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Found at: raymii.org:70/OCSP_Stapling_on_nginx.txt

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---
Title       : 	OCSP Stapling on nginx
Author      : 	Remy van Elst
Date        : 	03-02-2014
URL         : 	https://raymii.org/s/tutorials/OCSP_Stapling_on_nginx.html
Format      : 	Markdown/HTML
---
When connecting to a server, clients should verify the validity of the server
certificate using either a Certificate Revocation List (CRL), or an Online
Certificate Status Protocol (OCSP) record. The problem with CRL is that the
lists have grown huge and takes forever to download.
OCSP is much more lightweight, as only one record is retrieved at a time. But
the side effect is that OCSP requests must be made to a 3rd party OCSP responder
when connecting to a server, which adds latency and potential failures. In fact,
the OCSP responders operated by CAs are often so unreliable that browser will
fail silently if no response is received in a timely manner. This reduces
security, by allowing an attacker to DoS an OCSP responder to disable the
validation.

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The solution is to allow the server to send its cached OCSP record during the
TLS handshake, therefore bypassing the OCSP responder. This mechanism saves a
roundtrip between the client and the OCSP responder, and is called OCSP
Stapling.
The server will send a cached OCSP response only if the client requests it, by
announcing support for the status_request TLS extension in its CLIENT HELLO.
Most servers will cache OCSP response for up to 48 hours. At regular intervals,
the server will connect to the OCSP responder of the CA to retrieve a fresh OCSP
record. The location of the OCSP responder is taken from the Authority
Information Access field of the signed certificate.
[This tutorial is also available for Apache][2]
### What is OCSP Stapling
OCSP stapling is defined in the [IETF RFC 6066][3]. The term "stapling" is a
popular term used to describe how the OCSP response is obtained by the web
server. The web server caches the response from the CA that issued the
certificate. When an SSL/TLS handshake is initiated, the response is returned by
the web server to the client by attaching the cached OCSP response to the
CertificateStatus message. To make use of OCSP stapling, a client must include
the "status_request" extension with its SSL/TSL Client "Hello" message.
OCSP stapling presents several advantages including the following:
  * The relying party receives the status of the web servers certificate when it is needed (during the SSL/TLS handshake).
  * No additional HTTP connection needs to be set up with the issuing CA.
  * OCSP stapling provides added security by reducing the number of attack vectors.
[Read][4] [one][5] [of][6] [the][7] [following][8] [links][9] for [more][10]
information on OCSP and OCSP stapling.
### Requirements
You need at least nginx 1.3.7 for this to work. This is not available in the
current Ubuntu LTS releases (12.04), [it has 1.1.19][11] and on CentOS you need
EPEL or the official repositories. However, it is easy [to install the latest
version of nginx.][12]
You also need create a firewall exception to allow your server to make outbound
connections to the upstream OCSP's. You can view all OCSP URI's from a website
using this one liner:
    
    
    OLDIFS=$IFS; IFS=':' certificates=$(openssl s_client -connect google.com:443 -showcerts -tlsextdebug -tls1 2>&1 
    
It results for google.com in:
    
    
    http://clients1.google.com/ocsp
    http://gtglobal-ocsp.geotrust.com
    
### nginx Configuration
Add the below configuration to your https (443) `server` block:
    
    
    ssl_stapling on;
    ssl_stapling_verify on;
    resolver 8.8.8.8 8.8.4.4 valid=300s;
    resolver_timeout 5s;
    
For the OCSP stapling to work, the certificate of the server certificate issuer
should be known. If the `ssl_certificate` file does not contain intermediate
certificates, the certificate of the server certificate issuer should be present
in the `ssl_trusted_certificate` file.
My certificate for raymii.org is issues by `Positive CA 2`. That certificate is
issued by `Addtrust External CA Root`. In my nginx `ssl_certificate` file all
these certificates are present. If that for you is not the case, create a file
with the certificate chain and use it like so:
    
    
      ssl_trusted_certificate /etc/ssl/certs/domain.chain.stapling.pem;
    
Before version 1.1.7, only a single name server could be configured. Specifying
name servers using IPv6 addresses is supported starting from versions 1.3.1 and
1.2.2. By default, nginx will look up both IPv4 and IPv6 addresses while
resolving. If looking up of IPv6 addresses is not desired, the `ipv6=off`
parameter can be specified. Resolving of names into IPv6 addresses is supported
starting from version 1.5.8.
By default, nginx caches answers using the TTL value of a response. The
(optional) `valid` parameter allows overrides it to be 5 minutes. Before version
1.1.9, tuning of caching time was not possible, and nginx always cached answers
for the duration of 5 minutes.
Restart your nginx to load the new configuration:
    
    
    service nginx restart
    
And it should work. Let's test it.
### Testing it
Fire up a terminal and use the following OpenSSL command to connect to your
website:
    
    
    openssl s_client -connect example.org:443 -tls1 -tlsextdebug -status
    
In the response, look for the following:
    
    
    OCSP response:
    ======================================
    OCSP Response Data:
        OCSP Response Status: successful (0x0)
        Response Type: Basic OCSP Response
        Version: 1 (0x0)
        Responder Id: 99E4405F6B145E3E05D9DDD36354FC62B8F700AC
        Produced At: Feb  3 04:25:39 2014 GMT
        Responses:
        Certificate ID:
          Hash Algorithm: sha1
          Issuer Name Hash: 0226EE2F5FA2810834DACC3380E680ACE827F604
          Issuer Key Hash: 99E4405F6B145E3E05D9DDD36354FC62B8F700AC
          Serial Number: C1A3D8D00D72FCE483CD84759E9EC0BC
        Cert Status: good
        This Update: Feb  3 04:25:39 2014 GMT
        Next Update: Feb  7 04:25:39 2014 GMT
    
That means it is working. If you get a response like below, it is not working:
    
    
    OCSP response: no response sent
    
You can also use the [SSL Labs][13] test to see if OCSP stapling works.
### Sources
  * [nginx documentation for resolver][14]
  * [nginx documentation for ssl_stapling][15]
   [1]: https://www.digitalocean.com/?refcode=7435ae6b8212
   [2]: https://raymii.org/s/tutorials/OCSP_Stapling_on_Apache2.html
   [3]: http://tools.ietf.org/html/rfc6066
   [4]: http://en.wikipedia.org/wiki/OCSP_stapling
   [5]: http://en.wikipedia.org/wiki/Online_Certificate_Status_Protocol
   [6]: http://security.stackexchange.com/questions/29686/how-does-ocsp-stapling-work
   [7]: https://blog.mozilla.org/security/2013/07/29/ocsp-stapling-in-firefox/
   [8]: http://www.thawte.com/assets/documents/whitepaper/ocsp-stapling.pdf
   [9]: http://news.netcraft.com/archives/2013/04/16/certificate-revocation-and-the-performance-of-ocsp.html
   [10]: https://wiki.mozilla.org/Security/Server_Side_TLS
   [11]: http://packages.ubuntu.com/precise/nginx
   [12]: http://wiki.nginx.org/Install
   [13]: https://ssllabs.com
   [14]: http://nginx.org/en/docs/http/ngx_http_core_module.html#resolver
   [15]: http://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_stapling
---
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