Register Reassignment

Created the Saturday 23 March 2019. Updated 6 months, 2 weeks ago.

Register reassignment is a technique used in code obfuscation and anti-disassembling to make reverse engineering and analysis more difficult. It involves modifying the instructions in a program to use different registers in different versions or instances of the program. This can make it more difficult for a reverse engineer or disassembler to understand the program's behavior, as the register assignments may not be immediately apparent or may change over time.

This technique is often used in malware to evade detection and analysis by security tools, as it can make the code more complex and less predictable. By switching registers in different versions of the code, the malware can evade signature-based detection techniques and make it more difficult for analysts to understand and analyze the code.

Technique Identifier

U0203

Technique Tags

Code obfuscation Register modification Code complexity Signature evasion

Code Snippets

Description

In this code, the registers eax and ebx are initially assigned to 0. The code then performs some operations on the registers, adding 1 to eax and 2 to ebx.

Next, the code reassigns the registers by copying the value of eax into ebx and the value of ebx into eax. This means that the value of eax will be the same as the original value of ebx, and vice versa.

Finally, the code performs more operations on the registers and returns the result. Because of the register reassignment, the final values of eax and ebx will be different than if the registers had not been reassigned.

This code is intended to be difficult to analyze and understand, as the register reassignment makes it more difficult to track the values of the registers. This can make it harder for a reverse engineer or disassembler to understand the code's behavior and intentions.

; Initialize registers
mov eax, 0
mov ebx, 0

; Perform some operations on the registers
add eax, 1
add ebx, 2

; Reassign the registers
mov ebx, eax
mov eax, ebx

; Perform more operations on the registers
add eax, 1
add ebx, 2

; Return the result
ret

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

https://sensorstechforum.com/advanced-obfuscation-techniques-malware/