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<p class="MsoNormal">We held two back-to-back sessions today at IIW (after lunch in space E) intended to produce consensus positions on JSON Web Tokens, including signing and encryption. Substantial consensus emerged, which is described in the notes below.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">These consensus decisions were in place by the start of the session:<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>There is an envelope (a.k.a. header) that completely describes the cryptographic algorithm(s) used<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>There is a payload (a.k.a. body) that is distinct from the envelope<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>There is a signature that is distinct from the envelope and payload<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Base64url encoding without padding is used to encode the parts above<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>The compact token representation separates the three encoded parts above by periods<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>No line breaks or other whitespace may be present in this representation<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Encryption must be supported as well as signatures<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>The token representation should be compact<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>In particular, this means that multiple base64url encodings of the same content should be avoided<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Any need for canonicalization should be avoided<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Open issues identified at the start of the session were:<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Ordering of the fields<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Ordering of the signing and encryption operations<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>What can be in an envelope (a small fixed set of things or is it extensible)?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>What to sign (envelope.payload or just payload)?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>What can be in the payload (only JSON token objects or arbitrary base64url encoded byte streams)?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Do we need to support multiple signatures?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Should we specify a JSON serialization as well as a compact serialization?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">These issues were resolved as follows:<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Ordering of the fields<o:p></o:p></p>
<p class="MsoNormal">By a vote of 8 to 1, people preferred the ordering envelope.payload.signature over the ordering signature.envelope.payload. Two reasons were cited: First, this allows for stream-mode operations, where consumers can begin operations based
upon the contents of the envelope before the signature has arrived without having to buffer the signature, and where producers can compute the signature in parallel with the transmission of the envelope and payload. The counter-argument advanced by Paul Tarjan
of Facebook (in abstentia) is that all languages have a string operation to split a string on the first occurrence of a character.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Ordering of the signing and encryption operations<o:p></o:p></p>
<p class="MsoNormal">How to compose these operations depends upon scenario requirements. Goals identified include Integrity, Confidentiality + Integrity, and Non-Repudiation. Paul Hill identified four sets of relevant operations, which were public key signature,
symmetric key MAC, symmetric key confidentiality + MAC, and key wrap/key transport/agreement with Diffie-Hellman. Some took the position that we should define a small set of fixed configurations that are known to safely achieve the intended goals; others
argued for general composability of operations. This was the one topic that we had to defer to a follow-on session to be held tomorrow, due to time limitations.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>What can be in an envelope (a small fixed set of things or is it extensible)?<o:p></o:p></p>
<p class="MsoNormal">We reached a consensus that the envelope needs to be extensible (but should be extended only with great care).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>What to sign (envelope.payload or just payload)?<o:p></o:p></p>
<p class="MsoNormal">Given that the envelope is extensible and therefore may contain security-sensitive information, we reached a consensus (with input from Ben Laurie via IM) that the combination envelope.payload must be signed.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>What can be in the payload (only sets of JSON token claims or arbitrary base64url encoded byte streams)?<o:p></o:p></p>
<p class="MsoNormal">By a vote of 9 to 2, the group decided that the spec should support signing/encrypting of arbitrary base64url encoded byte streams. They also decided that the spec should define the syntax and semantics of a set of claims when what is
being signed is a set of JSON claims.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Do we need to support multiple signatures?<o:p></o:p></p>
<p class="MsoNormal">The group voted 5 to 2 that it must be possible to support multiple signatures in some manner. Two variants of multiple signatures were discussed: the “gateway case”, where additional signatures are added to a token as it is passed between
parties, and the parallel case, where multiple parties sign the same contents up front. However the group also decided that it would be overly complicated to support multiple signatures in the compact serialization. Support for multiple signatures was pushed
to the JSON serialization (per the next issue).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Should we specify a JSON serialization as well as a compact serialization?<o:p></o:p></p>
<p class="MsoNormal">The group decided by a vote of 11 to 1 that there were use cases for a JSON serialization, and that multiple signatures would be possible in that serialization. The syntax agreed upon simply uses the three base64url encoded fields, while
allowing there to be parallel arrays of envelopes and signatures. Specifically, the syntax agreed upon was:<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.25in">{“envelope”:”[“<envelope 1 contents>”,…,”<envelope N contents>”],<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.25in">“payload”:”<payload contents>”<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.25in">“signature”:[“<signature 1 contents>”,…,”<signature N contents>”]<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.25in">}<o:p></o:p></p>
<p class="MsoNormal">and where each signature <i>i</i> is computed on the concatenation of <envelope
<i>i</i> contents>.<payload contents>.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ll follow this note with notes from the planned encryption session tomorrow.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> -- Mike<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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