OpenPGP Key ID of the key issuing the signature.
+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.
 
 #### {5.2.3.6} Key Expiration Time
 
@@ -1615,6 +1618,19 @@ #### {5.2.3.26} Embedded Signature
 in Section 5.2 above.  It is useful when one signature needs to refer
 to, or be incorporated in, another 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.
+
 ### {5.2.4} Computing Signatures
 
 All signatures are formed by producing a hash over the signature data,
--8<---------------cut here---------------end--------------->8---


Salam-Shalom,

   Werner

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