Re: How to disable tls 1 and tls 1.1

helo
thank you all for your involvement, thanks to you the problem has been 
solved
regards


----- Original Message ----- 
From: "Viktor Dukhovni via Exim-users" <[email protected]>
To: <[email protected]>
Sent: Tuesday, May 27, 2025 3:43 AM
Subject: [exim] Re: How to disable tls 1 and tls 1.1


> On Mon, May 26, 2025 at 08:47:35PM +0000, Slavko via Exim-users wrote:
>
>> >(HMAC) in TLS in the context of SMTP.  There are some browser-specific
>> >issues with CBC ciphers because TLS did MAC-then-encrypt rather than
>> >encrypt-then-MAC, but these required scripting many connectiosn to
>> >possibly leak cookie information.  These attacks don't apply to SMTP.
>>
>> AFAIK 3DES was deprecated (and disallowed after 2023) by NIST.
>> I believe, that there is some good reason for that...
>
> The 3DES block size of 64 bits is no longer favoured, performance is not
> great, and 112-bit security is frowned upon by nation states that
> typically ask for 192-bit security for the more senstive use-cases.
> But, there I've seen no practical attacks on 3DES-CBC beyond the generic
> CBC mac-then-encrypt issues in browsers.
>
>> >This is a reasonable choice for the *generic* application, which is
>> >not doing opportunistic TLS, and possibly shares some of the browser
>> >attack surfaces.  It is less compelling for SMTP, but with the passage
>> >of time, as noted above, the impact of dropping support for TLS 1.0/1.1
>> >is becoming insignificant...
>>
>> I still do not understand one thing: why is as much effort invested
>> to advocate old (deprecated) versions of TLS.
>
> The effort is not to "advocate" these, but rather to encourage you to
> not go out of your way to spend effort to disable them, in a protocol
> where otherwise transmission is acceptable in cleartext.
>
> With sufficiently recent OpenSSL, at the default security level you
> get TLS >= 1.2 out of the box.  At SECLEVEL=0 you get best effort
> security, which is better than no security if you still have clients
> that don't support TLS >= 1.2.  Increasingly that's no longer a concern,
> so your call.
>
>> I understand, that deprecated doesn't mean disallowed, i understand it
>> as "awoid if possible".
>
> Which happens automatically when both ends support TLS 1.2 or better.
> Again, there's little harm now to explicitly disable the older
> protocols, but also little compelling reason to do it.
>
> Do what makes sense to you, and don't worry about it either way, this
> is far from your most pressing security concern.
>
> -- 
>    Viktor.
>
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