From nobody Mon Mar 5 15:20:08 2018 Return-Path: X-Original-To: openpgp@ietfa.amsl.com Delivered-To: openpgp@ietfa.amsl.com Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 2E368127AD4 for ; Mon, 5 Mar 2018 15:20:06 -0800 (PST) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -1.899 X-Spam-Level: X-Spam-Status: No, score=-1.899 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id pwkBoY_UksP3 for ; Mon, 5 Mar 2018 15:20:03 -0800 (PST) Received: from mail.mugenguild.com (mugenguild.com [5.135.189.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 94197120227 for ; Mon, 5 Mar 2018 15:20:02 -0800 (PST) Received: from localhost (62.43.79.238.dyn.user.ono.com [62.43.79.238]) by mail.mugenguild.com (Postfix) with ESMTPSA id 43EA05FAED for ; Tue, 6 Mar 2018 00:19:58 +0100 (CET) Date: Tue, 6 Mar 2018 00:19:51 +0100 From: Vincent Breitmoser To: openpgp@ietf.org Message-ID: <20180305231951.GA21944@calamity> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="tThc/1wpZn/ma/RB" Content-Disposition: inline Autocrypt: addr=look@my.amazin.horse; keydata=mQINBFAB3UABEADCyB/vbIBA3m1Bwc yjTieEMLySwYgt54EQ2hglOocdtIhqC+b05t6sLSkwx2ukxrU2cegnCBkdyF/FZ/+Et638CUEBbf 4bjplwpt2IPLazQgjkwjMuhz0OcYDpMhwimTvh3mIl+0wzpOts6mEmMw0QZdl3RXvIW+NSynOn7q mz/fAv4Htt6lv2Ka0s6R2voyi+5U7CcIqizPad5qZVn2uxmovcFreTzFt6nk37ZbbTfvA3e5F0bR RQeH3viT5XxpJF4Y76v/Ua+5N3Kd18K0sX85rD1G7cmxR2CZ5gW1X24sDqdYZdDbf10N39UIwjJH PTeuVMQqry792Ap0Etyj135YFCE0loDnZYKvy2Y1i0RuEdTUIonIHrLhe2J0bXQGbQImHIyMgB9/ lva8D+yvy2gyf2vjRhmJEEco7w9FdzP7p3PhKrUiTjRsjHw8iV8LOCFx9njZOq9mism9ZZ16tZpx 9mXOf11HcH1RtVuyyQRS/4ytQPzwshXdSDDW6Btkmo9AbZQKC54/hSyzpp3Br2T2xDH7ecnonDB/ jv8rWuKXSTbX3xWAIrNBNDcTYaNe4jkms4HF7jJE19eRlqsXMMx6Fxvrh4TtKICwJYJ3AUmXrK3X Ti/mjqYfJ1fpBn54rWs8nhSR1fuZPD+aMlcP8BDUPlNKPKtj0DGSh3/VlnnwARAQABtClWaW5jZW 50IEJyZWl0bW9zZXIgPGxvb2tAbXkuYW1hemluLmhvcnNlPokCOAQTAQIAIgUCVTNZmgIbAwYLCQ gHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQe9GDIN6t+hHcVg//aeiijNqsQ3pjbFQn3VvND7hNfJ vrVcLZ+U4kOzXPF818aVdOnDyNXyE17vBDDcvaZ730sCsZIRZJ3KhUJ+nPvdttKjUIGLARmx+pA3 Jl3IIv2uLtOb3I0TMuyfIGJVGF+q10/CeDMKVjKlmyOVrR0opkel+KEoN7VLq3Hf3zPKENO1HBgp LHeP31tlb9cgs+u4o2wLrVe9myHbuFBW7EjWbSvdz2zliwbsFeFVLMNcWrKAU0GkkiH69SgnwmXU RkhGma4L27GLtkHHufsxfbcPqPtmtCttsGZU4EmrghGUqVyDOxnn8ZqybzLrRfpin+OCIX+aHJz5 r2L8qtrP0LorNMX3Gopd26vfhNvq/wq8xk++bW1R5FmkaUhx9h+DhO2ybcg7p/E8JHc8zrWv+bb3 0o9lkrOaU8GxXrgtb1cjtbb+MxFvjm0Elw7MSZDG7sF/APFU6cwuIA9Nai/OGAUCSt/W2ecS8Zox cWWbGSEiDvjtEctkpmHjfVuGoL34966Olm41VdH+NjgoSYUJKx4Mty8DRcZxdyoXll84LvDkEEYK ZqOIACsJf8CDFvUkmhXc+moCj15Yxtj3/RslRVEiOUyrpDwB72zWcZG8YnzoyGxhcRIc/gFejO/y SI8bzCpYngeuTb5NjFG+ChGiInHbQcFeHBlaHtKi2o/B5axIO5Ag0EVDvOgQEQALJby/ztliToGE u1lslvWQUQ6teKZVUQ7hy9bM4N83G0AGLatUBHtY6PkJBe4XkIw3sK7LoFCV2W4GSt4zWp9l+kG3 /J8Ow7EFjN0F7DrCg0M0lMg9dQz9jYSoBR8skaH3BRzCq9AKIVKV94poL/G65289L7zKDHoZnnyF qbBtedYZir0SZx+kiouZ1qnmxRPaYmH2fkuiuvYEAyzLDLYM8F5gQhdZM4YVtuvSICYPet0z4CDi JX/vZmDi3AzzoEVaKeAM/0H9f9Ni547J2+8dZSllgTrA+fq0aMJVScAObIxTAQtEq0DoNBzPpVrm W10b4bmgePrAvNkifqSr5StymSBgwvoeW6GrJiyN4XhoLOadZzwgjqioR1nXw5tXtrr5sYdkZ06b 1WWHkxtu1hFTdLC7RYNxY07ytLNM+C2lplCwCwlWB7RwI9BL1Dhre4kv8uaaX2Gksaq9mDf9MSDW qQ0TJ/RAiwMGmFrzBEYI1J2Oyeshi/dqW4/OiZAukOIlxOnt6u8zU2KL6Qjxqqna0oTbS4Zv3fRd YkuUCL6CDEJdkuRAiW+Gw+lKcMjXqApEqixhaDkoB/kwtu+2gIFTzAxMfwFN1YtNc0kJZWnFkGIW MrrwTcOwAFzlFz7wn/EyMFtg+ERcqMX0+olXDwM8MODI2+BzulPuEDEteCw09hABEBAAGJAh8EGA ECAAkFAlQ7zoECGwwACgkQe9GDIN6t+hFjuQ//UQyg49f8TytUYQaBb8R0UfI+KhQFs1Nsz2z8a3 0CD1MeiHHYWdAcomVvTkg4g5LbnYHVDrj/XagY3FN/AIE97usFbsTG+rsWAOLi7N2dN2ehWZ634k MvrgyC9uTiOdkw31+B8K5MpyySgD8e6SAzRfiu06/bcQOUyJifw8Hudpj9by4uyGhSH+kHu4afrp OduUighbsGFtcuRwwQ/w/oSk68XvPUgiOQWMZh/pVoXdFyFvrt/hgArCi8dfy5UPK58nl7jPnu/I uQXrJ50nNAFIIxPVeo2/B83KAnEZPU+qWZsdba0V+FIIQQVizLtQFMuJJk4/UTAOfJ2tBpQ9PADX 6/scqDE7unXNWdxcHTjK7KmWjXC8CyhGOx8V/rb7Ial4mZo4cTED6SNlO7dV1XYwnSctL2HCYNM3 RUe4eJ7JWuu7/Nbf6yip2eq7BQKZ9hAH/se/OSZNYsEkZ4pxUc8W5U3uAZImUwC6L74SM0jBZIuD mQhOYX6sZZ6urIn/MYlj4/hqSBFS4vTK7nXRLmtr7+5T5U5srVseUiYc+l9pu9/XD8zGIu+M2xEd 41NwP44GDQTQm0bFljRv5fSblwmi56YHPFQUIh2RZNX3kOJgeyQ3enw5uY+7ocKRVP38hpnffliL lJcO6TtHWnElS3pACbTQM0RHJox3zqU3q6K3c= User-Agent: Mutt/1.9.1 (2017-09-22) Archived-At: Subject: [openpgp] Intended Recipient Fingerprint signature subpacket X-BeenThere: openpgp@ietf.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: "Ongoing discussion of OpenPGP issues." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 05 Mar 2018 23:20:06 -0000 --tThc/1wpZn/ma/RB Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Hey folks, dkg and I have been discussing an "Intended Recipient Fingerprint" subpacket, that pins a signature to be valid only in an encrypted context to the indicated recipient. Use of this subpacket removes some wiggling room for signed+encrypted messages. This can be used to prevent replay attacks, where a signature is taken out of its context and forwarded to a different recipient. Please see https://0xacab.org/schleuder/schleuder/issues/158 for a complete description of an attack scenario in the context of the Schleuder remailer. The given scenario is solved with this subpacket on the openpgp layer. Diff attached for rfc4880bis, please comment. - V --tThc/1wpZn/ma/RB Content-Type: text/x-diff; charset=us-ascii Content-Disposition: attachment; filename="intended-recipient.patch" diff --git a/middle.mkd b/middle.mkd index f09d85f..373aca2 100644 --- a/middle.mkd +++ b/middle.mkd @@ -1058,6 +1058,7 @@ The