Day 20 solved

Day 20/decode.py

@@ -0,0 +1,19 @@
+
+byte_300 = [0xCE, 0x55, 0x95, 0x4E, 0x38, 0x0C5, 0x89, 0x0A5, 0x1B, 0x6F, 0x5E, 0x25, 0x0D2, 0x1D, 0x2A, 0x2B, 0x5E, 0x7B, 0x39, 0x14, 0x8E, 0x0D0, 0x0F0, 0x0F8, 0x0F8, 0x0A5, 0x00]
+
+with open("PS4UPDATE.PUP", "rb") as f:
+
+    v29 = byte_300.copy()
+    v14 = 4919;
+
+    while True:
+        f.seek(v14)
+        input = bytes(f.read(27))
+        for i in range(27):
+            v29[i] = (v29[i] ^ input[i])
+
+        v14 += 4919
+        if v14 == 24201480: # 4920 times
+            break
+
+    print("".join(chr(x) for x in v29))