Re: Reusing signed user ID or attribute
Thank you Daniel, it actually sounds very right. Now that I think about it, storing this kind of data in the public key block isn't so good afterall. I will investigate over this and ask to the right ML next time. Thank you everyone for your help. On Sun, Jan 19, 2014 at 5:21 PM, Daniel Kahn Gillmor wrote: > On 01/19/2014 09:55 AM, Daniele Ricci wrote: >> Ok, so I have to conclude it's implementation specific? >> I'm using a custom user attribute to store something that can change >> quite often (privacy lists for a chat user). What do you suggest? > > I don't know what a "privacy list for a chat user" is. You should > probably try to document what you are trying to achieve more clearly, > and present it in a public forum where people can help you think through > possible ways to achieve it. > > This thread started off by asking about user IDs or attributes, which > seems to assume that this is the only way to provide the information > you're looking for. But an OpenPGP notation (stored within the > self-signature) could also provide that information directly. > > User IDs and User Attributes are for information that you need or want > third parties to confirm and certify. Information in an OpenPGP > notation does *not* need to be confirmed or certified by third parties. > So if Alice wants to indicate something about her preferences about how > to use chat, she can do so in a notation subpacket within her self-sig. > > does this make sense? > > --dkg > > -- Daniele ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Reusing signed user ID or attribute
On 01/19/2014 09:55 AM, Daniele Ricci wrote: > Ok, so I have to conclude it's implementation specific? > I'm using a custom user attribute to store something that can change > quite often (privacy lists for a chat user). What do you suggest? I don't know what a "privacy list for a chat user" is. You should probably try to document what you are trying to achieve more clearly, and present it in a public forum where people can help you think through possible ways to achieve it. This thread started off by asking about user IDs or attributes, which seems to assume that this is the only way to provide the information you're looking for. But an OpenPGP notation (stored within the self-signature) could also provide that information directly. User IDs and User Attributes are for information that you need or want third parties to confirm and certify. Information in an OpenPGP notation does *not* need to be confirmed or certified by third parties. So if Alice wants to indicate something about her preferences about how to use chat, she can do so in a notation subpacket within her self-sig. does this make sense? --dkg signature.asc Description: OpenPGP digital signature ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Reusing signed user ID or attribute
Am So 19.01.2014, 15:55:51 schrieb Daniele Ricci: > Ok, so I have to conclude it's implementation specific? > I'm using a custom user attribute to store something that can change > quite often (privacy lists for a chat user). What do you suggest? My first thought is: Why should it make sense to put this data into a certificate? Use a simple file with a simple signature. Let the signature expire every few days (or hours, whatever you need). You may put the URL of the file into the certificate using a notation. Hauke -- Crypto für alle: http://www.openpgp-schulungen.de/fuer/unterstuetzer/ http://userbase.kde.org/Concepts/OpenPGP_Help_Spread OpenPGP: 7D82 FB9F D25A 2CE4 5241 6C37 BF4B 8EEF 1A57 1DF5 signature.asc Description: This is a digitally signed message part. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Reusing signed user ID or attribute
Ok, so I have to conclude it's implementation specific? I'm using a custom user attribute to store something that can change quite often (privacy lists for a chat user). What do you suggest? On Fri, Jan 17, 2014 at 1:28 PM, Hauke Laging wrote: > Am Fr 17.01.2014, 11:44:55 schrieb Daniele Ricci: > >> My question is the following: suppose I create a user ID or attribute. >> I sign it with my key and that's ok. >> One day I revoke that user ID or attribute and sign it again with a >> certification revocation. >> >> A few years later, I want to restore that user ID or attribute >> because, e.g. I restored an old e-mail address. Is it enough to sign >> the revoked user attribute once again with a valid signature (then >> timestamps will do the rest) or do I have to create a new user ID with >> the same data? > > I am afraid that depends on the implementation. The RfC isn't clear on > that (if I understand it correctly). > > It says about self-signatures (a revocation is not a self-signature in > this sense, though): > > "An implementation that encounters multiple self-signatures on the same > object may resolve the ambiguity in any way it sees fit, but it is > RECOMMENDED that priority be given to the most recent self-signature." > > About revocations it says: > > "0x30: Certification revocation signature >This signature revokes an earlier User ID certification signature >(signature class 0x10 through 0x13) or direct-key signature >(0x1F). It should be issued by the same key that issued the >revoked signature or an authorized revocation key. The signature >is computed over the same data as the certificate that it >revokes, and should have a later creation date than that >certificate." > > IIRC then GnuPG accepts a later self-signature (overriding the > revocation). IMHO that makes most sense. As long as the mainkey isn't > revoked or expired why shouldn't one "change one's mind"? > > I haven't tried now but IIRC you have to delete the revocation first > before you can create a new signature. > > > Hauke > -- > Crypto für alle: http://www.openpgp-schulungen.de/fuer/unterstuetzer/ > http://userbase.kde.org/Concepts/OpenPGP_Help_Spread > OpenPGP: 7D82 FB9F D25A 2CE4 5241 6C37 BF4B 8EEF 1A57 1DF5 -- Daniele ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Reusing signed user ID or attribute
