RE: Online Certificate Revocation Protocol

[Santosh Chokhani <[e-mail]>]

Mark:
 
One more thing, revoking the public encryption key is also not a good idea
in all cases.  When key recovery (specifically key escrow) is employed that
provides the first party to recover their private decryption keys, there is
no need to revoke the certificate.
 
-----Original Message-----
From: Santosh Chokhani 
Sent: Tuesday, June 12, 2001 4:38 PM
To: 'Scherling, Mark'; Santosh Chokhani; [e-mail]
Cc: Ietf-Pkix
Subject: RE: Online Certificate Revocation Protocol



Please see responses in-line.

-----Original Message-----
From: Scherling, Mark [mailto:[e-mail]]
Sent: Tuesday, June 12, 2001 4:30 PM
To: 'Santosh Chokhani'; Scherling, Mark; [e-mail]
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:[e-mail]]
Sent: Tuesday, June 12, 2001 12:56 PM
To: Scherling, Mark; Santosh Chokhani; [e-mail]
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
service
 
I 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:[e-mail]]
Sent: Tuesday, June 12, 2001 3:31 PM
To: 'Santosh Chokhani'; [e-mail]; 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:[e-mail]]
Sent: Tuesday, June 12, 2001 11:57 AM
To: [e-mail]; Scherling Mark
Cc: Ietf-Pkix
Subject: RE: Online Certificate Revocation Protocol



I agree with "thayes". 



-----Original Message----- 
From: [e-mail] [ mailto:[e-mail]
<mailto:[e-mail]> ] 
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:[e-mail] <mailto:[e-mail]> ] 
>Sent: Tuesday, June 12, 2001 9:07 AM 
>To: Paul Gogarty; [e-mail]; [e-mail] 
>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: [e-mail] 
>[ mailto:[e-mail] <mailto:[e-mail]>
]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 
> 
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> 
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>