I found an interesting post on another website by a Mr. Chris R. Chapman. The author explains what I had guessed about this situation.
Today, a friend remarked to me that according to an SSL framecheck site he uses (Fortify SSL Check) his 64–bit Win7 + IE8 configuration was registering as 128 bit AES by default, and not – as he anticipated – 256 bit AES (as FireFox does, for example).
This is true and by design: The IE team made a conscious decision to trade off cipher strength for speed, since 128 bits is sufficient for securing most channels reliably and not impact speed on HTML-heavy sites. However, what if you do want 256–bit AES cipher strength as the default for securing IE’s channel? Fear not – here’s the resolution I was able to surface:
- Launch “Edit Group Policy” from the Start menu.
- Navigate to Computer Configuration—>Administrative Templates—>SSL Configuration Settings via the treeview control.
- Note that in the right pane, the entry is not enabled – double-click the entry to bring up the edit dialog and select the “Enable” radio button.
- In the text box under Options on the left side, paste-in the comma-delimited list from the following file: File Attachment: ie8_ciphersuites_group_policy.txt (1 KB)
- Click OK and close off the policy editor dialog.
- Reboot.
- Navigate to the Fortify site and verify that AES 256 is your default cipher strength.
The “magic” that makes this happen is in the list of ciphers which are parsed sequentially – I simply changed the order of the first four entries from:
TLS_RSA_WITH_AES_128_CBC_SHA256,TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_256_CBC_SHA256,TLS_RSA_WITH_AES_256_CBC_SHA
to:
TLS_RSA_WITH_AES_256_CBC_SHA256,TLS_RSA_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_128_CBC_SHA256,TLS_RSA_WITH_AES_128_CBC_SHA
Enjoy responsibly.
So IE8 does indeed default to a 128 cipher the vast majority of the time regardless of the 256 cipher listing in HELP/ABOUT, unlike other browsers such as Firefox. Curious as to people's thoughts on this?