James Fator

74 to 75

03 April 2013

I have a program that when launched, opens a welcome prompt that I’m not a fan of. I took an assembly class last quarter and decided to give a go at disassembling the binary file and seeing what I could do. After a little searching, I determined that the creation of the launch window boiled down to a line of code that performed a jump if zero (“jz”). The x86 instruction set gives the jz instruction a value of 74 and bumping that value to 75 gives us the instruction for jump if not zero (“jnz”). We now have a successful binary that has no introductory prompt! I don’t know how often I’ll get the chance to do this in the future, but it sure was an experience.