Re: iSCSI base64 and 12-92

["Julian Satran" <Julian_Satran@il.ibm.com>]

I've lokked again at one of the most popular bignum packages - the one from MIT - and it seems to me that 
we are talking about two different things.

1. conversion from b64 to a binary number - and checking that it fits in the integer length you prealllocated
2. using a large integer
   
   
   1 is a trivial operation in b64 and is unrelated to the package you are using (if you are using one) and you will want to do it with the same code for large or small integer. At the end of this phase you should know if the number the size required by the protocol or not and you will have to do this test in any case
   And the conversion is not part of any packege i.e. if you decide not to use bignum arithmetic - and you are not mandated to implement it -
   the the conversion is just placing 6 bit values in predefined positions in an integer.
   
   2 Use of the large integer is an implementer choice - and if does not use bignum it does not have to fit in.
   
   In any case if we mandate b64 as being valid only for big numbers we have to check this and this is wasteful
   
   In summary - conversion must be done (for large numbers - as you don't know ahead of time how large the number used is going to be) and it is practically the same for small numbers. Then why check?
   
   And the bignum-packge itself you don't have to include it if don't implement large-number cryptography.
   
   Julo
   
   
   
   

   Paul Koning <ni1d@arrl.net> 05/23/2002 11:05 PM Please respond to Paul Koning

   To:        Julian Satran/Haifa/IBM@IBMIL         cc:        ips@ece.cmu.edu, wrstuden@wasabisystems.com         Subject:        Re: iSCSI base64 and  12-92

   
   
   Excerpt of message (sent 23 May 2002) by Julian Satran:
   > If base 64 is neede for large integers there is no good reason to test
   > that it is not used for short integers.
   
   Not true.  They are fundamentally different datatypes.  "short"
   integers are int, or long, or something like that.  Large integers are
   a software-defined datatype, typically an octetstring perhaps with
   additional control variables.  See any bignum package for the
   details.  
   
   The conversion routines used for these two are completely different
   and quite unrelated.
   
      paul