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</o:shapelayout></xml><![endif]--></head><body lang=EN-AU link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>We shouldn’t need another secret.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I had forgotten about OIDC Core §10 “Signatures and Encryption” where use of client_secret (after hashing and truncating) as an encryption key is explicitly defined. That removes the downside mentioned earlier for option 2. Option 2 would reveal the New OP’s client_id (issued by Old OP) to all the RPs, but that shouldn’t be an issue.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Reusing (the truncated hash of) client_secret to encrypt porting messages, in addition to encrypting and decrypting other OIDC messages (id_token, UserInfo response, requests, client auth) would be fine if only JWT had a proper way to unambiguously define the semantics of a message!<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>How about option 2 with "iss":<i>new_op</i>, "sector_id", "cty":"oidc-porting", and "kid":<i>client_id</i> in a JWE header and a string from the Old OP ("port_token_plain" value) as the payload?<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>--<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>James Manger<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='mso-fareast-language:EN-AU'>From:</span></b><span lang=EN-US style='mso-fareast-language:EN-AU'> Torsten.Lodderstedt@telekom.de [mailto:Torsten.Lodderstedt@telekom.de] <br><b>Sent:</b> Wednesday, 21 September 2016 1:25 AM<br><b>To:</b> Manger, James <James.H.Manger@team.telstra.com><br><b>Cc:</b> openid-specs-mobile-profile@lists.openid.net<br><b>Subject:</b> AW: Account porting: how to encrypt<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=DE style='color:#1F497D'>Hi James,<o:p></o:p></span></p><p class=MsoNormal><span lang=DE style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>do you think this function is worth managing another secret? What about using the new OP’s private key to additionally sign the package containing the porting token?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>best regards,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>Torsten.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=DE style='font-size:10.0pt;font-family:"Tahoma",sans-serif;mso-fareast-language:DE'>Von:</span></b><span lang=DE style='font-size:10.0pt;font-family:"Tahoma",sans-serif;mso-fareast-language:DE'> Openid-specs-mobile-profile [<a href="mailto:openid-specs-mobile-profile-bounces@lists.openid.net">mailto:openid-specs-mobile-profile-bounces@lists.openid.net</a>] <b>Im Auftrag von </b>Manger, James<br><b>Gesendet:</b> Dienstag, 20. September 2016 06:27<br><b>An:</b> <a href="mailto:openid-specs-mobile-profile@lists.openid.net">openid-specs-mobile-profile@lists.openid.net</a><br><b>Betreff:</b> [Openid-specs-mobile-profile] Account porting: how to encrypt<o:p></o:p></span></p></div></div><p class=MsoNormal><span lang=DE><o:p> </o:p></span></p><p class=MsoNormal>The current idea for account porting is for the Old OP to provide a single token (which I’ll call port_token_plain) to the New OP; the New OP encrypts it (for the Old OP) before passing the ciphertext (port_token) to an RP; the RP passes it onto the Old OP; the Old OP decrypts it to retrieve the original token and returns the RP-specific subscriber id to the RP.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The per-RP (actually per-sector-id) encryption is necessary to preserve the privacy of pairwise subs.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>An open question is how to do the encryption.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Option 1: public key and algorithm from Old OP metadata.<o:p></o:p></p><p class=MsoNormal>The port_token seen by an RP could be a JWE (compact encoding?).<o:p></o:p></p><p class=MsoNormal>One downside is that the encryption does not authenticate that is was done by the New OP.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Option 2: symmetric encryption with secret shared by the New OP and Old OP (such as the New OP’s client_secret used in calls to Old OP).<o:p></o:p></p><p class=MsoNormal>The port_token seen by an RP would be the ciphertext from an AEAD algorithm, keyed with the client_secret, using the iss and sector_id in the additional authenticated data.<o:p></o:p></p><p class=MsoNormal>This approach saves a few bytes, avoids some public key crypto, and avoids a metadata lookup to get a public key. A downside is that client_secret is not designed to be used as an AEAD secret key.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Any preferences?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='mso-fareast-language:EN-AU'>--<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-AU'>James Manger<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>