Day 15 + Day 17

Day 17/decrypt.sage

@@ -0,0 +1,46 @@
+from Crypto.Util.number import long_to_bytes, bytes_to_long
+from PIL import Image
+from hackingscripts import util
+
+def extract_bin(pixels):
+    bin_stream = ""
+    for p in pixels:
+        r = util.lpad(bin(p[0])[2:], n, "0")
+        g = util.lpad(bin(p[1])[2:], n, "0")
+        b = util.lpad(bin(p[2])[2:], n, "0")
+        bin_stream += r + g + b
+    return bin_stream
+
+if __name__ == "__main__":
+    key_img = Image.open("key.png")
+    pix = key_img.load()
+    width, height = key_img.size
+
+    pixels_p = []
+    pixels_q = []
+    end_p = (54, 20)
+    end_q = (54, 41)
+
+    for y in range(height):
+        for x in range(width):
+            if y <= end_p[1]:
+                pixels_p.append(pix[x,y])
+            else:
+                pixels_q.append(pix[x,y])
+
+    p = int(extract_bin(pixels_p), 2)
+    q = int(extract_bin(pixels_q), 2)
+
+    e = 0x10001
+    n = p * q
+    phi_n = (p - 1) * (q - 1)
+    d = power_mod(e, -1, phi_n)
+
+    with open("flag.enc", "rb") as f:
+        data = f.read()
+        ct = bytes_to_long(data)
+        pt = power_mod(ct, d, n)
+        pt_b = long_to_bytes(pt) 
+        with open("decrypted.png", "wb") as g:
+            g.write(pt_b)
+