Create README.md

squ1rrel-ctf-2024/bf-golfing/README.md

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+# bf golfing
+
+i am mad fr that the challenge changed from 90 to 100 char instead of 90 to 91 char. mad mad mad asf
+
+## problem
+
+![image](https://github.com/quasar098/ctf-writeups/assets/70716985/fdf2ecb5-d1b4-468f-a785-3b82ae7c312b)
+
+```py
+def run_brainfuck(code):
+    if len(code) > 90:
+        return "Error: Code length exceeds 90 characters."
+
+    tape = [0] * 30000
+    ptr = 0
+    code_ptr = 0
+    output = []
+    brackets = []
+    max_steps = 200000
+    step_count = 0
+
+    while code_ptr < len(code) and step_count < max_steps:
+        command = code[code_ptr]
+        if command == '>':
+            ptr += 1
+        elif command == '<':
+            ptr -= 1
+        elif command == '+':
+            tape[ptr] = (tape[ptr] + 1) % 256
+        elif command == '-':
+            tape[ptr] = (tape[ptr] - 1) % 256
+        elif command == '.':
+            output.append(chr(tape[ptr]))
+        elif command == '[':
+            if tape[ptr] == 0:
+                depth = 1
+                while depth and code_ptr < len(code):
+                    code_ptr += 1
+                    if code[code_ptr] == '[':
+                        depth += 1
+                    elif code[code_ptr] == ']':
+                        depth -= 1
+            else:
+                brackets.append(code_ptr)
+        elif command == ']':
+            if tape[ptr] != 0:
+                code_ptr = brackets[-1]
+            else:
+                brackets.pop()
+        code_ptr += 1
+        step_count += 1
+
+    if step_count >= max_steps:
+        return None  # Indicate that the program was terminated due to too many steps
+
+    return ''.join(output)
+
+
+print("how well can you read and write code now?")
+bf_code = input()
+expected_output = 'squ1rrel{es0g01f}'
+actual_output = run_brainfuck(bf_code)
+
+if expected_output != actual_output:
+    print("does your brain hurt yet?")
+    exit(1)
+else:
+    print("squ1rrel{test_flag}")
+```
+
+## solution
+
+the goal is to make a program that outputs `squ1rrel{es0g01f}` and then we get the real flag
+
+i tried making one manually, but it was too big (117 chars)
+
+`+++[[<+>>++<-]>]<<<<+++[-<<+<+<+<+>>>>>]<<<++++.--.++++.>>+.<<---..<<-.>+++.>>.<<<.>>+.>>-.<<<<++.>>>>.+.<<<<-.>>>++.` my manual solution
+
+from [https://codegolf.stackexchange.com/questions/55422/hello-world](https://codegolf.stackexchange.com/questions/55422/hello-world)
+
+![image](https://github.com/quasar098/ctf-writeups/assets/70716985/cf5f8614-47ec-465a-9255-4ef560da5973)
+
+this 72 byte solution was found using brute force
+
+![image](https://github.com/quasar098/ctf-writeups/assets/70716985/7e6ae9d4-f838-45d2-baa4-1eb15d634b7c)
+
+see the repo [here](https://github.com/ksabry/bfbrute/tree/master)
+
+![image](https://github.com/quasar098/ctf-writeups/assets/70716985/620e9e7e-fd58-49b5-a8c6-c418c0c434ad)
+
+![image](https://github.com/quasar098/ctf-writeups/assets/70716985/c87cd4bf-e82b-45e7-a3de-db87db0719c6)
+
+i changed the output to the goal output, and also changed the below
+
+![image](https://github.com/quasar098/ctf-writeups/assets/70716985/77a2c834-e23d-4e95-a57d-961fa8a3e5a4)
+
+i set the threads to be 12 (the amount that my cpu has), and the SIZE_START to 24 (this seemed to be the ideal number).
+
+i noticed the program runs a lot faster if the SHOW_ALL_PROGRAMS_LENGTH is lower, so i set it to 100.
+
+i generated a lot of below 100 ones, but the best one i generated was `+[[+<->>>]<--<-<<<+<-<-]<<<------.--.++++.<-.>---..<<<-.<.<-.>>.>>>+.<-.<<++.>>.+.<<-.<<++.`, which is 91 bytes.
+
+unfortunately, they raised the limit to 100 which is wayyyy too easy.
+
+```terminal
+quasar@quasar098:~/Downloads$ nc 34.132.166.199 11111
+how well can you read and write code now?
++[[+<->>>]<--<-<<<+<-<-]<<<------.--.++++.<-.>---..<<<-.<.<-.>>.>>>+.<-.<<++.>>.+.<<-.<<++.
+squ1rrel{g3n1u5_0r_brut3f0rc3d??!?}
+```