Re: Magic Numbers in MD5

["Mark M." <markm@voicenet.com>]

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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
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