On Friday 17 January 2014 14:33:25 Daniel Kahn Gillmor wrote: > I think you're conflating revocation of the primary key with revocation > of a user ID. > > Revocation of a primary key is permanent and cannot be overridden. > Revocation of a user ID can be overridden as long as the primary key > (the one making the certification) is not itself revoked. Ah, yes, I was indeed thinking of the primary key. Thanks for clearing that up! Cheers, Johannes signature.asc Description: This is a digitally signed message part. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Reusing signed user ID or attribute
Am Fr 17.01.2014, 20:03:15 schrieb Johannes Zarl: > If, however, the revocation is only a temporary act until a newer > self- signature supersedes it, it would be almost impossible to > effectively and permanently revoke a key. That's why we all use only the super-secure (haha) offline mainkeys. Hauke -- Crypto für alle: http://www.openpgp-schulungen.de/fuer/unterstuetzer/ http://userbase.kde.org/Concepts/OpenPGP_Help_Spread OpenPGP: 7D82 FB9F D25A 2CE4 5241 6C37 BF4B 8EEF 1A57 1DF5 signature.asc Description: This is a digitally signed message part. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Reusing signed user ID or attribute
On 01/17/2014 02:03 PM, Johannes Zarl wrote: > If the revocation is a final act, as long as I can make sure that the > revocation certificate reaches my communication partners I can be sure that > nobody can compromise the key and "reenable" it and start impersonating me. > > If, however, the revocation is only a temporary act until a newer self- > signature supersedes it, it would be almost impossible to effectively and > permanently revoke a key. One would either (as long as the private key is not > yet compromised) have to destroy the private key, or make sure that all > communication partners somehow prevent the key from receiving further > updates... I think you're conflating revocation of the primary key with revocation of a user ID. Revocation of a primary key is permanent and cannot be overridden. Revocation of a user ID can be overridden as long as the primary key (the one making the certification) is not itself revoked. --dkg signature.asc Description: OpenPGP digital signature ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Reusing signed user ID or attribute
On Friday 17 January 2014 13:28:50 Hauke Laging wrote: > IIRC then GnuPG accepts a later self-signature (overriding the > revocation). IMHO that makes most sense. As long as the mainkey isn't > revoked or expired why shouldn't one "change one's mind"? Wouldn't that have huge implications for the security(*) of the whole system? If the revocation is a final act, as long as I can make sure that the revocation certificate reaches my communication partners I can be sure that nobody can compromise the key and "reenable" it and start impersonating me. If, however, the revocation is only a temporary act until a newer self- signature supersedes it, it would be almost impossible to effectively and permanently revoke a key. One would either (as long as the private key is not yet compromised) have to destroy the private key, or make sure that all communication partners somehow prevent the key from receiving further updates... Johannes (*) please excuse the blanket-use of the term signature.asc Description: This is a digitally signed message part. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Re: Reusing signed user ID or attribute
Am Fr 17.01.2014, 11:44:55 schrieb Daniele Ricci: > My question is the following: suppose I create a user ID or attribute. > I sign it with my key and that's ok. > One day I revoke that user ID or attribute and sign it again with a > certification revocation. > > A few years later, I want to restore that user ID or attribute > because, e.g. I restored an old e-mail address. Is it enough to sign > the revoked user attribute once again with a valid signature (then > timestamps will do the rest) or do I have to create a new user ID with > the same data? I am afraid that depends on the implementation. The RfC isn't clear on that (if I understand it correctly). It says about self-signatures (a revocation is not a self-signature in this sense, though): "An implementation that encounters multiple self-signatures on the same object may resolve the ambiguity in any way it sees fit, but it is RECOMMENDED that priority be given to the most recent self-signature." About revocations it says: "0x30: Certification revocation signature This signature revokes an earlier User ID certification signature (signature class 0x10 through 0x13) or direct-key signature (0x1F). It should be issued by the same key that issued the revoked signature or an authorized revocation key. The signature is computed over the same data as the certificate that it revokes, and should have a later creation date than that certificate." IIRC then GnuPG accepts a later self-signature (overriding the revocation). IMHO that makes most sense. As long as the mainkey isn't revoked or expired why shouldn't one "change one's mind"? I haven't tried now but IIRC you have to delete the revocation first before you can create a new signature. Hauke -- Crypto für alle: http://www.openpgp-schulungen.de/fuer/unterstuetzer/ http://userbase.kde.org/Concepts/OpenPGP_Help_Spread OpenPGP: 7D82 FB9F D25A 2CE4 5241 6C37 BF4B 8EEF 1A57 1DF5 signature.asc Description: This is a digitally signed message part. ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
Reusing signed user ID or attribute
Hello list, I'm manipulating PGP keys with Bouncy Castle, especially signatures of user IDs and user attributes. But my question is not about development, it's about signatures. My question is the following: suppose I create a user ID or attribute. I sign it with my key and that's ok. One day I revoke that user ID or attribute and sign it again with a certification revocation. A few years later, I want to restore that user ID or attribute because, e.g. I restored an old e-mail address. Is it enough to sign the revoked user attribute once again with a valid signature (then timestamps will do the rest) or do I have to create a new user ID with the same data? Thanks -- Daniele ___ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
