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malfunction
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 Posted: Thu Feb 28, 2008 10:43 am Post subject: Basic x86 ASM Mainly Term Explanations |
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So heres just a small overview on ASM, mainly the basic terms you should know before starting to crack.
Note this is x86 ASM
x86 ASM does not use 32 or 64 bit registers, only below 32, eg. 16, 8, 4,etc..
Please do correct me if I'm wrong in something, I'm not a master in ASM 
What you need to know to crack?
You need to know basic terms in assembly and some knowledge on hex values which the jumps will do. You must also have some programming knowledge in C or VB for coding KeyGenerators.
You will also need a good working brain along with certain tools ( mainly three tools ) mentioned in my tutorial on Serial Fishing (1st one)
Here are some of the terms in ASM (Assembly) and explanations
Registers
Registers are variables which are stored in your processor. The processor uses these variables for basic mathematical and logical operations. The mostly used registers are: eax, ebx, ecx and edx. Sometimes you may also see registers like edi, esi, esp, ebp.
Flags
Flags are Boolean variables (0 or 1 values). Flags are used by the processor for internal logical and mathimatical operations.
There are two important flags such as ZERO flag and NON ZERO flags.
Register Flags:
Abr//Name//Bit N//Description
| Code: |
OF Overflow Flag 11 indicates an overflow when set
DF Direction Flag 10 used for string operations to check direction
IF Interrupt Flag 9 if set, interrupt are enabled, else disabled
TF Trap Flag 8 if set, CPU can work in single step mode
SF Sign Flag 7 if set, resulting number of calculation is negative
ZF Zero Flag 6 if set, resulting number of calculation is zero
AF Auxiliary Carry 4 some sort of second carry flag
PF Parity Flag 2 indicates even or odd parity
CF Carry Flag 0 contains the left-most bit after calculations |
the Term Code
When you are analysing a piece of code, you must understand that the processor is actually quite simple, it simply follows the basic instructions, line by line.
Call
The syntax for a call should be like this
//SYNTAX//
.XXXXXXXX call ZZZZZZZZ // where .XXXXXXXX is the offset of the call and ZZZZZZZZ is the line no to be called
A "call" instruction calls the specified line number (here it is ZZZZZZZZ)
CMP
It means compare and it compares two registers. Its syntax must look like this
//SYNTAX//
.XXXXXXXX cmp eax,edx (or any other register)
Offset
Its quite simple to answer this one because it means a line number or address which appears in W32Dasm "@ Offset bla..bla..h"
where bla..bla.. is the offset and 'h' means hex.
Jump
A jump is an instruction which is very similar to a call.
W32Dasm
It is a disassembler/debugger which is used for disassembling programs.(both 16 bit and 32 bit windows programs)
For newbies w32dasm is recommended by most crackers.
HView (HackersView)
Its a hex editor and you can use this tool to modify the contents of the file.
There are many hex editors like hexworks, hexworkshop and free hex editor for windows.
Jumps//Explanation
| Code: | je jump equal >>>hex value is 74
jne jump not equal >>>hex value is 75
jnb jump not below >>>hex value is 73
jna jump not above >>>hex value is 76
ja jump above >>>hex value is 77
jb jump below >>>hex value is 72
jle jump lower or equal >>>hex value is 7E
jge jump greater or equal >>>hex value is 7D
jbe jump below or equal
jae jump above or equal
jnbe jump not below or equal
jnae jump not above or equal
jnge jump not greater or equal
jnbe jump not below or equal
jz jump if zero
jnz jump if not zero
jg jump if greater >>>hex value is 7F
jl jump if lesser >>>hex value is 7C
nop No-OPeration >>>It tells the program to "do absolutely nothing"
jmp jump directly to >>>this is an unconditional jump >>>hex value is EB
inc eax*** ==>>hex value = 40 ,
dec eax** ==>>hex value= 48 ,
nop* ==>>hex value= 90 |
The hex value for nop is 90.*
The "inc eax" means increase eax by one.***
The "dec eax" means decrease eax value by one.**
Thanks,
Sky
Originally Posted By: Skytactic
| Code: | | http://forum.astalavista.ms/viewtopic.php?t=122175 |
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Slugsnack
Grandmaster Cheater Supreme
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| Posted: Thu Feb 28, 2008 3:01 pm Post subject: Re: Basic x86 ASM Mainly Term Explanations |
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| skyllakarean wrote: | x86 ASM does not use 32 or 64 bit registers, only below 32, eg. 16, 8, 4,etc..
Please do correct me if I'm wrong in something, I'm not a master in ASM |
The majority of CPUs are 32 bit at the moment. This number is limited by either the size of the data bus or the largest general purpose register. In most modern CPUs, the address bus is 64 bits wide and the size of the largest GPR is 32 bits. There is a specific relationship between the 32 bit register and its corresponding 16 and 8 bit register.
For example, take EAX. EAX can hold 4 bytes/32 bits. The lower order part of EAX is AX, its 16 bit corresponding register. AX is then split into AL and AH, its higher and lower parts. Here is a diagram showing this relationship:
Btw by saying 80x86, you are describing the 80x86 instruction set which has no registers but is merely the set of instructions that can be used/are compatible with the 80x86 family.
| Quote: | What you need to know to crack?
You need to know basic terms in assembly and some knowledge on hex values which the jumps will do. You must also have some programming knowledge in C or VB for coding KeyGenerators. |
If you want to make keygens, any programming language will do. Most scripting languages will probably even do the job for you depending on how you go about getting the key.
| Quote: | Registers
Registers are variables which are stored in your processor. The processor uses these variables for basic mathematical and logical operations. The mostly used registers are: eax, ebx, ecx and edx. Sometimes you may also see registers like edi, esi, esp, ebp. |
They are actually part of the hardware on your CPU. They are essentially used because of their high performance. They have a fast access times, are very expensive so come in small quantities. Registers generally act as a "middleman" in every calculation.
| Quote: | Flags
Flags are Boolean variables (0 or 1 values). Flags are used by the processor for internal logical and mathimatical operations.
There are two important flags such as ZERO flag and NON ZERO flags. |
Not quite sure what you mean by non zero flag. There are many flags and they are held in the EFLAGs register as bits that can be toggled.
| Quote: | Register Flags:
Abr//Name//Bit N//Description
| Code: |
OF Overflow Flag 11 indicates an overflow when set
DF Direction Flag 10 used for string operations to check direction
IF Interrupt Flag 9 if set, interrupt are enabled, else disabled
TF Trap Flag 8 if set, CPU can work in single step mode
SF Sign Flag 7 if set, resulting number of calculation is negative
ZF Zero Flag 6 if set, resulting number of calculation is zero
AF Auxiliary Carry 4 some sort of second carry flag
PF Parity Flag 2 indicates even or odd parity
CF Carry Flag 0 contains the left-most bit after calculations |
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There is no register flag. The flags are held in a separate register to the ones you are talking about.
| Quote: | CMP
It means compare and it compares two registers. Its syntax must look like this
//SYNTAX//
.XXXXXXXX cmp eax,edx (or any other register) |
You can actually compare the following:
reg,reg
mem,reg
reg,mem
reg,imm
mem,imm
acc,imm
Yeah that's not bad, got a lot of good stuff there, keep it up 
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malfunction
Grandmaster Cheater Supreme
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Posts: 1015
Location: http://www.behindthecorner.com/
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| Posted: Fri Feb 29, 2008 7:49 am Post subject: |
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Thanks for correcting/completeing some of the stuff
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