moctf reverse the first question: SOEASY

This is a 64-bit software, the OD open, with only IDA64 open, direct search string (shift + F12) can be seen

Reverse moctf second question: jumping jump

The problem had to reverse the beginner great sense of accomplishment I was studying the change instruction blasting, would not analysis algorithm, which can make a question still very comfortable

Open the program, is a guessing game

Loading search string OD

Double-click to see with the past, very clear, and that is the key jnz, just let realize the jump to the right

It directly to him out of it NOP

Save it

Just enter, eventually can successfully come out flag

This falg is base64 encryption, before submitting here many times always wrong, only to find later tried encodes

moctf Reverse third question: crush distress

But at that time I took a very hard time to understand this pseudo code (do not know yet Kan Bukan have to understand), went smoothly this time with OD analysis, but also spent more than an hour ......

First look at the process:

Loading OD, acquired by the input string to find a place, where the following program indicated by the arrow in FIG running waiting for input

It can be seen after the emergence of a CALL encrypted string, it would follow up this look at CALL

After you'll have to enter in order to find a CALL program algorithm (program is a word a word encrypted all converted just started will enter uppercase)

Program algorithm:

1. Take the characters one by one, transferred to uppercase, and then subtract 41 (hex) in the form of ASCII codes in uppercase results obtained (hex)

2. uppercase key then adding the result obtained

PS. Here do some processing, if coupled with later results exceeded capital letter Z (0x5A), it will be minus 19 (hexadecimal)

However, there is a problem, I found the ciphertext length is longer than the given key, how to do? I remember before watching the writeup says the key recyclable, namely: ilovemoctfilovemoctf, has been ranked so go on, no matter how much extra can ciphertext encrypted

To test this, I did an experiment

The number of such input plaintext keys and more than one, and more is the same as the first, we look at the cycle that is not in accordance with the