RE: Online Certificate Revocation Protocol
Santosh Chokhani <chokhani@cygnacom.com> Thu, 14 June 2001 16:37 UTC
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From: Santosh Chokhani <chokhani@cygnacom.com>
To: "Scherling, Mark" <mscherling@rsasecurity.com>, 'jim' <jimhei@cablespeed.com>, Santosh Chokhani <chokhani@cygnacom.com>
Cc: thayes@netscape.com, Ietf-Pkix <ietf-pkix@imc.org>
Subject: RE: Online Certificate Revocation Protocol
Date: Thu, 14 Jun 2001 11:41:46 -0400
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I think we may agree on the philosophy. But, some of your words are confusing and misleading to me. 1. The private key is not being kept active as your words can be interpreted. The public key certificate continues to be valid. 2. I agree with you that would leave it up to the PKI and its CP and CPS as to what to do with respect to the destroyed private keys. 3. Since my sentiments are that destroyed keys pose minimal threat (one of discovering the key), we should not make a recommendation or provide a preferred approach if the private key is destroyed. If we do provide a recommendation, it should be that in most scenarios let the sleeping dogs lie, i.e., do NOT revoke the certificate. -----Original Message----- From: Scherling, Mark [mailto:mscherling@rsasecurity.com] Sent: Thursday, June 14, 2001 11:45 AM To: 'jim'; Santosh Chokhani Cc: Scherling, Mark; thayes@netscape.com; Ietf-Pkix Subject: RE: Online Certificate Revocation Protocol Without dragging this out longer, the choice is with the CA and what they define in their policies and procedures (CP and CPS). Technically a destroyed key can be kept indefinitely. From a business or security perspective, it is the choice of the CA and the organization (the PKI Management Authority would get a report or I hope that the CA would report this and the PKI Management Authority would accept the risk of keeping the destroyed key active otherwise they would request it be revoked). Would you agree Santosh? -----Original Message----- From: jim [mailto:jimhei@cablespeed.com] Sent: Thursday, June 14, 2001 4:43 AM To: Santosh Chokhani Cc: Scherling, Mark; thayes@netscape.com; Ietf-Pkix Subject: Re: Online Certificate Revocation Protocol Comments in line... Santosh Chokhani wrote: Jim:Please see comments in-line. -----Original Message----- From: jim [ mailto:jimhei@cablespeed.com <mailto:jimhei@cablespeed.com> ] Sent: Wednesday, June 13, 2001 10:10 AM To: Santosh Chokhani Cc: Scherling, Mark; thayes@netscape.com; Ietf-Pkix Subject: Re: Online Certificate Revocation Protocol I have to jump in again. Mark is correct. Remember that we are talking a Certification Revocation List (CRL). This is vastly different than a Compromised Key List (CKL). We place a certificate on the CRL because there is a larger problem other than just the signing key. If the token set is damaged or destroyed (this is a good place to insert Bob's reflection on bent keys), the cert needs to be added to the CRL. If there is some way to ensure that only a keyset is damaged, the cert can be rekeyed so that service for the DN continues. It specifically does come back to the concern of knowing what is considered destroyed and what is considered bent. Since I have not seen the equivalent of a CKL in the IETF world, I have to assume that the only way to truly cancel usage of a key is either to put the cert on the CRL or to rekey the cert so that the old key is no longer valid. The question becomes how to demonstrate that a key has been invalidated without invalidating the DN or cert. [Santosh Chokhani] Why do you want to claim a destroyed key is invalid? I do not want to claim that a destroyed key is invalid. What I believe needs to happen is recognition that the CA is the one to make the decision as to whether the key is destroyed, not the user. If, for instance, I am using a system with a hard token, if the key is run over by a car and will not be usable, there is still the remains of the key to be turned over to the CA and the CA can make the decision. If the key is a software token, there is no such manner of determining that the key is truly destroyed by the average PKI user. As such, why allow a user to determine whether the key is destroyed? All I think needs to happen is recognize that this is a CA decision and let the CA take the appropriate precautions in accordance with the CP/CPS for the system. As you know a subscriber or an authority will stop using a private key well before the expiration of public key