166

README.md

@@ -8,3 +8,11 @@ The folder name is the challenge id, as found in the URL (<https://play.picoctf.
 Inside the folder there is an `inputs` subfolder which just includes all the files from the challenge description.
 
 Executing `nix run .#CHALLENGE_ID` runs the challenge.
+
+## 156 - "Nice netcat..."
+
+```txt
+nc mercury.picoctf.net 49039
+```
+
+Output is in ASCII. Convert to text.

exercises/166/inputs/flag.txt.en

@@ -0,0 +1 @@
+gAAAAABgUAIV8D5MJdzgLLTkkMlbU84ARVwfX4brMt2rJQCjkpLItytfWVZe1L2dp4K8VrKgRU3axStKJEAqcM0iDaxiYE54Boh8UfAAo1RNifKnlDrFz0gLaznVSFVj2xAUa4V35180

exercises/166/inputs/pw.txt

@@ -0,0 +1 @@
+68f88f9368f88f9368f88f9368f88f93

exercises/166/main.py

@@ -0,0 +1,60 @@
+
+import sys
+import base64
+from cryptography.fernet import Fernet
+
+
+
+usage_msg = "Usage: "+ sys.argv[0] +" (-e/-d) [file]"
+help_msg = usage_msg + "\n" +\
+        "Examples:\n" +\
+        "  To decrypt a file named 'pole.txt', do: " +\
+        "'$ python "+ sys.argv[0] +" -d pole.txt'\n"
+
+
+
+if len(sys.argv) < 2 or len(sys.argv) > 4:
+    print(usage_msg)
+    sys.exit(1)
+
+
+
+if sys.argv[1] == "-e":
+    if len(sys.argv) < 4:
+        sim_sala_bim = input("Please enter the password:")
+    else:
+        sim_sala_bim = sys.argv[3]
+
+    ssb_b64 = base64.b64encode(sim_sala_bim.encode())
+    c = Fernet(ssb_b64)
+
+    with open(sys.argv[2], "rb") as f:
+        data = f.read()
+        data_c = c.encrypt(data)
+        sys.stdout.write(data_c.decode())
+
+
+elif sys.argv[1] == "-d":
+    if len(sys.argv) < 4:
+        sim_sala_bim = input("Please enter the password:")
+    else:
+        sim_sala_bim = sys.argv[3]
+
+    ssb_b64 = base64.b64encode(sim_sala_bim.encode())
+    c = Fernet(ssb_b64)
+
+    with open(sys.argv[2], "r") as f:
+        data = f.read()
+        data_c = c.decrypt(data.encode())
+        sys.stdout.buffer.write(data_c)
+
+
+elif sys.argv[1] == "-h" or sys.argv[1] == "--help":
+    print(help_msg)
+    sys.exit(1)
+
+
+else:
+    print("Unrecognized first argument: "+ sys.argv[1])
+    print("Please use '-e', '-d', or '-h'.")
+

flake.nix

@@ -20,7 +20,7 @@
     packages.${system} = forAllExercises (
       exercise:
         pkgs.writers.writePython3Bin "picoCTF_${exercise}" {
-          #libraries = with pkgs.python3.pkgs; [requests];
+          libraries = with pkgs.python3.pkgs; [cryptography];
         } "${builtins.readFile ./exercises/${exercise}/main.py}"
     );