Subj : FTS-1027 (BinkP 1.0 CRAM)
To : Rob Swindell
From : Alexey Vissarionov
Date : Thu Mar 08 2018 09:09 am
Good ${greeting_time}, Rob!
07 Mar 2018 18:52:54, you wrote to All:
RS> In the development of a new binkp implementation
RS> (
http://wiki.synchro.net/module:binkit), *we* came across a
RS> deficiency in the FTSC document: FTS-1027.
RS> Regarding this text:
RS> 1.3 Generating and Transmitting Challenge Data
RS> Size and contents of challenge data are implementation-dependent, but
RS> it SHOULD be no smaller than 8 bytes and no bigger than 64 bytes
64 to 512 bits... that resembles one pretty good cryptographic transform.
RS> Let it be known that the reference binkp implementation, binkd, has
RS> (apparently) only ever sent a 16 byte CRAM challenge (no more, no
RS> less)
IIRC, that's some random data whitened by MD5 hash function. Now MD5 is proven
to be unsafe(*), so the implementations should replace it with not-yet-broken
crypto-safe functions like SHA2 or Skein.
RS> and some implementations (e.g. Internet Rex) only work (succesfully
RS> authenticate) if the received challenge is exactly 16 bytes (no more,
RS> no less).
That's a bug. Have you reported it to the developers of those mailers?
RS> There's no mention of a 16 byte CRAM challenge (32 hex characters)
RS> in the specification, but 16 bytes appears to be exactly what all
RS> existing implementations actually send
8 < 16 < 64
RS> and probably all any implementation should *ever* send if they wish
RS> to be compatible will all known existing implementations.
What if they wish to be compatible with the published standard based on very
popular reference implementation?
RS> I just felt this should be documented, if it isn't already, by the
RS> FTSC.
Over 80% of all IBN-capable systems use binkd, so its' behavior still is the
current practice, which is exactly documented by FTSC.
(*)
Look at these two images:
http://pics.rsh.ru/img/md5_collision_image2_26j2eiqr.jpg
http://pics.rsh.ru/img/md5_collision_image1_5l7k706x.jpg
Now download them and compare their sizes and MD5 sums :-)
--
Alexey V. Vissarionov aka Gremlin from Kremlin
gremlin.ru!gremlin; +vii-cmiii-cmlxxvii-mmxlviii
... god@universe:~ # cvs up && make world
--- /bin/vi
* Origin:
http://openwall.com/Owl (2:5020/545)