certificate used for signature verification. But, absent trusted time stamp, PKIX does NOT recommend use of private key validity period. So, just because key is not usable any more, you should revoke it. Besides if the subject is a CA and issued numerous certificates, revoking CA's key will cause unneeded Denial of Service. BTW, even if you had trusted time stamp or notary, unless get certificates notarized, revoking CA's public key certificate will either cause denial of service or will not protect against a security breach. Here is the scenario. If the you put the CA on the revoked list, all the certificates issued have been invalidated for no reason. If you apply the logic that you will use "invalidity date" CRL: extension and match against the certificate issuance time (let us say notBefore date), if the key was truly in wrong hands, they will issue bogus certificates with pre-dated notBefore date. I think Santosh and I agree that the question is one of trust as to whether the key is truly destroyed as opposed to being unusable to the user, [Santosh Chokhani] I am not sure we agree. I think certificate need not be revoked if the key is destroyed. Now if the CA stops trusting the holder of the private key, that is a different matter. Again, here is the decision point. Does the CA make the trust decision? I think so, and if that is the case, the CA should be endowed with the final decision as to whether the key is destroyed, not the user. This takes us back to Bob J.'s question about bent keys, which I totally agree with. Again, it needs to be a CA decision in accordance with a CP/CPS. but the issuing authority still has the responsibility for making that determination and if needed, revoking the cert to invalidate the key. There is a fine line between what happens technically and what needs to happen procedurally. Thus, I still side with Mark and the proponents of transaction notarization (accomplishable through a retrievable audit trail) as a better, more secure process. [Santosh Chokhani] I do not care buy that PKI is useless with trusted time or notary service. Useless no, but risk mitigation of possible court action is critical in business depending on the value of the transaction and criticality of the information being passed, so there is reason to have at a minimum an audit trail that no only indicates the computer event that takes place, but also what data or transfer of funds occurred with that transaction. Whether this is done by timestamping and notarization or with the persistent proof audit log offered by Conclusive Logic, Inc., is a matter for each enterprise to decide, but we as technologists need to let that be a business decision, not try to make it for them by saying, "You don't need to do it, so we won't include the capability." PKI systems need to be designed to support the enterprise business model and the security managers at an enterprise define the CP/CPS for that system with all of their security issues being invoked. Thus, it makes sense for the CA responsible for issuing authenticatable certificates to users to cover the types of transactions the business wants to perform to be the single decision maker in enforcing CP/CPS policy and procedures in the case of determining whether a key is truly destroyed. Most users do not have that capability and the burden should not be put on them. Those users who do have that capability should be more capable of accurately reporting to the CA that the key was truly destroyed. Then the CA, working with the Security Manager, can make the appropriate decision that implements the policies and procedures that were designed for the system. Obviation of the security policies and procedures reduces the secure nature of the PKI, which is why it was originally implemented. If we reduce the secureness that is offered by the PKI, we certainly reduce the PKI market. I am not arguing about what needs to happen as far as the technical capability of key management, but from the risk mitigation standpoint, which is what business needs to deal with. They need to have an electronic system that is as inherently secure as their paper system or PKI will never get off the ground. Jim Santosh Chokhani wrote: Please see responses in-line. -----Original Message----- From: Scherling, Mark [ mailto:mscherling@rsasecurity.com <mailto:mscherling@rsasecurity.com> ] Sent: Tuesday, June 12, 2001 4:30 PM To: 'Santosh Chokhani'; Scherling, Mark; thayes@netscape.com Cc: Ietf-Pkix Subject: RE: Online Certificate