Deception

Description

Author: Ryzon

One day, one of Ryzon's imaginary friends, Claudio, mysteriously gives him a text file and says that there is secret information within the file that is impossible to retrieve! So much so that he promises to give Ryzon $1,000,000 if he manages to get the info.

However, Claudio is a humongous troll and tries to deceive Ryzon as much as possible by spamming a bunch of useless information.

Can you help Ryzon retrieve the top-secret information? He promises to share the prize money with you if you do!

rev1.zip

Analysis

zip contains a text file called Answers.txt, each line seems to be Base64 encoded data, using CyberChef we can easily decode the values.

Decoding 4th line of Base64 gives us some Java code.

import java.io.*;
import java.util.*;
import java.time.*;
import java.text.*;
import java.math.*;
public class Deception {
    static FastReader FastReader = new FastReader();
    static BufferedWriter o = new BufferedWriter(new OutputStreamWriter(System.out));
    static PrintWriter pw;

    static char table[] = {
            'd', 'y', 'n', 'm', 'r', '7', '2', '3', '9', '8', 'o', '2', 'm', 'n', 'y', 'l', 'r', 'f', '7', '4', '9',
            '0', '2', '3', 'q', 'y', 'n', 'd', '7', '8', '9', '4', '2', '3', 'y', 'd', '8', '9', 'o', 'q', '7',
            's', 'n', 'g', 'y', 'u', 'i', '2', 'g', 'h', 'u', 'y', 'i', 'c', 'g', 'i', 'k', 'a', 'd', 'l', 'd',
            'g', 'h', 'i', 'w', 'k', 'a', 'l', 'S', 'D', 'H', 'N', 'Q', 'O', '3', '2', '7', 'D', 'Q', '2', 'O',
            '8', 'G', 'D', 'H', '7', '8', 'O', '2', 'Q', 'D', 'N', 'G', 'W', 'U', 'A', 'K', 'D', 'G', 'H', 'X',
            'K', 'J', 'S', 'A', 'G', 'D', '2', 'K', 'S', 'A', 'G', 'I', 'K', 'G', 'I', 'Y', 'K', 'G', 'I', 'K',
            '7', 'i', 'k', 'l', 'f', 'g', '3', 'i', 'k', 'r', 'g', 'f', '3', '8', 'o', '4', '7', 't', 'g', '3',
            '9', '8', 'o', 'f', 'g', 'o', '7', 'i', 'h', 'f', 'k', 'u', 'i', 'a', 'l', 'w', 'e', 'h', 'f', 'i',
            'l', 'w', 'k', 'a', '}', 'h', 'x', 'w', 'l', 'a', 'u', 'k', 'f', 'x', 'n', 'h', 'e', 'a', 'o', 'i',
            'u', 'h', 'x', 'f', 'g', 'a', 'w', 'i', 'o', 'u', 'y', 'g', 'h', 'e', 'a', 'w', '8', 'o', 'n', '7',
            '4', 'w', 'f', '8', 'o', 'n', 'w', 'q', 'g', '7', '8', 'o', '4', 'w', 'a', 'n', 'g', 'h', 'u', 'i',
            'a', 'w', 'e', 'k', '0', 'l', 'f', 'b', 'x', 'c', 'j', 'k', 'a', 's', 'd', 'f', 'b', 'j', 'k', 'a',
            's', 'e', 'f', 'k', 'j', 'a', '7', 'e', 'n', 'f', 'g', 'a', 'i', 'u', 'y', 'w', 'e', 'k', 'f', 'g',
            'y', 'u', 'w', 'e', 'a', 'i', 'o', 'g', 'h', 'x', 'f', 'a', 'e', 'j', 'k', 'w', 'B', 'f', 'w', 'e',
            'a', 'k', 'j', 'f', 'g', 'h', 'a', 'w', '7', 'g', 'v', 'a', 'w', 'u', 'b', 't', '3', '2', 'q', '6',
            '7', '8', 'd', 't', 'b', '3', 'q', '6', '8', 'o', '4', 't', 'q', '7', '8', 'o', 'i', '3', 't', 'r',
            'o', '8', 'c', '7', 'b', 't', '3', '5', 'p', '9', 'q', 't', 'y', '5', 'c', '7', '1', 'b', 'r', 't',
            'c', 'y', '2', '7', '1', '8', 'f', '2', '7', '1', '8', '9', '0', '7', 'n', 'y', '0', '9', '8', 'y',
            'm', 'r', '8', '9', '2', 'm', 'c', '0', '9', '2', 'y', 'i', 'o', 'h', 'u', 'i', 'w', 'h', 'i', 'l',
            'w', 'n', 'h', 'r', 'i', 'u', 'w', 'e', 'k', 'l', 'h', 'n', '8', '2', '7', '0', '3', 'n', 'y', 'r',
            '7', '4', 'j', '3', 'y', 'n', 'r', '7', '8', '3', 'n', 'g', 'h', 'c', 'e', '7', 'u', 'n', 'g', 'c',
            'h', 'o', '3', '7', 'i', '4', 'y', 'h', 'r', 'o', 'i', 'u', 'w', 'e', 'h', 'r', 'i', 'o', 'w', 'n',
            'r', 'u', 'w', 'e', 'i', 'r', 'h', 'n', 'w', 'o', 'u', 'i', 'e', 'n', 'h', 'r', 'i', 'u', 'i', '3',
