rev/awa-jelly

184 solves / 395 points

Writeup by Aryan

We are given a link to AWA5.0, a weird language consisting solely of awa's. Our job is to reverse engineer a certain output to figure out the input string. We are provided with the code.

Going to the AWA5.0 website, we can put in a string of all lowercase alphabets.

At this point, rather than trying to read documentation or reverse the code, I intuitively guessed the solution. Certain characters are not allowed as inputs, so they are removed from the string, and everything else is simply shuffled in a specific order.

Comparing the sorted input to the sorted output allows us to quickly deduce the unallowed characters, from which we can add uppercase alphabets to our input string until it reaches length 32 (which is the length of the output the challenge provides us with).

Once we are able to craft a successful input consisting of 32 unique allowed characters, we can get the corresponding output on the website. Then, we can write a basic script to figure out the index mapping, and finally reverse the process on the provided output.

# messy code sorry
def find_input_from_output(output_string, input_string, decode_string):
    output_to_input = [-1] * 32
    
    for i in range(len(input_string)):
        for j in range(len(output_string)):
            if output_string[j] == input_string[i] and output_to_input[j] == -1:
                output_to_input[j] = i
                break
    
    input_from_output = ""
    for i in range(len(decode_string)):
        input_from_output += decode_string[output_to_input.index(i)]
    
    return ''.join(input_from_output)

output_example = "jelmnopCrsFtcufwEBy0a1234hADbdgi"
input_example = "ABCDEFabcdefghijlmnoprstuwy01234"
new_output = "1o1i_awlaw_aowsay3wa0awa!iJlooHi"

result = find_input_from_output(output_example, input_example, new_output)
print("vsctf{"+result+"}")

Flag: vsctf{J3lly_0oooosHii11i_awawawawaawa!}