RE: iSCSI: Decimal encoding - why 64 bits ?

[Paul Koning <ni1d@arrl.net>]

Excerpt of message (sent 3 July 2002) by Black_David@emc.com:
> Replying to a couple of messages on this topic.
> 
> --- Use of decimal for binary items
> ...
> > 4.1
> > binary-value includes regular-binary-value and large-binary-value.
> > regular-binary-value is for strings less than 64 bits and allows decimal
> > encoding. (It says less than 64 and decimal encoded binary strings are
> > always in bytes so the largest decimal encoded binary would be 56 bits.)
> > 
> > 10.4 SRP: N,g,s,A,B,M and H(A | M | K) are binary-values
> > 10.5 CHAP: C and R are binary-values
> 
> The only ones of these that should routinely fit in 64 bits are SRP's
> g (usually a small integer, even though it's mathematically a member of
> a very large binary field - I think Paul Koning missed the fact that
> generators tend to be single-digit numbers) and s (doesn't need to be
> a large number to get the job done). 

You're right about g.  As for S, it's the result of an exponentiation
modulo N, so it's no more likely to be a small integer than the other
SRP intermediate values.  Note that values supplied by the other end
are involved (as in conventional D-H) so you don't have the ability to
constrain your implementation to produce small S values.

In other words, S, A, and B will be bignums with probability
essentialy == 1.0, and allowing them ever to be encoded other than by
the large-binary-value rules is a waste of effort.

    paul