Re: [Acme] WG last call for draft-ietf-acme-email-smime-06

"Salz, Rich" <> Tue, 05 May 2020 15:25 UTC

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From: "Salz, Rich" <>
To: Alexey Melnikov <>, Ryan Sleevi <>, Ben Schwartz <>
CC: "" <>
Thread-Topic: [Acme] WG last call for draft-ietf-acme-email-smime-06
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Date: Tue, 5 May 2020 15:24:59 +0000
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Subject: Re: [Acme] WG last call for draft-ietf-acme-email-smime-06
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Thanks for the discussion.  I will point out that this has already moved past WGLC (I am late on the writeup and IESG submission), but in view of the pandemic messing with everyone’s schedules, and since this has not had a lot of WG commentary so far, I’d like to encourage this.  We’ll do a shorter WGLC re-review if there’s another draft.  And if we need any consensus calls (“anyone cannot live with X”) please reach out.

Hope everyone is staying safe and healthy.

From: Alexey Melnikov <>
Date: Tuesday, May 5, 2020 at 11:19 AM
To: Ryan Sleevi <>om>, Ben Schwartz <>
Cc: "" <>rg>, Rich Salz <>
Subject: Re: [Acme] WG last call for draft-ietf-acme-email-smime-06


Let me try to elaborate on the current choice and talk about alternatives. In general there are 3 ways how an ACME email challenge be conveyed in email:

1) In the subject line. Some structure would be helpful for automated software.

2) In a new header field.

3) In the body of the message, e.g. using "---BEGIN ACME CHALLENGE---" line in text/plain or the like.

Unfortunately all of these have their downsides:

#1 is unfriendly to users and can possibly trigger antispam processing. (Not sure how much of an issue the last part is)

#2 might not be accessible from libraries that don't support retrieval of arbitrary email header fields. (I am not sure how big of a deal this is, but I've heard some claims about that.) Also, non ACME aware clients might not be able to show this header field, making them unusable for manual processing.

#3 would either require use of text/plain (for simplicity of automated processing) or it would require HTML parser with downconversion to text/plain. I think the latter choice is a rather high barrier of entry for implementations that are not fully capable email clients, which I suspect would be too hight for some ACME servers.

So I am open to suggestions about the best choice. I think using some structured subject line (choice #1) or possibly text/plain choice #3 are the best. If there is a better structure for the subject header field, I would be happy to change the document.

Best Regards,