value of the subpacket type octet may be: 32 Embedded Signature 33 Issuer Fingerprint 34 Preferred AEAD Algorithms + 35 Intended Recipient Fingerprint 100 to 110 Private or experimental An implementation SHOULD ignore any subpacket of a type that it does @@ -1662,6 +1663,19 @@ signature, the key ID of the Issuer subpacket MUST match the low Note that the length N of the fingerprint for a version 4 key is 20 octets; for a version 5 key N is 32. +#### Intended Recipient Fingerprint + +(1 octet key version number, N octets of fingerprint) + +The OpenPGP Key fingerprint of the intended recipient primary key. If +one or more subpackets of this type are included in a signature, it +SHOULD be considered valid only in an encrypted context, where the key +it was encrypted to is one of the indicated primary keys, or one of +their subkeys. This can be used to prevent forwarding a signature +outside of its intended, encrypted context. + +Note that the length N of the fingerprint for a version 4 key is 20 +octets; for a version 5 key N is 32. ### {5.2.4} Computing Signatures --tThc/1wpZn/ma/RB-- From nobody Mon Mar 5 20:09:32 2018 Return-Path: X-Original-To: openpgp@ietfa.amsl.com Delivered-To: openpgp@ietfa.amsl.com Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 53781127444 for ; Mon, 5 Mar 2018 20:09:30 -0800 (PST) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -2.601 X-Spam-Level: X-Spam-Status: No, score=-2.601 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_PASS=-0.001] autolearn=ham autolearn_force=no Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=hush.ai Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id XC-hS3OUFxGk for ; Mon, 5 Mar 2018 20:09:28 -0800 (PST) Received: from smtp5.hushmail.com (smtp5.hushmail.com [65.39.178.142]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id DFBCA127869 for ; Mon, 5 Mar 2018 20:09:28 -0800 (PST) Received: from smtp5.hushmail.com (localhost [127.0.0.1]) by smtp5.hushmail.com (Postfix) with SMTP id 2EC2420DEA for ; Tue, 6 Mar 2018 04:09:28 +0000 (UTC) X-hush-tls-connected: 1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed; d=hush.ai; h=date:to:subject:from; s=hush; bh=GiV7YT4nJ0BSL7mF//SvWnGzKMdAonqqirWNGfQvMt0=; b=rAOyy4WcatAHbspNQIXGJnaqkihqNeYvPghoGD69isCWWm9I+RkSJJh2lFi7OSe/faaeDA0lLXWNU2IvTdYZZejKXWm6BgiUNwgmWqH6Imdn6MsiDtRi8JD+iWDOEoc/PiFkbhORWdojSBzkE5BaQ3EOWK2ZhA4++3sU2lq1AGPojHXdrfeBeJS0iVgryGnQAFHwxKigPpwljzKamo4pQAIf3EoBYq3+qGaqvuW5gR9BufPj8UvViFrTxOVNYOHYHxoQuJqMDs55u+t7h2lHY3uaxSZhzbwxWGi+MPtuzSjzstjSG4w7L1EJL3/xepfnaHQnmxcEbW99f6CiqBWkHQ== Received: from smtp.hushmail.com (w1.hushmail.com [65.39.178.83]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp5.hushmail.com (Postfix) with ESMTPS for ; Tue, 6 Mar 2018 04:09:27 +0000 (UTC) Received: by smtp.hushmail.com (Postfix, from userid 99) id C83C66010D; Tue, 6 Mar 2018 04:09:27 +0000 (UTC) MIME-Version: 1.0 Date: Mon, 05 Mar 2018 23:09:27 -0500 To: "openpgp" From: vedaal@nym.hush.com In-Reply-To: <20180305231951.GA21944@calamity> Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="UTF-8" Message-Id: <20180306040927.C83C66010D@smtp.hushmail.com> Archived-At: Subject: Re: [openpgp] Intended Recipient Fingerprint signature subpacket X-BeenThere: openpgp@ietf.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: "Ongoing discussion of OpenPGP issues." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 06 Mar 2018 04:09:30 -0000 On 3/5/2018 at 6:20 PM, "Vincent Breitmoser" wrote: > >Hey folks, > >dkg and I have been discussing an "Intended Recipient Fingerprint" >subpacket, that pins a signature to be valid only in an encrypted >context to the indicated recipient. > >Use of this subpacket removes some wiggling room for >signed+encrypted >messages. This can be used to prevent replay attacks, where a >signature >is taken out of its context and forwarded to a different recipient. ====== In principle, it's a good idea. But, the attacker could still send it along as a clearsigned message, and if the recipient accepts the message at face value, the attack succeeds. There is really no substitute for fixing this in the context of the message itself. Anything signed, should mention the person addressed in the text of the message. Example: message [1] =====[begin text of message to be signed and encrypted to Bob]===== Hi Bob, Thanks for everything! Love, Alice =====[end text of message to be signed and encrypted to Bob]===== as opposed to this, message [2]: =====[begin text of message to be signed and encrypted to Bob]===== Thanks for everything! Love, Alice =====[end text of message to be signed and encrypted to Bob]===== If at some later time, Bob and Alice had a falling out, Bob could send the second message to John, (a not so good friend of Alice). who now thinks Alice 'loves' him. Bob could obviously never do this with the first message in the above example. Again, more of an issue to be put in an advisory caution in the new rfc, rather than designing a new packet, but if the new packet is easy to implement, then great. vedaal From nobody Tue Mar 6 00:46:33 2018 Return-Path: X-Original-To: openpgp@ietfa.amsl.com Delivered-To: openpgp@ietfa.amsl.com Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 71581126BF0 for ; Tue, 6 Mar 2018 00:46:32 -0800 (PST) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -1.9 X-Spam-Level: X-Spam-Status: No, score=-1.9 tagged_above=-999 required=5 tests=[BAYES_00=-1.9] autolearn=ham autolearn_force=no Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id w_oyrR8_SAlB for ; Tue, 6 Mar 2018 00:46:30 -0800 (PST) Received: from mail.mugenguild.com (mugenguild.com [5.135.189.