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An additional mode of key distribution in MIKEY

An additional mode of key distribution in MIKEY. draft-ignjatic-msec-mikey-rsa-r-00 D. Ignjatic, L. Dondeti, F. Audet. Public key in MIKEY (RFC 3830). MIKEY Public key mode requires initiator to have responder’s Public key (PKr) before sending the I_MESSAGE.

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An additional mode of key distribution in MIKEY

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  1. An additional mode of key distribution in MIKEY draft-ignjatic-msec-mikey-rsa-r-00 D. Ignjatic, L. Dondeti, F. Audet

  2. Public key in MIKEY (RFC 3830) • MIKEY Public key mode requires initiator to have responder’s Public key (PKr) before sending the I_MESSAGE Initiator Responder I_MESSAGE = HDR, T, RAND, [IDi|CERTi], [IDr], {SP}, KEMAC, [CHASH], PKE, SIGNi ---> R_MESSAGE = [<---] HDR, T, [IDr], V PKE = E(PKr, env_key) KEMAC = E(encr_key, IDi || {TGK}) || MAC

  3. Problem description • Very often, one does not have the PKr in advance, especially for peer-to-peer communication such as SIP • Certificate of responder may not be known in advance • Can not use MIKEY Public Key mode • Responder may have different identity than one originally called • Calls may be made to “group aliases”, phone numbers for hunt groups, etc. • “Forking” or “retargeting” (SIP for “forwarding”) • Can not predict who will answer • Will result in multiple round-trips • You may still want to do media encryption (sRTP) in those cases

  4. Proposed solution • New MIKEY Mode • Responder generates TGKs and PKE Initiator Responder I_MESSAGE = HDR, T, CERTi, [IDr], [SP], SIGNi --> R_MESSAGE = HDR, T, RAND, IDr|CERTr, {SP}, KEMAC, PKE, SIGNr PKE = E(PKi, env_key) KEMAC = E(encr_key, IDr || {TGK}) || MAC

  5. I_MESSAGE • Presents public key/cert of initiator to responder • Includes Timestamp (T) for replay protection • Responder’s Identity (IDr) optional • Indicating who initiator is interested in talking to • I_MESSAGE signed (SIGNi) to protect against DOS • Entire MIKEY message

  6. R_MESSAGE • Full roundtrip to download TGKs • PKE encrypted with Initiator public KEY (PKi) • KEMAC includes encrypted Identity of responder (IDr) & TGKs, plus a Message Authentication Code (MAC) • Also includes responder CERTr or IDr if there is reason to believe that CERTr is already provided using other means

  7. Other • Initiator may decide to proceed or not by based on identity/certificate of responder • New mode especially useful when expecting retargeting, forking, etc. • When you still want media encryption (sRTP) • Traditional mode useful when NOT willing to accept retargeting (i.e., when only wishing to reach a specific known user)

  8. Use of MIKEY-R with multicast MCServer Client Announce session (T,CSB ID) sent as multicast or out of band RSA_R I_MSG unicast RSA_R R_MSG unicast KMGT Done Multicast session (group TEK)

  9. Conclusion • Open issues • Describe multicast conferencing • Describe 3-way calling with identical media steams • Proposal: • Accept new MIKEY mode as working group document

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