AES-CBC is going the way of the dodo

by Vlad Krasnov.

A little over a year ago, Nick Sullivan talked about the beginning of the end for AES-CBC cipher suites, following a plethora of attacks on this cipher mode.

Today we can safely confirm that this prediction is coming true, as for the first time ever the share of AES-CBC cipher suites on Cloudflare’s edge network dropped below that of ChaCha20-Poly1305 suites, and is fast approaching the 10% mark.


CC BY-SA 2.0 image by aesop

Over the course of the last six months, AES-CBC shed more than 33% of its “market” share, dropping from 20% to just 13.4%.

Ciphers

All of that share, went to AES-GCM, that currently encrypts over 71.2% of all connections. ChaCha20-Poly1305 is stable, with 15.3% of all connections opting for that cipher. Surprisingly 3DES is still around, with 0.1% of the connections.

The internal AES-CBC cipher suite breakdown as follows:

CBC

The majority of AES-CBC connections use ECDHE-RSA or RSA key exchange, and not ECDHE-ECDSA, which implies that we mostly deal with older clients.

RSA is also dying

In other good new, the use of ECDSA surpassed that of RSA at the beginning of the year. Currently more than 60% of all connections use the ECDSA signature.

Although 2048-bit RSA is not broken, it is generally considered less secure than 256-bit ECDSA, and is significantly slower to boot.

signatures

PFS is king

Last, but not least, 98.4% of all connections are PFS, using ECDHE for key exchange. That's up from 97.6% six months ago.

All in all we see the continuation of the positive trend on the web towards safer and faster cryptography. We believe this trend will continue with the finalization of TLS 1.3 later this year.

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