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Brute Force Algo In C And Asm

Guest K.PAZ

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Recently I was working on a crackme and I needed to bruteforce it.

Since I could not find a decent algorithm for creating strings from a character set, I came up with this 2 algo's in C and Assembler.

The algos are probably not optimized (the assembler one , for sure not), so if you have suggestions please go ahead and mail me.

Since I am still a beginner in this I will appreaciate every comment.

Algo in C


void BruteForce();char *CharSet = "abcdefghijklmnopqrstuvwxyz1234567890 ";
char a[32];//---------------------------------------------------------------------------
void BruteForce()
char finalDigits = 3; // number of digits minus 1 (here 4 "aaaa .... 0000")
char lenCharSet;
long End;
div_t x;
long l; lenCharSet = strlen(CharSet);
End = pow(lenCharSet,finalDigits+1);
for (long k=0; k<End; k++)
l = k;
for (int i=finalDigits; i>=0 ; i--)
x = div(l, pow(lenCharSet,i));//
a[i] = CharSet[x.quot];
l = x.rem;
// String is in a available


Algo in Assembler


SetLen equ 37
Digits equ 3 ; number of digits minus 1 (here 4 "aaaa .... 0000")
szSet db "abcdefghijklmnopqrstuvwxyz1234567890 ", 0 ; 37 zeichen
a db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0BruteForce proc
LOCAL wEnd:WORD; mov ecx,Digits ; length of Output
mov eax,SetLen ; length of characterset
imul eax, SetLen; ;AX = SetLen^Digits
loop Loop1
mov edi,eax
Loop_K: ; for (k=0; k<End; k++) k in EDX
mov ebx,Digits
mov edx,edi
dec edx
Loop_i: ;for (int i=Digits; i>=0 ; i--) i in EBX
mov esi,1
mov ecx,ebx ; check if ebx =0
test ecx,ecx
jz AfterPower ; if ebx = 0 ESI = 1 (SetLEn^0=1)
imul esi, SetLen; ;ESI=SetLen^i (ebx)
loop Loop2
test edx, edx ; if edx = 0 avoid div by zero Error
jnz NotNull
mov eax,0
jmp AfterNull
mov eax,edx
idiv esi ; div edi / SetLen^ebx
mov al, BYTE ptr [szSet+eax] ;a[i] = szSet[eax]
mov BYTE ptr [a+ebx],al
test ebx,ebx
jz EndLoop_i
dec ebx ;i--
jmp Loop_i
EndLoop_i: ; Here the string is available in BYTE a dec edi ;k++
test edi,edi
jnz Loop_K
BruteForce EndP




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