iSCSI: nits on SRP text key lengths

[Paul Koning <ni1d@arrl.net>]

The current draft talks about the length of the various binary data
keys used with SRP.  The length limit is given as 1024 bytes, i.e.,
8192 bits, for all of the binary data items.

8192 makes sense only if we allow a field modulus of that size, which
doesn't make a whole lot of sense.  If the groups are limited to those
defined in IKE, then the size limit becomes 1024 bits = 128 bytes.  If
the groups defined in the ips-security draft are also allowed, then
the size limit is 2048 bits = 256 bytes.

The H(...) key in SRP is a SHA-1 hash output, which means its size
must be exactly 20 bytes.

     paul