Just for the H@CK of it

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Mike Gonta

Joined: 26 Dec 2010
Posts: 241

Mike Gonta 10 Jan 2017, 23:36

Just for the H@CK of it here is an x86 (but not x64) executable signature which is essentially a nop in that it only
modifies the flags (but not the carry flag). An executable signature can be easily located and also run as code
without ill effect.

Code:

  db "H@CK"

disassembles as:

Code:

  dec ax ; 'H'
  inc ax ; '@'
  inc bx ; 'C'
  dec bx ; 'K'

The interesting thing is that the same register pair of inc / dec in close proximity to each other (they don't
necessarily have to follow each other, or be any particular order) will not normally be found in working code.
Because of this, really only the first two (or 4 in 32 bit) need to be located and the rest of the "word" makes
a nice "Easter Egg" for H@CKers disassembling the code.

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10 Jan 2017, 23:36

sleepsleep

Joined: 05 Oct 2006
Posts: 12229
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sleepsleep 12 Jan 2017, 09:48

online assembler wrote:

0: 66 48 dec ax
2: 66 40 inc ax
4: 66 43 inc bx
6: 66 4b dec bx

48,40,43,4b hex ascii is H@CK

very cool indeed, definitely not coincidence Idea

12 Jan 2017, 09:48

Mike Gonta

Joined: 26 Dec 2010
Posts: 241

Mike Gonta 12 Jan 2017, 10:05

sleepsleep wrote:

online assembler wrote:
0: 66 48 dec ax
2: 66 40 inc ax
4: 66 43 inc bx
6: 66 4b dec bx
48,40,43,4b hex ascii is H@CK

Actually, that's "fHf@fCfK".
In 32 bit asm it's:

Code:

  dec eax ; 'H'
  inc eax ; '@'
  inc ebx ; 'C'
  dec ebx ; 'K'

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12 Jan 2017, 10:05

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8268
Location: Kraków, Poland

Tomasz Grysztar 12 Jan 2017, 10:22

For 64-bit mode you may try this one:

Code:

db 'ASM['

Code:

0:  41 53  push r11
2:  4D 5B  pop r11

Or perhaps you can find something better?

12 Jan 2017, 10:22

Mike Gonta

Joined: 26 Dec 2010
Posts: 241

Mike Gonta 12 Jan 2017, 10:57

Tomasz Grysztar wrote:

For 64-bit mode you may try this one:
Code:
db 'ASM['    
Code:
0:  41 53  push r11
2:  4D 5B  pop r11    
Or perhaps you can find something better?

There's nothing better than this!

Code:

use32
  inc esi
  inc ecx
  push ebx
  dec ebp
  dec esi
  dec ecx
  pop ebx
  inc ebp

Code:

  db "FASM"

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12 Jan 2017, 10:57

sleepsleep 12 Jan 2017, 11:00

Mike Gonta wrote:

sleepsleep wrote:

online assembler wrote:
0: 66 48 dec ax
2: 66 40 inc ax
4: 66 43 inc bx
6: 66 4b dec bx
48,40,43,4b hex ascii is H@CK

Actually, that's "fHf@fCfK".
In 32 bit asm it's:
Code:
  dec eax ; 'H'
  inc eax ; '@'
  inc ebx ; 'C'
  dec ebx ; 'K'    

idk why the online assembler prepend 66 there, i tried another online assembler,

you are correct, definitely H@CK using xxd dump

Embarassed

just realize i am using ax and bx, Embarassed

my low end cheap processor Laughing

12 Jan 2017, 11:00

sleepsleep 12 Jan 2017, 11:06

Mike Gonta wrote:

Tomasz Grysztar wrote:
For 64-bit mode you may try this one:
Code:
db 'ASM['    
Code:
0:  41 53  push r11
2:  4D 5B  pop r11    
Or perhaps you can find something better?
There's nothing better than this!
Code:
use32
  inc esi
  inc ecx
  push ebx
  dec ebp
  dec esi
  dec ecx
  pop ebx
  inc ebp    
Code:
  db "FASM"    

wow! amazing!

12 Jan 2017, 11:06

Mike Gonta

Joined: 26 Dec 2010
Posts: 241

Mike Gonta 12 Jan 2017, 11:07

Mike Gonta wrote:

There's nothing better than this!
Code:
  db "FASM"    

Of course, to be fair to the "other" assemblers, these are just as good.

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12 Jan 2017, 11:07

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 19876
Location: In your JS exploiting you and your system

revolution 12 Jan 2017, 14:14

Mike Gonta wrote:

There's nothing better than this!

Code:

use32
  inc esi
  inc ecx
  push ebx
  dec ebp
  dec esi
  dec ecx
  pop ebx
  inc ebp

Code:

  db "FASM"

I get this: FASMNI[E

12 Jan 2017, 14:14

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