downloadbrowseso61pi's KeygenMe#1

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This crackme use RSA algorithm.

MODERATOR NOTE: bonus challenge: produce only serials that are normal ascii printable characters

Difficulty: 2 - Needs a little brain (or luck)
Platform: Windows
Language: Assembler

Published: 27. Sep, 2009
Downloads: 611


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Solution by bLueDarK, published 05. oct, 2009; download (334 kb), password: or browse.

bLueDarK has rated this crackme as awesome.

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Discussion and comments

29. Sep 2009
hard for 2 lvl, i think solved only are brute
29. Sep 2009
:] brute force is not need.
30. Sep 2009
U win, I SURRENDER!. good crackme, but is so hard! If any have solution.. i need XD.
02. Oct 2009
i sent a keygen for this keygenme.. i used table system.. you can try to use different system..

good luck
02. Oct 2009
04. Oct 2009
05. Oct 2009
lol, so tell me how do you decode an algortihm, that uses MOD?

lets say
x mod 30 = 5
whats x?

x { 30*n+5 }
for x you will need the n component, which is impossible to reconstruct

i ask you this because there is a part where mod is used:
look at 0x4011A5

there is only one way - brute forcing the serial :P

best regards ;)
05. Oct 2009
@Lone.Wolf: you are right that the linear equation you wrote has infinite solutions (the congruence class is infinite)... but address 4011A5 is continually subtracting (calculating the modulus) instead after EXPONENTIATION by 0x9D - and mod carefully chosen numbers, it is invertible: read
05. Oct 2009
"and mod carefully chosen numbers, it is invertible"

thats magic ^^
i will familarize myself with rsa
thanks for the information

best regards
05. Oct 2009
i read that document before wrote a tuto.. but the 0x9D made it different... this is the reason why i didn't use the rsa decode system.. but i developed my own calculating system.. you know the name's total result.. and you can use it to calculating serial... at first i wrote all printable char and coded with serial algorithm.. for exmp. 1==>31h ----after serial algo---->24h
u==>75h ----after serial algo---->68h

i created a table about it.. and than i started to select char for that result..

if name's result is B0h we can generate serial many diffirent kinds..
similar this: 1u1,11u,u11; or another chars...

but we had a problem... we didn't have 01h's provision in table... therefore i allocated table odd and even.. if result is even i use even table, if result is odd i use odd table..

after the this change the result has never been 01h (:

at the and you don't use brote-force system cause it isn't necessary ((:
01. Feb 2010
This crackme has a bug.
Name="³³³³³³³³" -> Serial=Nothing

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