The validity period of your root CA and server certificates depends on your
Certificate Policy (CP).
CP is a document that governs the operation of your PKI. It can be very
simple and it can also be very complex.
There are a lot of CPs which you can use as a reference.
For server cert, with 1024 bit RSA with 2 to 3 years might be sufficient.
Of course you have to renew your server cert when the cert is about to
expired (1/2 of the validity period).
You can renew the server cert, which mean you do not need to change the
server private key or rekey.
In rekey, the server got a new keypair and a new cert. The option you choose
should be described in the CP.
When the server cert is changed, you do not need to update (or touch) the
client.
The reason is, during the SSL handshake, the server always sends its
certificate to the client (unless you are using SSL with pre-shared-key).
Hence, server cert renew or reky is transparent to client.
Erwin
--------------------------------------------------
From: "Dinh, Thao V CIV NSWCDD, K72" <thao.d...@navy.mil>
Sent: Thursday, April 12, 2012 7:56 AM
To: <openssl-users@openssl.org>
Subject: RE: expired ssl certificate
Thank You very, very much for all for help. I have a couple more
questions:
1) what is max time you can have on expiration ??
2) You wrote
Create a long lived self-signed CA certificate (for example: 20 or 30
years)..
Have this self-signed CA (trust anchor) created in step-1 issues the
server certificate. For this server certificate, validity period does
not matter.
Should we make this server certificate as long as CA ?? Because making it
short ( 5 years) , the handshanking will fail due to expired cert??
Thank again Nou, Erwin...
Thao Dinh
-----Original Message-----
From: owner-openssl-us...@openssl.org
[mailto:owner-openssl-us...@openssl.org] On Behalf Of Erwin Himawan
Sent: Wednesday, April 11, 2012 2:57 PM
To: openssl-users@openssl.org
Subject: Re: expired ssl certificate
Reading Nou's proposal, I have the impression that the client needs to be
modified to accept expired server's certificate. Is my understanding
correct? If my understanding is corrrect, the client needs to be updated.
If the client needs to be updated, In my opinion, it is simpler to update
the client with a new server certificate.
However, you should not use a selfsigned certificate for your serve
certificate. Instead, I am proposing to create a chain of certificate
(PKI). You could avoid this problem in the future by creating a simple
PKI. FUrther you could expand this PKI to issue certificate for other
application.
This is what I am proposing:
1. Create a long lived self-signed CA certificate (for example: 20 or 30
years); This self-signed certificate is called trust anchor certificate.
Make sure, basic constraint CA is set to true.
Do not make the expiration less than 5 years, since you will have the
same issue again in the next 5 year to roll-over your trust anchor
certificate. Also, keep the private key of this CA as safe as possible.
THis is your root of trust. If you compromise this root CA private key,
your PKI becomes void.
2. Distribute this self-signed certificate to all clients and install this
as the trusted certificate.
3. Have this self-signed CA (trust anchor) created in step-1 issues the
server certificate. For this server certificate, validity period does not
matter. Of course you do not want to make the validity period too short
since you have to frequently update the server certificate when it is
expired.
Using this proposed method, you can update or change the server
certificate as often as you like.
The server certificate is typically included in the SSL's ServerHello
message, so the client always got the server certificate during SSL
handshake. I think (?) the server could also include the chain of
certificate up to the trust anchor certificate.
When the client receives the server certificate issued by the self-signed
CA (the self-signed CA certificate could also be included in the
ServerHello), the client can verify this certificate chain up to the
self-signed CA certificate. If the chain can be verified, then the server
certificate is successfully validated. Hence, the server can be
cryptographically authenticated.
Using Nou's proposal, your client would practically accept any self-signed
certificate and prone to man-in-the-middle attack. The client can
cryptographically verify the server certificate, but the client can not
cryptographically authenticate the server since the client does not have
the knowledge of the server's legitimate public key. Using my proposal,
your client can cryptographically authenticate the server, by verifying
the digital signature in the server's certificate using the (selfsigned)
CA certificate. The selfsigned CA certificate is then verified against a
list of trusted certificates. My proposal is actually similar with what
you are doing currently. The difference between my proposal and yours is:
in yours, you verify the server certificate against a list of trusted
certificates. In my proposal, you verify the server certificate using the
CA certificate which is in a list of trusted certificates.
