CrackMe® Practices for Newbies
Project 9: CrackMe 2 by Cronos

Re: Re: Re: Re: Re: Re: Joseph's Thread
Saturday, 03-Apr-99 04:49:44

    OK. What I am saying is that 2^16 and 5bf (=1471 decimal) are relatively prime, which is to say that gcd(2^16,1471)=1. Note that 2^16 itself is not prime, and 'relatively prime' just means that two numbers share no common factor.

    This is a short way of saying that the inverse of 1471 in a 2^16 modular system exists. In fact you will see that all odd numbers have inverses mod 2^16, and no even numbers have inverses mod 2^16. What I mean by an inverse of a number in a modular system is that there exists another number such that the product of the two is 1.

    Example:
    consider numbers mod 16, and specifically consider 9. Now 9 and 16 are relatively prime since gcd(9,16)=1. So the inverse of 9 exists mod 16. This can be found using the Euclidean Algorithm, the detail of which I won't go into here, but you can find it in just about any book on Number Theory. Suffice to say the inverse of 9 is in fact 9. So 9 is self inverse here.

    Cronos.


    Cronos


Message thread:

Joseph's Thread (Question to Cronos) (30-Mar-99 23:45:59)

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