From: "Mark M." <markm@voicenet.com>
Date: Sat, 14 Dec 1996 11:43:10 -0800 (PST)
To: ph@netcom.com>
Subject: Re: Magic Numbers in MD5
In-Reply-To: <v02140b01aed7e51544ac@[192.0.2.1]>
Message-ID: <Pine.LNX.3.95.961214143723.587A-100000@gak.voicenet.com>
MIME-Version: 1.0
Content-Type: text/plain


-----BEGIN PGP SIGNED MESSAGE-----

On Fri, 13 Dec 1996, Peter Hendrickson wrote:

> I am curious where some of the magic numbers in MD5 originated.
> 
> First, we have the four chaining variables, A, B, C, and D which
> are initialized with apparently random numbers.  Are they as
> random as they look, or are they carefully chosen?

Random?

A = 0x01234567
B = 0x89abcdef
C = 0xfedcba98
D = 0x76543210

> Second, we have the t_i values.  Schneier's first edition says this:
> 
> "In step i, t_i is the integer part of 4294967296xabs(sin(i)), when
> i is in radians.  (Note that 4294967296 is 2^32.)"
> 
> Does abs(sin()) have some properties that are especially conducive to
> strengthening MD5 or is it just a function to generate mildly random
> numbers?  If the latter, wouldn't the algorithm be stronger if it was
> used with completely random numbers?

I am not sure of the properties of abs(sin()).  I know that the S-boxes in
Blowfish are initialized with pi.  I would guess that the purpose of using
such values is to use easily generated pseudo-random numbers.

Mark
- -- 
finger -l for PGP key
PGP encrypted mail prefered.
0xf9b22ba5 now revoked

-----BEGIN PGP SIGNATURE-----
Version: 2.6.3
Charset: noconv

iQEVAwUBMrMD/SzIPc7jvyFpAQEA7gf9HAtV1Vy+3LO5OPOHyU9ZHoath32LhAwU
PzODS/YJsY9fVxaMHOm15oL9D4CX2D5s/Y9cgrALG6pGzw4dBWJZJyqNAcbmsjp/
B/jNL9jXKCXg1byIzplKSjJqDypLzIPf07xTIQVCC5IDmwZ7pR5owngH9MDaE8is
aFiGZvuWNm7eHQg1kJSb40xQjkwszx+SP1Gv9+fvpys5GZLCTHwPx8SCpy7PXwNp
lm8fgV9mjc7wZIpw73oqPZEb7Q3VHZUOUXS2i6XNF3UVXa4aykBg5VvALPt0tuvv
ah5JjA6JP4STwSCj+HrnMpQJ8SCG4U3kKb54+WOl8H6eo7ekuEU8mw==
=uNLG
-----END PGP SIGNATURE-----