OCSP stapling

OCSP (Online Certificate Status Protocol) 是用來檢查 SSL certificate 是否被撤銷的方法。OCSP server 接受 HTTP POST 後,回答 client 這個 SSL certificate 是否仍然有效。

對於 client 來說,這主要有兩個問題:

  • client 需要多花時間連到 OCSP server 確認。
  • 隱私問題:OCSP server 會知道「這個使用者試著連到使用這個 SSL certificate」的資訊。

而對於 OCSP server 來說,這個方法的 scalability 很差,熱門的站台會產生大量的流量打進 OCSP server。

OCSP stapling 則是解決這個問題的方法。藉由 server 向 OCSP server 要一次 OCSP response 後,直接傳回 OCSP response 給 client (通常是 browser) 避開了上面的問題。這個方法也逐漸在普及了:(取自英文版維基百科文章內的說明)

OCSP stapling has not seen broad deployment to date, however this is changing. The OpenSSL project included support in their 0.9.8g release with the assistance of a grant from the Mozilla Foundation.

Apache HTTP Server supports OCSP stapling since version 2.3.3, the nginx web server since version 1.3.7, and LiteSpeed Web Server since version 4.2.4. and Microsoft's IIS since Windows Server 2008

On the browser side, OCSP stapling was implemented in Firefox 26 and in Internet Explorer since Windows Vista.

所以已經有不少 client 與 server 都支援了...

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