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  #1  
Old 10-27-2015, 12:30 PM
visions_of_eden visions_of_eden is offline
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Default Encryption Algorithm

Hi ,

i'm trying to reverse an encryption algorithm that takes and usigned integer and an index value and returns the encrypted / obfuscated 32 bit unsigned value .

The algo looks like :

Encrypt ( plain UINT32 , KEY_INDEX , OUT_VALUE)

the encrypt function takes the (KEY_INDEX % 0x64)*8 and ((KEY_INDEX % 0x64)*8)+8 from a 0x190 elements 4 bytes array , the plaintext value and calculates the cipher value using some kind of transformation function based on floating point calculations .

Does anybody have a clue on what encryption/obfuscation algo uses this king of behaviour .

It's quite difficult to extract the algo end reverse it so any help would be useful .

thanks .
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  #2  
Old 10-29-2015, 03:41 AM
visions_of_eden visions_of_eden is offline
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Default Solution Found

To reply to myself i found the soluton to the problem .

The ctypto function is a simple modular exponentiation function .

It choses a random MODULO and EXPONENT from a lookup table based on a chosen index then calculates X^EXPONENT MOD (MODULO) where X is the 32bit plaintext that we want to encrypt .

So theorically reversing the function should be fesible since the problem to solve is calculating the nth modular root of the result .
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  #3  
Old 10-29-2015, 04:51 AM
visions_of_eden visions_of_eden is offline
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Default Found

How dumb i am !!

Algo used was simply RSA using 32bit (tooooo week ) key .

Reversed .
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