            'e', 'w', 'n', 'h', 'u', 'i', 'w', 'o', 'h', 'c', 'm', 'r', '7', '8', '4', 'n', 'y', '3', '7', '9',
            '8', '4', '4', '5', '4', '4', '6', 't', '4', '3', '7', '8', '9', '5', '6', '3', '9', '8', '7', 'c',
            'n', 't', '5', 'y', '9', '3', '4', '7', '8', 'n', '5', 't', 'y', 'c', '7', '8', '9', '3', '4', '6',
            'c', '5', '9', '8', '7', '3', '2', '7', '9', 't', 'y', 'b', 'n', '9', 'p', '2', 'y', 'n', 'x', '9',
            '1', '2', 'y', '3', 'r', 'y', 'n', 'd', 'f', '9', '8', 'o', 'r', '7', 'y', 'n', 'm', 'r', 'd', 'o',
            's', '8', '9', '7', 'y', 'n', 'm', 'd', 'r', 'o', 'h', '9', 'q', '7', '0', '4', '2', 'd', 'r', 'y',
            'n', 'm', '9', '3', '2', 'q', '7', '8', '9', 'd', 'y', 'm', '4', 'o', 'q', '8', 't', '9', 'r', 'n',
            'y', 'm', 'f', 'o', 'q', '8', '9', '3', 'f', 'y', 'm', 'n', 'y', '3', 'q', '8', '}', 'o', 'd', 'r',
            'm', 'n', 'y', 'q', '9', '2', '3', '8', '7', 'y', '7', '8', '9', '5', 'y', 'q', '9', 'd', 'o', 'y',
            'l', 'a', 'y', 'a', 'l', 'y', 'd', '9', 'y', 'n', 'l', 'y', 'i', '7', 'N', '7', 'F', 'C', 'N', 'G',
            'H', '3', 'I', 'W', 'Y', 'U', 'T', 'G', 'N', '3', 'I', '7', 'f', '4', 'T', 'G', '8', '7', '3', '6',
            'I', 'W', 'T', '5', 'Y', '7', '8', 'W', '3', '4', 'O', 'N', 'F', 'C', 'B', 'O', 'd', '3', '7', 'N',
            'Y', 'F', 'R', '4', 'N', '7', 'U', 'I', 'Y', 'E', 'K', 'L', 'S', 'H', 'A', 'I', 'U', 'H', 'E', 'R',
            'F', 'U', 'A', 'I', 'W', 'K', 'R', 'N', 'o', 'F', 'H', 'A', 'O', '7', '8', '4', 'Y', '7', 'O', '8',
            'Y', '7', '8', 'O', 'Y', 'N', '7', '8', '4', 'Y', 'N', 'R', 'Q', '7', 'O', '8', '1', '4', '9', 'R',
            'Y', 'N', 'M', 'C', 'Q', '3', 'd', 'R', 'C', 'N', 'Y', '7', 'Q', 'O', 'I', '3', 'U', 'N', 'Y', 'C',
            'H', 'R', 'I', 'L', 'U', 'H', 'I', 'L', 'W', 'A', 'H', 'E', 'R', 'U', '1', 'W', 'L', 'N', 'H', 'C',
            'U', 'I', 'W', '4', 'A', 'N', 'Y', 'H', 'R', 'C', '4', 'A', 'O', '8', '7', '9', 'R', 'Y', 'N', '7',
            'C', 'A', '8', 'Y', 'R', 'C', 'N', '7', '8', 'O', 'A', 'R', 'Y', 'C', 'o', '7', '8', '8', 'O', 'C',
            'R', 'Y', 'N', 'M', 'A', 'C', '7', 'N', 'R', 'H', 'A', 'E', 'I', 'U', 'w', 'O', 'H', 'N', 'R', 'C',
            'A', 'W', 'U', 'I', 'O', 'N', 'H', 'O', 'U', 'I', '3', '7', '8', '6', '2', '8', 'j', '2', '6', '7',
            '8', '9', '1', '6', '4', '7', '8', '9', 'n', '6', 'd', 'x', '9', '8', '7', '2', '3', 'n', 'y', '4',
            '7', '8', '2', 'y', 'x', 'e', '9', 'd', 'h', '2', '7', '3', '8', 'h', 'n', 'x', '7', '8', '9', '2',
            '1', '5', '4', '4', '6', 't', '4', '3', '7', '8', '9', '5', '1', '3', '9', '8', '7', 'p', 'P', 'c',
            'n', 't', '5', 'y', '9', '3', '4', '7', 'd', 'n', '5', 't', 'y', 'c', '7', '8', '9', '3', '4', '6',
            'c', '5', '9', '8', '7', '3', '2', '7', '9', 't', 'y', 'b', 'n', '9', 'p', '2', 'y', 'n', 'x', '9',
            'o', '2', 'y', '3', 'r', 'y', 'n', 'd', 'f', '9', '8', 'o', 'r', '7', 'y', 'n', 'm', 'r', 'd', 'o',
            'q', '8', '9', '7', 'y', 'n', 'm', 'd', 'r', 'o', '8', '9', 'q', '7', '3', '4', '2', 'd', 'r', 'y',
            'n', 'm', 'o', '3', '2', 'q', '7', '8', '9', 'd', 'y', 'm', '4', 'o', 'q', '8', 'p', '9', 'r', 'n',
            'y', 'm', 'f', 'o', 'j', '8', '9', '3', 'f', 'y', 'm', 'n', '7', '3', 'q', '8', '9', 'o', 'd', 'r',
            'm', 'n', 'y', 'q', 'j', '2', '3', '8', '7', 'y', '7', '8', 'l', '5', 'y', 'q', '9', 'd', 'o', 'y',
            'l', 'a', 'y', 'a', 'l', 'y', 'd', '9', '9', 'n', 'l', 'y', 'i', '7', 'N', '7', 'F', 'C', 'N', 'G',
            'H', '3', 'I', 'W', 'Y'
    };