Revocation Protocol Hi Santosh, I'm not sure why you would think that revoking a certificate would result in a denial of service? If your key has been destroyed and I want to use your public key to send you a message, you cannot read it. I will assume you have received the message since there is no other indication (CRL or OCSP response). Unless you tell me otherwise and then I may think that you are denying receipt of my messages. I'm assuming that we have an agreement that the messages we are sending are confidential and sensitive and require encryption and signing. [Santosh Chokhani] If some thing has been signed and subsequently the private key is destroyed, the public key can still be used to verify the signature, if the key was not revoked. I do not want to get into the time stamp protocol since I want a PKI to function to some degree without "trusted time stamp". Now, imagine that an intermediate CA key is destroyed. There is no need to revoke the CA key and invalidate all the certificates issued by the CA. I realize that the CA can generate a new key and re-issue all the certificates, but this work need not be done. In short, the denial of services comes from revoking a certificate that is perfectly fine.I also don't understand why you would not want to revoke a key if it was destroyed? [Santosh Chokhani] I do not understand what the need to revoke the certificate is?If I cannot use my key to sign or decrypt or gain access to a service then what is the value of that key to me? [Santosh Chokhani] You are right in the decryption scenario, but as stated earlier not right in the signature scenario. If a key is revoked, it is placed on a CRL until the key expires. The key can no longer be used for signing [Santosh Chokhani] But what about what was signed before, unless you integrate trusted time stamp and revamp the X.509 and PKIX path validation to account for time and trusted time, legitimate signatures will be rejected. and as Bob pointed out others cannot use the public key to encrypt messages to the key holder.In my experience, most users forget their pass phrase (be it userid and password or key and pass phrase). If the user destroys their key at this point, what is the purpose of keeping the key? Why would you not revoke the key?Sorry to burden you but could you explain to me why you think revoking a certificate is a denial of service? -----Original Message----- From: Santosh Chokhani [ mailto:chokhani@cygnacom.com <mailto:chokhani@cygnacom.com> ] Sent: Tuesday, June 12, 2001 12:56 PM To: Scherling, Mark; Santosh Chokhani; thayes@netscape.com Cc: Ietf-Pkix Subject: RE: Online Certificate Revocation Protocol Mark:I think if the certificate issuing authority trusts that the subject key is truly destroyed, I have not seen any cogent argument on this list yet for revoking the certificate. All I hear is:1. It is safe thing to do.2. Well we can use trusted time stamp or notary to get around the denial of serviceI see no particular reason for revocation in the case of a destroyed key. Bob Juneman ha made the most cogent point that for private decryption key, if there is no key recovery, you may want to revoke so that others do not use the public key since the subject can not use the private key.Rest of the discussion is NOT related to key being destroyed, but related to not trusting the key being destroyed, not trusting the subject, or trying to over-design the PKI.I will give you one thing, it is always safe to revoke any key, if you do not care about denial of service. -----Original Message----- From: Scherling, Mark [ mailto:mscherling@rsasecurity.com <mailto:mscherling@rsasecurity.com> ] Sent: Tuesday, June 12, 2001 3:31 PM To: 'Santosh Chokhani'; thayes@netscape.com; Scherling, Mark Cc: Ietf-Pkix Subject: RE: Online Certificate Revocation Protocol Sorry bad example in that leaving an organization should automatically trigger a revocation of your certificate. But, if you are an administrator and you know that the key was destroyed and had other pressing things, you may be tempted to forget despite the fact that it states that in your policies and procedures. Is it not true that human error is the cause in most security breaches?Then let me paint you another scenario, the VP gives his secretary (never happens :-) her keys and access to her e-mail and accounts to handle routine correspondence. If the VP 's key is accidentally destroyed, is there another copy? Who has access to it? If the VP stays and the secretary leaves, is there a