Thunderbird S/MIME not compliant with RFC 5751



3 years ago
7 months ago


(Reporter: Anton, Unassigned)


40 Branch

Firefox Tracking Flags

(Not tracked)




3 years ago
User Agent: Mozilla/5.0 (X11; Linux i686; rv:31.0) Gecko/20100101 Firefox/31.0

Steps to reproduce:

At first: Many thanks for keeping Thunderbird alive.
The latest version does not fully comply with RFC 5751 regarding the S/MIME settings.
I sent S/MIME encrypted emails from Outlook 2010 v14.0.7149  to Thunderbird 31.7, 38, 40 and Seamonkey 2.33, 2.38, requesting in the attribute "SMIMECapabilities" the encryption with AES 256 and the hash SHA512.
I replied to these emails with TB and SM, and checked the applied encryption and hashes in Outlook. There it is possible to set the demanded and display the applied encryption and hashes.
Machines used for check: Mac OS X with TB 31, Linux i386 with all clients.

Actual results:

TB 31 applied always 3DES for content encryption and SHA1 for hashing. TB 38, 40 and SM 2.33, 2.38 used 3DES and SHA256.

Expected results:

Following RFC 5751 the responding clients should use the settings demanded by the sender. In case of an erroneous or missing S/MIME attribute from Outlook ("unknown capabilities") AES 128 should have been applied.

All results and the relevant RFC sections are stored here:
SHA-1 is being retired and removed because it's two weak.
Blocks: 1018259
Ever confirmed: true

Comment 2

2 years ago
I also thank all the programmers for working on Thunderbird.

Regarding this bug I'd like to know whether someone will work on this? It is confirmed that SHA-1 is weak and it looks as if Thunderbird is now using SHA-256 (solved in 1018259).

But what about 3DES? This is also not state of the art. Microsoft Outlook is using AES-256 for encryption. Wouldn't it be fine to also have AES-256 as default?

Comment 3

2 years ago
Currently there are no active developers who are focused on actively improving S/MIME functionality in Thunderbird. If there is an issue of serious concern, then we would try to motivate someone who works more broadly to try to address it. But "does not fully comply" is not a high enough bar.

Contributors and patches are welcome.

Comment 4

7 months ago
This is still the case in Thunderbird 45.

I tried sending an email to myself and found out, that the selected encryption for my email was still 3DES (which is broken).

On you can paste the encrypted email text part (from the source Ctrl+U below "Content-Description: S/MIME Encrypted Message") and see the decrypted details (  for example )

There you find the string

    OBJECT IDENTIFIER1.2.840.113549.3.7des-EDE3-CBC

which shows that 3DES is used.

A secure encryption like AES, camelia, aria or chacha20 shouldh have been selected to encrypt my mail body.


7 months ago
Duplicate of this bug: 1364568
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