I am looking at a wireshark capture of the cipher suites sent by my browser to the server during an SSL handshake; however, almost 90% of them use CBC, with 2 or 3 having GCM.

Why is CBC most used? Is there a specific property that makes CBC preferred by web communications?

Also literature suggests that the non-feedback modes (e.g., counter mode) perform better in practice; however GCM shows up in only a few cipher suites. Any ideas why?


Historically, CBC was for long the dominant block cipher mode, but in recent years there's been a slow but firm move away from it, based on two trends:

  1. The move toward authenticated encryption as the "go-to" ciphers for practical applications;
  2. A reevaluation of the merits of CTR-based modes over CBC, driven by a variety of factors like:
    • The proliferation of attacks against CBC-based ciphersuites;
    • The simplicity and performance of CTR.

So you see a lot of CBC because it was the king for a long time, and it's only going away slowly. This blog entry by Cloudfare has graphs of the SSL cipher suites they're seeing and shows AES-GCM gradually gaining over AES-CBC.

Two references I've found useful:

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    $\begingroup$ Backwards compatibility just rules the world ... $\endgroup$ – SEJPM Sep 30 '16 at 19:08
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    $\begingroup$ Note that CCM, EAX and of course GCM use CTR mode underneath. $\endgroup$ – Maarten Bodewes Sep 30 '16 at 21:51
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    $\begingroup$ @MaartenBodewes: to be clear, that's what I meant when I said "CTR-based" instead of just "CTR." $\endgroup$ – Luis Casillas Sep 30 '16 at 22:12
  • $\begingroup$ @LuisCasillas Well, that's nice once you know that many authenticated ciphers are based on CTR, but otherwise that's a pretty impossible connection to make. I just mentioned it because I thought that statement needed an example or two. And, in that sense, the note wasn't directed to you. $\endgroup$ – Maarten Bodewes Sep 30 '16 at 22:24

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