    public static void main(String[] args) throws Exception {
        System.out.println("Welcome to the LMD Machine 3000!");
        System.out.println("Please enter an integer: ");

        int input = readInt();

        System.out.println();

        if (input < 1 || input > table.length) {
            System.out.println("Invalid Input");
            System.exit(0);
        }

        System.out.print("ctf{");

        for (int i = 0, idx = 1; i < 15; ++i) {
            idx = (idx * input) % table.length;
            System.out.print(table[idx]);
        }

        System.out.println("}");
    }

    static int readInt() {return FastReader.readInt();}
    static long readLong() {return FastReader.readLong();}
    static double readDouble() {return FastReader.readDouble();}
    static float readFloat() {return FastReader.readFloat();}
    static String readLine() {return FastReader.readLine();}
    static String next() {return FastReader.next();}
    static boolean readBool() {return FastReader.readBool();}

    static class FastReader extends PrintWriter {
        private final InputStream stream;
        private final byte[] buf = new byte[1 << 16];
        private int curChar, numChars;
        public FastReader() {this(System.in, System.out);}
        public FastReader(InputStream i, OutputStream o) {super(o);stream = i;}
        public FastReader(String i, String o) throws IOException {
            super(new FileWriter(o)); stream = new FileInputStream(i);
        }
        private int readByte() {
            if (numChars == -1) {throw new InputMismatchException();}
            if (curChar >= numChars) {
                curChar = 0;
                try {numChars = stream.read(buf);
                }catch(Exception e){throw new InputMismatchException();}
                if (numChars == -1) {return -1;}
            }
            return buf[curChar++];
        }
        public String next() {
            int c; do {c = readByte();} while (c <= ' ');
            StringBuilder res = new StringBuilder();
            do {res.appendCodePoint(c);c = readByte();} while (c > ' ');
            return res.toString();
        }
        public String readLine() {
            int c; do {c = readByte();} while (isEndLine(c));
            StringBuilder res = new StringBuilder();
            do {res.appendCodePoint(c);c = readByte();} while (c >= ' ');
            return res.toString();
        }
        public int readInt() {
            int c, sgn = 1, res = 0;
            do {c = readByte();} while (c <= ' ');
            if (c == '-') {sgn = -1;c = readByte();}
            do {
                if (c < '0' || c > '9') {throw new InputMismatchException();}
                res = 10 * res + c - '0';c = readByte();
            } while (c > ' ');
            return res * sgn;
        }

        /**
         * Psst
         *
         * https://drive.google.com/file/d/1oDDXyVxYHqdGB6H2bddUxbRL3z39SZb3/view?usp=sharing
         */

        public double readDouble() {return Double.parseDouble(next());}
        public long readLong() {return Long.parseLong(next());}
        public float readFloat() {return Float.parseFloat(next());}
        public boolean readBool() {return Boolean.parseBoolean(next());}
        boolean isEndLine(int c) {return c == '\n' || c == '\r' || c == -1;}
    }
}

The Java code seems to take number as input (from 0 to len(table)) and do an encryption of some kind.

But first we have a hint.

Open Google Drive Link -> Copy Key -> Decode Brainf*ck -> Decode Base64 ->

Roses are red, Violets are blue, If one wants to pick the correct flag, Then they should seek the Unix Epoch as a clue

Hmm... wants to pick the correct flag, we probably can't get flag directly from the hint. If we generate all possible keys that Program can generate and sift it we'll probably be able to pick the correct flag.

└─$ javac Deception.java
Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=on -Dswing.aatext=true
                                                     
└─$ ls
 Deception$FastReader.class   Deception.class   Deception.java

# Generate flags from 1 to len(table)
└─$ for i in {1..1106}; do (echo -n $i | java Deception | grep "ctf") >> guessing.log; done;

# Get the flag              # Epoch start (year)    
└─$ cat guessing.log | grep 1970   
ctf{REDACTED}