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 8D013120724 for ; Tue, 6 Mar 2018 00:46:30 -0800 (PST) Received: from localhost (62.43.79.238.dyn.user.ono.com [62.43.79.238]) by mail.mugenguild.com (Postfix) with ESMTPSA id 1B73D5FAAE; Tue, 6 Mar 2018 09:46:28 +0100 (CET) Date: Tue, 6 Mar 2018 09:46:25 +0100 From: Vincent Breitmoser To: vedaal@nym.hush.com Cc: openpgp Message-ID: <20180306084625.GA1078@calamity> References: <20180305231951.GA21944@calamity> <20180306040927.C83C66010D@smtp.hushmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180306040927.C83C66010D@smtp.hushmail.com> Autocrypt: addr=look@my.amazin.horse; keydata=mQINBFAB3UABEADCyB/vbIBA3m1Bwc yjTieEMLySwYgt54EQ2hglOocdtIhqC+b05t6sLSkwx2ukxrU2cegnCBkdyF/FZ/+Et638CUEBbf 4bjplwpt2IPLazQgjkwjMuhz0OcYDpMhwimTvh3mIl+0wzpOts6mEmMw0QZdl3RXvIW+NSynOn7q mz/fAv4Htt6lv2Ka0s6R2voyi+5U7CcIqizPad5qZVn2uxmovcFreTzFt6nk37ZbbTfvA3e5F0bR RQeH3viT5XxpJF4Y76v/Ua+5N3Kd18K0sX85rD1G7cmxR2CZ5gW1X24sDqdYZdDbf10N39UIwjJH PTeuVMQqry792Ap0Etyj135YFCE0loDnZYKvy2Y1i0RuEdTUIonIHrLhe2J0bXQGbQImHIyMgB9/ lva8D+yvy2gyf2vjRhmJEEco7w9FdzP7p3PhKrUiTjRsjHw8iV8LOCFx9njZOq9mism9ZZ16tZpx 9mXOf11HcH1RtVuyyQRS/4ytQPzwshXdSDDW6Btkmo9AbZQKC54/hSyzpp3Br2T2xDH7ecnonDB/ jv8rWuKXSTbX3xWAIrNBNDcTYaNe4jkms4HF7jJE19eRlqsXMMx6Fxvrh4TtKICwJYJ3AUmXrK3X Ti/mjqYfJ1fpBn54rWs8nhSR1fuZPD+aMlcP8BDUPlNKPKtj0DGSh3/VlnnwARAQABtClWaW5jZW 50IEJyZWl0bW9zZXIgPGxvb2tAbXkuYW1hemluLmhvcnNlPokCOAQTAQIAIgUCVTNZmgIbAwYLCQ gHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQe9GDIN6t+hHcVg//aeiijNqsQ3pjbFQn3VvND7hNfJ vrVcLZ+U4kOzXPF818aVdOnDyNXyE17vBDDcvaZ730sCsZIRZJ3KhUJ+nPvdttKjUIGLARmx+pA3 Jl3IIv2uLtOb3I0TMuyfIGJVGF+q10/CeDMKVjKlmyOVrR0opkel+KEoN7VLq3Hf3zPKENO1HBgp LHeP31tlb9cgs+u4o2wLrVe9myHbuFBW7EjWbSvdz2zliwbsFeFVLMNcWrKAU0GkkiH69SgnwmXU RkhGma4L27GLtkHHufsxfbcPqPtmtCttsGZU4EmrghGUqVyDOxnn8ZqybzLrRfpin+OCIX+aHJz5 r2L8qtrP0LorNMX3Gopd26vfhNvq/wq8xk++bW1R5FmkaUhx9h+DhO2ybcg7p/E8JHc8zrWv+bb3 0o9lkrOaU8GxXrgtb1cjtbb+MxFvjm0Elw7MSZDG7sF/APFU6cwuIA9Nai/OGAUCSt/W2ecS8Zox cWWbGSEiDvjtEctkpmHjfVuGoL34966Olm41VdH+NjgoSYUJKx4Mty8DRcZxdyoXll84LvDkEEYK ZqOIACsJf8CDFvUkmhXc+moCj15Yxtj3/RslRVEiOUyrpDwB72zWcZG8YnzoyGxhcRIc/gFejO/y SI8bzCpYngeuTb5NjFG+ChGiInHbQcFeHBlaHtKi2o/B5axIO5Ag0EVDvOgQEQALJby/ztliToGE u1lslvWQUQ6teKZVUQ7hy9bM4N83G0AGLatUBHtY6PkJBe4XkIw3sK7LoFCV2W4GSt4zWp9l+kG3 /J8Ow7EFjN0F7DrCg0M0lMg9dQz9jYSoBR8skaH3BRzCq9AKIVKV94poL/G65289L7zKDHoZnnyF qbBtedYZir0SZx+kiouZ1qnmxRPaYmH2fkuiuvYEAyzLDLYM8F5gQhdZM4YVtuvSICYPet0z4CDi