Re: iSCSI: Authenticating with SRP

["Ofer Biran" <BIRAN@il.ibm.com>]

Ken,

The SRP login example in Appendix C was not updated
with the last change of using pre-defined group identifiers
instead of sending N,g explicitly, this should be corrected
in the first opportunity.

> and the second doesn't let the target provide a SRP_N or
> a SRP_g.

Both sides should know a-priory the N,g of the 'well known'
pre-defined groups, and they are not sent anymore on the wire.
(11.1.3 - "and G,Gn (Gn stands for G1,G2...) are identifiers
of SRP groups specified in [SEC-IPS]." )

 Regards,
   Ofer


Ofer Biran
Storage and Systems Technology
IBM Research Lab in Haifa
biran@il.ibm.com  972-4-8296253



                                                                                                              
                      Ken Sandars                                                                             
                      <ksandars@eurolog        To:       Julian Satran/Haifa/IBM@IBMIL                        
                      ic.com>                  cc:       ips@ece.cmu.edu, owner-ips@ece.cmu.edu               
                      Sent by:                 Subject:  iSCSI: Authenticating with SRP                       
                      owner-ips@ece.cmu                                                                       
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                      06/02/03 16:49                                                                          
                                                                                                              
                                                                                                              




Hi Julo,

When authenticating with SRP, I'm not sure exactly which parameters are
required. In particular, the example in appendix C conflicts with section
11.1.3.

Based on the example login transaction (Appendix C):

     I-> Login (CSG,NSG=0,1 T=1)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=KRB5,SRP,None

     T-> Login-PR  (CSG,NSG=0,0 T=0)
         AuthMethod=SRP

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_U=bob
         TargetAuth=Yes

     T-> Login (CSG,NSG=0,0 T=0)
         SRP_g=2
         SRP_s=0X12343456745ABCDS (well, lots o' hex digits)
         SRP_N=??????

In 11.1.3, the suggested sequence is:

     I-> Login (CSG,NSG=0,1 T=1)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=KRB5,SRP,None

     T-> Login-PR  (CSG,NSG=0,0 T=0)
         AuthMethod=SRP

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_U=bob
         TargetAuth=Yes

     T-> Login (CSG,NSG=0,0 T=0)
         SRP_GROUP=SRP-768,SRP-1024,SRP-1280,SRP-1536,SRP-2048
         SRP_s=0X12343456745ABCDS (well, lots o' hex digits)

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_A=0xABCDEF12345345354
         SRP_GROUP=SRP-1536

       ......


I don't understand this sequence, and neither does the initiator we are
playing with! ;-)

The first sequence doesn't negotiate the SRP_GROUP parameter, and the
second
doesn't let the target provide a SRP_N or a SRP_g.

Should the full sequence be (try 1):

     I-> Login (CSG,NSG=0,1 T=1)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=KRB5,SRP,None

     T-> Login-PR  (CSG,NSG=0,0 T=0)
         AuthMethod=SRP

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_U=bob
         TargetAuth=Yes

     T-> Login (CSG,NSG=0,0 T=0)
         SRP_GROUP=SRP-768,SRP-1024,SRP-1280,SRP-1536,SRP-2048
         SRP_s=0X12343456745ABCDS (well, lots o' hex digits)

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_GROUP=SRP-1536

     T-> Login (CSG,NSG=0,0 T=0)
         SRP_g=2
         SRP_N=0XABCD123132523453 (as per SRP_GROUP)

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_A=0xABCDEF12345345354

      .... and things proceed from here


However, this introduces an extra step which may be collapsed (try 2):

     I-> Login (CSG,NSG=0,1 T=1)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=KRB5,SRP,None

     T-> Login-PR  (CSG,NSG=0,0 T=0)
         AuthMethod=SRP
         SRP_GROUP=SRP-768,SRP-1024,SRP-1280,SRP-1536,SRP-2048

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_GROUP=SRP-1536
         SRP_U=bob
         TargetAuth=Yes

     T-> Login (CSG,NSG=0,0 T=0)
         SRP_g=2
         SRP_s=0X12343456745ABCDS (well, lots o' hex digits)
         SRP_N=0XABCD123132523453 (as per SRP_GROUP)

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_A=0xABCDEF12345345354

      .... and things proceed from here


Does this look right?

Thanks,
Ken





Ken Sandars
Eurologic Systems
Howard House
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Bristol
United Kingdom
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