==========================================
Standalone DH1080 keyXchange script v1.25:
==========================================


Since some of you might not want to use FiSH addon and stay with the
blowcrypt script by sinner (or any other), it is still recommended to
use the new Diffie-Hellman 1080bit keyXchange feature! Which is now
available as a standalone mIRC script.

You DO NOT need this standalone script if you are using FiSH addon!


*IMPORTANT*
If you are using a very old blowcrypt script, which stores the keys
plain-text in the blow.ini use DH1080-P.mrc, else use DH1080.mrc ...


- Place FiSH.DLL and DH1080.mrc into same directory as mIRC.exe
  (Your blow.ini should be located in same directory and not something
  like mIRC/addons!)
- You DON'T have to patch anything!
- Load DH1080.mrc into mIRC (ALT+R, File->Load->Script)

- Make sure you have only ONE script (DH1080.mrc or DH1080-P.mrc) loaded!

- If you want to perform DH1080 keyXchange each time a new query window
  opens, enable 'Auto-KeyXchange' in the context menu.
  
  This will work for 'known' people, those you already had a key set
  for, but also if the opening query starts with "+OK" (encrypted, but
  no key set or nick changed).


Now go and make sure all your friends upgrade too :)



==============
Security Info:
==============

What happened to DH1024 key-exchange you may ask. To make it short: An
implementation flaw in the code has been found and a new key-exchange
using Diffie-Hellman 1080 bit has been introduced. The implementation
flaw is NOT about a remote vulnerability, it is rather about maths :)

The analysis of a friend has come to the conclusion: The old DH1024
key-exchange was probably still as secure as 991 bit. We cannot say
for sure. The characteristic of the implementation flaw makes it hard
to analyze, as not much material about this subject is available.

I was very angry when this problem was discovered, but I can't change
what happened now. Such a stupid mistake, unnoticed almost a year.
Well, everyone learns from mistakes ...


Make sure you NEVER exchange keys plain-text over IRC/ftp/email! If
you ever do that, or someone else who owns that key, you might aswell
just keep talking plain-text.
Use the new Diffie-Hellman (1080 bit) keyXchange function!

You might think this is crazy, but keep in mind: You are using IRC
encryption because you think someone might be able to read your
conversations. Such a person may not only have enough skills for
that, but also for defeating your weak encryption mechanism, including
passwords sent in plain-text and maybe even using DH-128.


While rewriting the Diffie-Hellman key-exchange, it was discovered
that the used 128bit numbers in DH.dll (written by sinner?) are not
nearly secure enough for key-exchange!

It would take just approx. 3 hours to calculate someones private key
by having only the transmitted public key, on a 1.7 GHz machine with
256 MB RAM!

Now half of the time is used for pre-computation, which needs to be
done only once. And from that point you can calculate any private key
generated with the DH.dll in only 1.5 hours!

This applies to *all* DH key-exchange plug-ins using 128bit keys! It
is suggested to use at least 512bit for Diffie-Hellman.


Therefore keyXchange with Diffie-Hellman in this addon was upgraded
to 1080bit. It is not compatible to the old DH keyXchange with 128bit!

The DH routines are now located in FiSH.DLL and have been completly
rewritten using MIRACL. (Thanx to mac for discovering the weakness of
DH128 and helping me!)



================
Technical notes:
================

For Diffie-Hellman key-exchange a 1080bit germain prime is used, the
generator g=2 renders a field Fp from 1 to p-1. Therefore breaking it
means to solve a discrete logarithm problem with no less than 1080bit.

Base64 format is used to send the public keys over IRC.

The calculated secret key is hashed with SHA-256, the result is converted
to base64 for final use with blowfish.


Some words about the used pseudo random number generator from the author:

"This PRNG is based on Serpent, SHA-1 and RIPE-MD 160. The way it is
designed it is as strong as Serpent-160 CFB. The two hashes are chained
in case of one hashes appears to have properties that makes its output
guessable. I did not chain two ciphers for performance reasons.

The implementation of the cryptographic algorithms have been tested
against test vectors. The hashes are optimized in assembly language
whereas Serpent uses the standard implementation compiled with ICC8.

How it works:
It initially gathers entropy from various system data and adds it to a
pool that gets hashed by SHA-1 and RIPE-MD 160. The pool is then hashed
(by SHA-1 & RIPE-MD 160) and a 160 bit Serpent key is then expanded.

While the program is running, it will make calls to a function of the
PRNG that uses a low level timer to add entropy to the pool. When the
pool is filled, it is mixed.

When you request random data to the PRNG, a buffer is ciphered with
Serpent in CFB mode. After a certain amount of generated bytes, the key
is considered "expired" and a new one is derivated from the hash of the
current pool.

The PRNG can save its state. It will save the pool, add entropy to it
and hash it. What is on disk is always different from what is in memory.
The next time it is started, it will load it, add entropy to it, and
hash it. If an attacker gains access to the PRNG state, the PRNG becomes
as strong as when no file was present."





Comments and suggestions are welcome!



Enjoy

20. April 2004