Erwin
On Wed, Apr 11, 2012 at 11:34 AM, Nou Dadoun <ndad...@teradici.com> wrote:
I'm no ssl guru either but I'll make some brief comments and let others
jump in if I'm too far off the mark.
1. If you use the standard verify and the peer presents an expired
certificate, the certificate will not be verified and the connection will
fail.
2. The verification callback is called after the "regular" verification
is performed, here's a simple example I posted with my own question
yesterday:
static int verify_callback(int ok, X509_STORE_CTX *stor)
{
if(!ok)
{
printf("verify_callback Certificate Verification Error: %s\n",
X509_verify_cert_error_string(stor->error));
}
else
{
printf("verify_callback Certificate Verification Success\n");
}
return ok;
}
The ok parameter tells you whether the certificate passed so that if it's
not ok (didn't pass) you can examine the reason/error and the certificate
itself to see whether or not you want to over-rule that result. The return
value indicates whether you want to accept it or not - the above example
only reports the result (without changing it) and (if it fails) the reason
for failure without changing anything. If it's not ok and you look at the
cert and it's expired but you don't care, return 1 and it will be
accepted. Look at the examples in the pdf for some examples.
As I said earlier, standard warnings apply - you're overruling standard
security mechanisms for your own purposes which can be dangerous if you're
not careful.
3. I think I've answered that above .... N
---
Nou Dadoun
ndad...@teradici.com
604-628-1215
-----Original Message-----
From: owner-openssl-us...@openssl.org
[mailto:owner-openssl-us...@openssl.org] On Behalf Of Dinh, Thao V CIV
NSWCDD, K72
Sent: April 11, 2012 4:19 AM
To: openssl-users@openssl.org
Subject: RE: expired ssl certificate
Hi Nou
Please help me understand more about this subject ( I am new to Openssl)
1. What happen if the peer presents an expired certificate and we do not
implement callback using SSL_CTX_set_verify with SSL_VERIFY_PEER flag set,
will the SSL_connect or SSL_accept fail ???
2. What is the function of verification callback ? Just "report" error of
expired certificate or actually let expired certificate be accepted ??
what is X509_.. function shoud I uses to let expired cert being accept ??
3. what is the different between standard verify operation and the verify
callback ???
Thank You
Thao Dinh
-----Original Message-----
From: owner-openssl-us...@openssl.org
[mailto:owner-openssl-us...@openssl.org] On Behalf Of Nou Dadoun
Sent: Tuesday, April 10, 2012 3:15 PM
To: openssl-users@openssl.org
Subject: RE: expired ssl certificate
You can use a verification callback to look at the certificate after the
standard verify operation has been performed to decide whether or not to
allow the certificate anyway.
Look at the O'Reilly book
(http://doc.hackbbs.org/Reseaux/O_Reilly_-_Network_Security_with_OpenSSL.pdf
) page 132 or so has some sample code you can probably modify.
Standard warnings apply .. N
---
Nou Dadoun
ndad...@teradici.com
604-628-1215
________________________________
From: owner-openssl-us...@openssl.org
[mailto:owner-openssl-us...@openssl.org] On Behalf Of Srihari, Gautam
Sent: April 10, 2012 3:04 AM
To: openssl-...@openssl.org; openssl-users@openssl.org
Subject: expired ssl certificate
Hi,
I have a server application and the client uses https to connect
to the server. For this I had created an openssl self signed certificate
cacert.pem which has been distributed to all the client applications.
Now unfortunately the certificate has expired. I can create a new
certificate.
But distributing to all the clients is going to be difficult.
Is there some way by using open ssl, I can make the server ignore
expired certificates
so I don't have to ask each client to update to a new certificate?
The crux of the problem is that I want to continue to allow clients to use
the server without
Having them to upgrade anything i.e change should be done only on the
server side.
Reg.,
Gautam
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