picoCTF2018

2018-10-13 00:00:00 +0000

This challenge is give we a file like this:

This is a file ELF 32-bit LSB executable, ok..try run it.

The program is request a parameter . This parameter must lenght is 16 byte . So we need input 16 character for this file. if this input correct then program will show flag. Open file with IDA pro to see souce code. Found to main function

Summary program active : Firstly -> program will check parameter . if parameter < 1 program will show “Please Provide a VALID 16 byte Product Key.” else it will call check_valid_key(). This is check_valid_key() code :

The main purpose of check_valid_key() is check characters in the range “0”->”9” and “A” -> “Z”. Next validate_key() function:

The main purpose of this function is check sum of (key[i] * index+i) (i in range 0->14) then take compare sum % 0x24 with key[15]. if equal will show flag. Ok.. I writed a python script to show Product Key

Result:

picoCTF2018

2018-10-13 00:00:00 +0000

At this challenge , We have a file asm :

With three paramater for function asm3(0xb3fb1998,0xfe1a474d,0xd5373fd4). we have the stack frame will be like this:

Firstly, instruction mov eax,0x62 -> eax=0x00000062 -> al=0x62, ah=0x00

Next, xor al,al -> al=0 -> eax=0x00000000

Next mov ah,BYTE PTR [ebp+0xa] -> ah = 19 -> ax= 0x1900

Next sal ax,0x10 -> left shifts ax -> ax=0x0000

Next sub al,BYTE PTR [ebp+0xd] -> al = 0x00-0x47 = 0xb9

Next add ah,BYTE PTR [ebp+0xe] -> ah = 0x00+0x1a = 0x1a

Next xor ax,WORD PTR [ebp+0x10] -> ax=0x1ab9 xor 0x3fd4 = 0x256d

The result for this challenge is 0x256d

picoCTF2018

2016-10-15 00:00:00 +0000

This challenge is the same with challenge keygen me 1. It is just different at validate_key() function. Put it in to IDA pro , after find to validate_key() function. We have like this

Key will thought 12 function to check correct key . key_constraint_01()

key_constraint_02()

All function next the same with function 1 and 2. so I don’t show it at here. I will solve it with Z3. I writed a script to solve : The result:

Homework

2016-08-22 00:00:00 +0000

People’s opinions differ as to whether or not school children should be given homework. While there are some strong arguments against the setting of homework. I still believe that it is a necessary aspect of education.

Environment

2016-08-20 00:00:00 +0000

Humans are responsibale for a variety of problem environment, but we can also take steps to reduce the damging that we are causing to the planet. This essay will discuss emvironment problems and the measures that goverment and individuals can take to address these problem.

Two of the biggest threats to the environment are air pollution and waste. Gas emissions from factories and exhaust fumes from vehicles lead to global warming. Which may have a devastating effect on the planet in the future. As human population increases, we also producing ever greater quantities of waste. Which contaminates the earth and pollutes rivers and oceans.

The goverment could certainly make more effort to reduce air pollution.They could introduce laws to limit gas emissions from factories or to force companies to use renewable energy from solar, wind or water power. They could also impose “Green taxes” on drivers and airline companies. In this way, people would be encouraged use public transport and to take fewer flights abroad, therefore reducing emissions.

Individuals should also take responsibility for the impact they have on the environment. They could take public transport rather than driving. Choose products with less packaging, and recycle as much as possible. Most supermakets now provide reusable bags for shopper as well as banks for recycling glass, plastic, paper in their car parks. By reusing and recycling. we can help to reduce waste.

In conclusion, both national goverment and individuals must play their part in looking after the environment.