Re: [Cbor] MIME tag 257 vs 36

Jim Schaad <> Tue, 15 September 2020 21:21 UTC

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From: Jim Schaad <>
To: 'Laurence Lundblade' <>,
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Date: Tue, 15 Sep 2020 14:21:23 -0700
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Subject: Re: [Cbor] MIME tag 257 vs 36
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-----Original Message-----
From: CBOR <> On Behalf Of Laurence Lundblade
Sent: Tuesday, September 15, 2020 1:17 PM
Subject: [Cbor] MIME tag 257 vs 36

Does this seem right?

MIME tag 257 can carry MIME messages that have any content transfer encoding. It is not necessary to use tag 36 for content transfer encoding 7bit, base64 and quoted printable. You cannot however use tag 36 with content transfer encoding binary. You probably can use tag 36 with content transfer encoding 8bit.

[JLS] I would disagree.  You cannot use tag 36 for 8bit encoding unless the charset of the message is either US-ASCII or UTF8.  If this is encoding using the code page 932 (Shift JIS) then while it is 8bit it is not UNICODE and thus requires tag 257.

It is thus recommend protocols use tag 257 when encoding MIME messages. Use of tag 36 should be avoided. It’s primary use is in protocols that were defined before tag 257 was defined.

I don’t think this is an issue, but I have little bit of worry that tag 36 might give you some end-of-line canonicalization because it is UTF-8 that tag 257 won’t.

[JLS]  I can't see that EOL canonicalization would be an issue here.


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