security risk? I guess I'm just a little to paranoid.Cheers -----Original Message----- From: Santosh Chokhani [ mailto:chokhani@cygnacom.com <mailto:chokhani@cygnacom.com> ] Sent: Tuesday, June 12, 2001 11:57 AM To: thayes@netscape.com; Scherling Mark Cc: Ietf-Pkix Subject: RE: Online Certificate Revocation Protocol I agree with "thayes". -----Original Message----- From: thayes@netscape.com [ mailto:thayes@netscape.com <mailto:thayes@netscape.com> ] Sent: Tuesday, June 12, 2001 2:50 PM To: Scherling Mark Cc: Ietf-Pkix Subject: Re: Online Certificate Revocation Protocol Mark, In this message you use the phrases "after I left the organization" and "someone leaves the company". This tells me that your affiliation has changed, and therefore any certificate you hold indicating that affiliation should be revoked. This has nothing to do with whether the key has been destroyed. Using the destruction of the key as a replacement for revocation is not a good idea for the reasons you give. However, I see no requirement to revoke a certificate for a destroyed key if the subject is otherwise in good standing. Terry Scherling, Mark wrote: >The problem is that today we have no way of determining what "hold" means. >We can suspend a certificate which means it's not available, but my >preference is to revoke a certificate if the private key is in an unknown >state, that is we think it was destroyed but there is no way of determining >if that is absolutely true. > >If you look at a lot of the cyber-thefts, a large percentage was with >insider knowledge. It would be easy to say my key has been destroyed and >then use my key for access to something after I left the organization. You >would have proof that the key was destroyed (I signed a piece of paper >saying so, with date and time, witnessed by my VP, etc.) yet the key was >used to gain access after the date and time. It's not a matter of trust, >but a matter of risk management. If my key was unknowingly compromised and >then destroyed, the key is still valid unless we revoke the key. It is far >safer than assuming that the key was destroyed. > >In the case of a CA key, I would rather revoke all keys and re-issue than >take the risk that the CA key was destroyed and no other copies exist. > >So we want to restrict the ability to use the key even if it has been >destroyed because we cannot with absolution determine that the key was >destroyed and no copies exist. In many Subscriber Agreements and >Certificate Policies, it states that the Subscriber may back up their keys >using proper safeguards as long as they are the only ones with access. In >the event that someone leaves a company and their private key was destroyed >prior to them leaving, the back up key may be in a sealed envelope with the >passphrase at their desk or in their filing cabinet. I know that most of us >would never do this sort of thing but many people do. So now you are left >with a key that has not been revoked and is still active. Would we all not >consider this a security risk? > >The bottom line is that if a private key is in an unknown state, the CA >should revoke the key. > >-----Original Message----- >From: Carlin Covey [ mailto:ccovey@cylink.com <mailto:ccovey@cylink.com> ] >Sent: Tuesday, June 12, 2001 9:07 AM >To: Paul Gogarty; Lynn.Wheeler@firstdata.com; mscherling@rsasecurity.com >Cc: Ietf-Pkix >Subject: RE: Online Certificate Revocation Protocol > > >Placing the certificate on hold and using some sort of hold instruction code >makes sense to me. But the hold instruction code would have to refer to >some date after which new signatures are considered invalid. That >presupposes a timestamp on the signed document, so there is a trusted >signature time to compare with the the "no new signatures after ..." time in >the hold code. Of course, we could use the private key usage extension to >specify the time, if the CA, RA or subject of the signature certificate >knows this time when the certificate is issued. In an earlier posting Lynn >Wheeler noted that in such a case the CA/RA functions might be combined with >the timestamping notary function. > >Mark, is this similar to what you had in mind when you mentioned revoking >the private key? That is, we want restrictions placed on validation of >signatures made with the private key based upon when the signatures were >created. > >Regards, > >Carlin > >____________________________ > >- Carlin Covey > Cylink Corporation > >-----Original Message----- >From: owner-ietf-pkix@mail.imc.org >[ mailto:owner-ietf-pkix@mail.imc.org <mailto:owner-ietf-pkix@mail.imc.org> ]On Behalf Of Paul Gogarty >Sent: Tuesday, June 12, 2001 8:11 AM >To: Ietf-Pkix >Subject: RE: Online Certificate Revocation Protocol > > > >In cases where keys are destroyed before their revocation date would it not >make more sense to place the certificate on hold (use a combination of >'Reason Code' and 'Hold Instruction Code' CRL entry extensions). > >This allows the certificate to validate as part of a certification path or >for signature verification, but provides a date after which signatures from >the certificate should not be trusted and the encryption key should not be >used. > > Paul Gogarty > ASN.1 Developer > > De La Rue InterClear Ltd. > De La Rue House > Jays Close > Viables > Basingstoke > England > RG22 4BS > > Fax: +44 (0)1256 487755 > Tel: +44 (0)7879 458416 > mailto:paul.gogarty@interclear.co.uk <mailto:paul.gogarty@interclear.co.uk> > > http://www.interclear.co.uk/ <http://www.interclear.co.uk/> >
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- Re: Online Certificate Revocation Protocol Hansen Wang
- RE: Online Certificate Revocation Protocol Carlin Covey
- RE: Online Certificate Revocation Protocol Peter Williams
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- RE: Online Certificate Revocation Protocol Santosh Chokhani
- Re: Online Certificate Revocation Protocol Tony Bartoletti
- Re: Online Certificate Revocation Protocol Tony Bartoletti
- RE: Online Certificate Revocation Protocol Santosh Chokhani
- Re: Online Certificate Revocation Protocol Andrew W. Gray
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- Re: Online Certificate Revocation Protocol Tony Bartoletti
- Re: Online Certificate Revocation Protocol Tony Bartoletti
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- Re: Online Certificate Revocation Protocol jim
- Re: Online Certificate Revocation Protocol Hansen Wang
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- Re: Online Certificate Revocation Protocol Massimiliano Pala
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- RE: Online Certificate Revocation Protocol Santosh Chokhani
- RE: Online Certificate Revocation Protocol Santosh Chokhani
- Re: Online Certificate Revocation Protocol Paul Hoffman / IMC
- Re: Online Certificate Revocation Protocol jim
- Re: Online Certificate Revocation Protocol Peter Gutmann
- Re: Online Certificate Revocation Protocol Peter Gutmann
- Re: Online Certificate Revocation Protocol Peter Gutmann
- RE: Online Certificate Revocation Protocol Santosh Chokhani
- Re: Online Certificate Revocation Protocol Massimiliano Pala
- Re: Online Certificate Revocation Protocol Bob Jueneman
- RE: Online Certificate Revocation Protocol Santosh Chokhani
- RE: Online Certificate Revocation Protocol Santosh Chokhani
- RE: Online Certificate Revocation Protocol Carlin Covey
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- RE: Online Certificate Revocation Protocol Tony Bartoletti
- Re: Online Certificate Revocation Protocol Tony Bartoletti
- Re: Online Certificate Revocation Protocol Marc Branchaud
- Re: Online Certificate Revocation Protocol Marc Branchaud
- RE: Online Certificate Revocation Protocol Santosh Chokhani
- Re: Online Certificate Revocation Protocol Massimiliano Pala
- RE: Online Certificate Revocation Protocol Lynn.Wheeler
- Re: Online Certificate Revocation Protocol Marc Branchaud
- RE: Online Certificate Revocation Protocol Carlin Covey
- RE: Online Certificate Revocation Protocol Lynn.Wheeler
- RE: Online Certificate Revocation Protocol Paul Gogarty
- RE: Online Certificate Revocation Protocol Scherling, Mark
- RE: Online Certificate Revocation Protocol Carlin Covey
- RE: Online Certificate Revocation Protocol Scherling, Mark
- RE: Online Certificate Revocation Protocol Bob Jueneman
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- RE: Online Certificate Revocation Protocol Scherling, Mark
- RE: Online Certificate Revocation Protocol Santosh Chokhani
- RE: Online Certificate Revocation Protocol Scherling, Mark
- RE: Online Certificate Revocation Protocol Santosh Chokhani
- RE: Online Certificate Revocation Protocol Santosh Chokhani
- RE: Online Certificate Revocation Protocol Carlin Covey
- Re: Online Certificate Revocation Protocol Peter Gutmann
- RE: Online Certificate Revocation Protocol Lynn.Wheeler
- Re: Online Certificate Revocation Protocol Massimiliano Pala
- Re: Online Certificate Revocation Protocol jim
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