[Mono-dev] Proposal: Change SignCode default from MD5 to SHA1

[Eric Lawrence]

As far as I know, all systems that support MD5 Authenticode signatures also
support SHA1 signatures, so breakage from this change seems quite unlikely.

(Alas, this is not true of SHA256, which is only supported on modern
versions of Windows, and not presently supported by signcode.exe at all).

On Tue, Dec 15, 2015 at 1:12 PM, Alexander Köplinger <
alexander.koeplinger at xamarin.com> wrote:

> I like it. Does changing the default have any backwards compatibility
> issues?
>
> Looks like the default comes from
> https://github.com/mono/mono/blob/b7a308f660de8174b64697a422abfc7315d07b8c/mcs/class/Mono.Security/Mono.Security.Authenticode/AuthenticodeFormatter.cs#L80 so
> we’d need to decide if we should change it there or make a targeted fix
> just for signcode.
>
> - Alex
>
> Am 15.12.2015 um 20:00 schrieb Eric Lawrence <bayden at gmail.com>:
>
> (resend, as Miguel suggested I should join the list)
>
> Today, the signcode application distributed with Mono defaults to using
> MD5 for Authenticode signing. This has resulted in vulnerable signatures on
> at least two broadly distributed projects (CoPilot and WordPress Desktop;
> see http://textslashplain.com/2015/12/15/hashes-and-code-signing/).
>
> MD5 signatures are dangerous because the collision attacks against MD5 get
> better and cheaper with each passing day, and any MD5 signature is
> vulnerable to abuse for the lifetime of the signing certificate—the package
> WordPress signed last week could be exploited until 11/21/2018 unless
> Automattic is willing to revoke their signing certificate before that time
> (costly).
>
> SHA1 is considerably stronger than MD5 and signcode already supports it;
> it just needs to be made default. The command line argument (-a md5) could
> be used for anyone that really needs an MD5 signature for any reason.
>
> Thanks for your consideration!
>
> -Eric Lawrence
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>
>
>


-- 
Eric Lawrence
Bayden Systems
http://www.bayden.com
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