JX/vZmDi3AzzoEVaKeAM/0H9f9Ni547J2+8dZSllgTrA+fq0aMJVScAObIxTAQtEq0DoNBzPpVrm W10b4bmgePrAvNkifqSr5StymSBgwvoeW6GrJiyN4XhoLOadZzwgjqioR1nXw5tXtrr5sYdkZ06b 1WWHkxtu1hFTdLC7RYNxY07ytLNM+C2lplCwCwlWB7RwI9BL1Dhre4kv8uaaX2Gksaq9mDf9MSDW qQ0TJ/RAiwMGmFrzBEYI1J2Oyeshi/dqW4/OiZAukOIlxOnt6u8zU2KL6Qjxqqna0oTbS4Zv3fRd YkuUCL6CDEJdkuRAiW+Gw+lKcMjXqApEqixhaDkoB/kwtu+2gIFTzAxMfwFN1YtNc0kJZWnFkGIW MrrwTcOwAFzlFz7wn/EyMFtg+ERcqMX0+olXDwM8MODI2+BzulPuEDEteCw09hABEBAAGJAh8EGA ECAAkFAlQ7zoECGwwACgkQe9GDIN6t+hFjuQ//UQyg49f8TytUYQaBb8R0UfI+KhQFs1Nsz2z8a3 0CD1MeiHHYWdAcomVvTkg4g5LbnYHVDrj/XagY3FN/AIE97usFbsTG+rsWAOLi7N2dN2ehWZ634k MvrgyC9uTiOdkw31+B8K5MpyySgD8e6SAzRfiu06/bcQOUyJifw8Hudpj9by4uyGhSH+kHu4afrp OduUighbsGFtcuRwwQ/w/oSk68XvPUgiOQWMZh/pVoXdFyFvrt/hgArCi8dfy5UPK58nl7jPnu/I uQXrJ50nNAFIIxPVeo2/B83KAnEZPU+qWZsdba0V+FIIQQVizLtQFMuJJk4/UTAOfJ2tBpQ9PADX 6/scqDE7unXNWdxcHTjK7KmWjXC8CyhGOx8V/rb7Ial4mZo4cTED6SNlO7dV1XYwnSctL2HCYNM3 RUe4eJ7JWuu7/Nbf6yip2eq7BQKZ9hAH/se/OSZNYsEkZ4pxUc8W5U3uAZImUwC6L74SM0jBZIuD mQhOYX6sZZ6urIn/MYlj4/hqSBFS4vTK7nXRLmtr7+5T5U5srVseUiYc+l9pu9/XD8zGIu+M2xEd 41NwP44GDQTQm0bFljRv5fSblwmi56YHPFQUIh2RZNX3kOJgeyQ3enw5uY+7ocKRVP38hpnffliL lJcO6TtHWnElS3pACbTQM0RHJox3zqU3q6K3c= User-Agent: Mutt/1.9.1 (2017-09-22) Archived-At: Subject: Re: [openpgp] Intended Recipient Fingerprint signature subpacket X-BeenThere: openpgp@ietf.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: "Ongoing discussion of OpenPGP issues." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 06 Mar 2018 08:46:32 -0000 > But, the attacker could still send it along as a clearsigned message, > and if the recipient accepts the message at face value, the attack > succeeds. That's correct. It *would* be possible to use the same subpacket even in a cleartext context, but that is a much less clear-cut use case that is more difficult to reason about, and easy to mess up in implementation. > =====[begin text of message to be signed and encrypted to Bob]===== By your other description, I assume you mean clearsigned messages here? For encrypted messages, the attack will fail: Bob can't forward a signed+encrypted message of Alice's to John and trick him into thinking it was intended for him, since the signature does say it was meant for Bob. > if the new packet is easy to implement, then great. For a typical workflow, it's very easy to implement. If you consider an api that is roughly: signAndEncryptTo(cleartext, signingKey, recipientKeys) -> ciphertext decryptAndVerify(ciphertext, decryptionKey) -> verificationstatus, cleartext then it works transparently from an api user perspective, and uses only information that is readily available in the implementation for an additional error case. - V