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    ²²  / __ \___ ___ _______ ___  ___/ /__ ____  / /____²² Û Û
    ²² / /_/ / -_|_-</ __/ -_) _ \/ _  / _ `/ _ \/ __(_-<²² Û Û
    ²²/_____/\__/___/\__/\__/_//_/\_,_/\_,_/_//_/\__/___/²² Û Û
    ²²                                                   ²² Û Û
    ²²      Web: http://www.ImmortalDescendants.com      ²² Û Û
    ²²                 Author: ACiD BuRN                 ²² Û Û
    ²²                Date: 09/01/2000                   ²² Û Û
    ²²         Topic: cracking TSCUBE's RSA CRACKME      ²² Û Û
    ²²               Level: intermediate                 ²² Û Û
    ²²                                                   ²² Û Û
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Crackme is here: http://www.infini.fr/~lkubaski/reverse/RSAcrkme10.zip


Introduction:

well , this crackme is RSA24 , so it is not that hard , but it is good to
familiarise with RSA stuff ...
I won't explain lot on how RSA works , but just explain how to reverse this crackme !
There is already some docs on RSA , like the Lucifer48 'n Crackz ones ...
you can find it at : http://www.multimania.com/lucifer48/ and http://www.wco.com/~micuan/


Tools needed: 

- Factor.exe (to calcul p and q when we know n) and ce.exe ... 
  url: http://134.155.63.117/~quantico/ghiribizzo/rsa/rsa.html

- abn.exe coded by TSCUBE, will be avaiable soon , i can't spread the beta version...

****************
* Basic of RSA:*
****************

p*q = n

We know n and we need to find p and q (p and q are primes numbers)
it is not evident when n=512 bits ..

How to get "p" and "q" when we got "n" ?
Well for this , i used "factor.exe"

let's look the crackme itself !
Desasm it and look in string data references ! we see some numbers :

12790891
5666933
8483678
9901
...

if we check the code in asm we see this:

* Possible StringData Ref from Data Obj ->"9901"       <-- e
                                  |
:004029CD 68DC004200              push 004200DC
:004029D2 8D8C24E4000000          lea ecx, dword ptr [esp+000000E4]
:004029D9 E852E7FFFF              call 00401130

* Possible StringData Ref from Data Obj ->"12790891"   <-- n (n > e so we know it is n)
                                  |
:004029DE 68D0004200              push 004200D0
:004029E3 8D4C241C                lea ecx, dword ptr [esp+1C]
:004029E7 C784246406000000000000  mov dword ptr [esp+00000664], 00000000
:004029F2 E839E7FFFF              call 00401130

* Possible StringData Ref from Data Obj ->"8483678"   <-- 1st uncrypted part of the serial
                                  |
:004029F7 68C8004200              push 004200C8
:004029FC 8D8C2474020000          lea ecx, dword ptr [esp+00000274]
:00402A03 C684246406000001        mov byte ptr [esp+00000664], 01
:00402A0B E820E7FFFF              call 00401130

* Possible StringData Ref from Data Obj ->"5666933"   <-- 2nd uncrypted part of the serial
                                  |



This crackme use RSA 2 times !
the final serial is the 1st crypted part + the 2nd crypted part , added as string

ok , enough blablabla , let's go


1st , we want to have "p" and "q" , fire up "factor.exe" ...
it show us how to use it:

C:\rsa>factor.exe

Usage: factor <number>
OR
factor -f <formula>
e.g. factor -f 10#100-19

To suppress the commentary, use flag -s
To input from a file, use flag -i <filename>
To input from a binary file, use flag -b <filename>
To output to a file, use flag -o <filename>
e.g. factor -f 10#100-7 -s -o factors.dat

ok so: factor.exe n


we do factor.exe 12790891 and we obtain this :


C:\rsa>factor.exe 12790891
first trying brute force division by small primes
PRIME FACTOR     1667
PRIME FACTOR     7673

ok, good !! now we have p=1667 and q=7673


We will need to calcul d now !
For this we will use ce.exe !

Fire up it and look :


Exponent Calculator v1.3 _ Ghiribizzo [OR&L/uKC] 1999

Usage: CE <p> <q> <e>

p=1667 and q=7673 and e=9901 (we have found "e" in string data reference)

let's enter this numbers:

C:\rsa>CE 1667 7673 9901

Exponent Calculator v1.3 _ Ghiribizzo [OR&L/uKC] 1999

Inverse Exponent:
10961333

so d=10961333 ...

ok, now we can finish our work !! we will cryp each uncrypted part of the crackme
to make our final serial !!
It is an serial only crackme , coz the name is not used for the calculation...

( uncrypted ^ d ) % n = serial !

As this crackme use 2 parts as serial here comes the caculation :


* 1st Part: (we use abn.exe for this calcul a=8483678 , b=10961333 , n=12790891)

(1st Message uncrypted ^ d ) mod n = 1st serial crypted

For us :

(8483678 ^ 10961333 ) mod 12790891  = 7167622 = 1st part



* 2nd part: (we use abn.exe for this calcul a=5666933 , b=10961333 , n=12790891)

(2nd Message uncrypted ^ d ) mod n = 1st serial crypted

For us :

(5666933 ^ 10961333 ) mod 12790891  = 3196885 = 2nd part


so the final serial is: Part1 + Part2 (added as string)= Part1Part2

The serial is: 71676223196885


Enter your name , this serial and we obtain:

Well done, ACiD BuRN ....
Great , we did it !!!!!