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 ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org
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