easy peasy

easy_peasy/otp.py

@@ -0,0 +1,51 @@
+#!/usr/bin/python3
+import os.path
+
+KEY_FILE = "key"
+KEY_LEN = 50000
+FLAG_FILE = "flag"
+
+
+def startup(key_location):
+	flag = open(FLAG_FILE).read()
+	kf = open(KEY_FILE, "rb").read()
+
+	start = key_location
+	stop = key_location + len(flag)
+
+	key = kf[start:stop]
+	key_location = stop
+
+	result = list(map(lambda p, k: "{:02x}".format(ord(p) ^ k), flag, key))
+	print("This is the encrypted flag!\n{}\n".format("".join(result)))
+
+	return key_location
+
+def encrypt(key_location):
+	ui = input("What data would you like to encrypt? ").rstrip()
+	if len(ui) == 0 or len(ui) > KEY_LEN:
+		return -1
+
+	start = key_location
+	stop = key_location + len(ui)
+
+	kf = open(KEY_FILE, "rb").read()
+
+	if stop >= KEY_LEN:
+		stop = stop % KEY_LEN
+		key = kf[start:] + kf[:stop]
+	else:
+		key = kf[start:stop]
+	key_location = stop
+
+	result = list(map(lambda p, k: "{:02x}".format(ord(p) ^ k), ui, key))
+
+	print("Here ya go!\n{}\n".format("".join(result)))
+
+	return key_location
+
+
+print("******************Welcome to our OTP implementation!******************")
+c = startup(0)
+while c >= 0:
+	c = encrypt(c)

easy_peasy/sol.py

@@ -0,0 +1,32 @@
+#!/home/maxime/.pyvenv/bin/python3
+from pwn import *
+import binascii
+
+buffersize = 50000-32
+
+conn = remote("mercury.picoctf.net", 36981)
+conn.recvline()
+conn.recvline()
+
+encrypted_flag = conn.recvline().strip()
+
+conn.recvuntil(b'?')
+
+conn.sendline(b'0' * buffersize)
+
+conn.recvuntil(b'?')
+
+conn.sendline(b'0' * 32)
+
+conn.recvline()
+
+encrypted_0s = conn.recvline().strip()
+
+conn.close()
+
+encrypted_flag = binascii.unhexlify(encrypted_flag)
+encrypted_0s = binascii.unhexlify(encrypted_0s)
+for i in range(32):
+    print(chr(encrypted_0s[i] ^ encrypted_flag[i] ^ ord('0')), end='')
+print()
+