Kleptography

kleptography.py

@@ -0,0 +1,13 @@
+n, m = map(int, input().split())
+knowntext = input()
+ciphertext = input()
+plaintext = [""] * m
+for i in range(n):
+    plaintext[-n + i] = knowntext[i]
+
+for i in range(m - 1, -1, -1):
+    char = chr((ord(ciphertext[i]) - ord(plaintext[i])) % 26 + 97)
+    if i - n >= 0:
+        plaintext[i - n] = char
+
+print("".join(plaintext))