Re: [TLS] Additional TLS 1.3 results from Chrome

Eric Rescorla <> Mon, 18 December 2017 21:04 UTC

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From: Eric Rescorla <>
Date: Mon, 18 Dec 2017 13:03:52 -0800
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To: David Benjamin <>
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Subject: Re: [TLS] Additional TLS 1.3 results from Chrome
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On Mon, Dec 18, 2017 at 11:35 AM, David Benjamin <>

> The web interface on some Canon printers breaks with 1.3-capable
> ClientHello messages. We have purchased one and confirmed this with a
> PIXMA MX492. User reports suggest that it also affects PIXMA MG3650
> and MX495 models. It potentially affects a wide range of Canon
> printers.
> These printers use the RSA BSAFE library to implement TLS and this
> library implements the extended_random extension and assigns it number
> 40. This collides with the key_share extension and causes 1.3-capable
> handshakes to fail.
> We understand that this has been fixed in BSAFE ≥ 4.1, but older
> versions still exist in the world. Canon is aware of this and is
> planning on issuing firmware updates, although the uptake of firmware
> for printers is typically poor.
> However, since extension numbers are essentially infinite, this WG may
> consider renumbering key_share to avoid the issue.

I think this would be fine, but not imperative.


> Dymo (the label-printer manufacturer) is experiencing a similar[2]
> issue with some of their software. We have not been able to reproduce
> but one guess is that they are also using BSAFE.
> (Lastly, we note that in the paper "On the Practical Exploitability of
> Dual EC in TLS Implementations", the authors remarked that they had no
> evidence that a version of BSAFE with extended_random support ever
> shipped. TLS 1.3 appears to have tripped over it.)
> Cisco Firepower
> After receiving a report of issues with a Cisco “Firepower” device we
> purchased one to try and reproduce the issue.
> We found that Firepower middleboxes in "Decrypt - Resign" mode
> terminate TLS connections, but do not send a compliant ClientHello:
> They modify the original ClientHello to remove unknown ciphersuites,
> EMS, and NPN, but incorrectly forward most other fields from the
> original ClientHello, including unknown extensions (supported_versions
> and key_shares), and the client random. This breaks TLS 1.3 servers.
> Additionally, these devices forward the server random rather than
> generating their own (which will break when deploying the TLS 1.3
> anti-downgrade feature), and forward unknown signature algorithms
> (which will break when deploying, e.g., Ed25519).
> Disabling "Decrypt - Resign" mode appears to work around this issue.
> To fix this mode, these devices will need to stop forwarding unknown
> extensions and generate their own random values.
> We have provided Cisco with this information.
> Avast Antivirus
> We have received one report that Avast’s HTTPS scanning feature breaks
> connections that negotiate TLS 1.3. The user reported that disabling
> HTTPS scanning solved the issue. We were not able to reproduce so this
> might only occur with older versions of Avast.
> [1]
> [2]
> interference-in-chrome-63-using-the-js-sdk/
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