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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

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
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

problem description
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
proposed solution
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

i message
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
r message
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
other
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)
use of mikey r with multicast
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)

conclusion
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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